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/*
* Copyright (c) 2010-2017 ARM Limited
* All rights reserved.
*
* The license below extends only to copyright in the software and shall
* not be construed as granting a license to any other intellectual
* property including but not limited to intellectual property relating
* to a hardware implementation of the functionality of the software
* licensed hereunder. You may use the software subject to the license
* terms below provided that you ensure that this notice is replicated
* unmodified and in its entirety in all distributions of the software,
* modified or unmodified, in source code or in binary form.
*
* Copyright (c) 2002-2005 The Regents of The University of Michigan
* Copyright (c) 2010,2015 Advanced Micro Devices, Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Erik Hallnor
* Dave Greene
* Nathan Binkert
* Steve Reinhardt
* Ron Dreslinski
* Andreas Sandberg
* Nikos Nikoleris
*/
/**
* @file
* Cache definitions.
*/
#include "mem/cache/cache.hh"
#include "base/logging.hh"
#include "base/types.hh"
#include "debug/Cache.hh"
#include "debug/CachePort.hh"
#include "debug/CacheTags.hh"
#include "debug/CacheVerbose.hh"
#include "mem/cache/blk.hh"
#include "mem/cache/mshr.hh"
#include "mem/cache/prefetch/base.hh"
#include "sim/sim_exit.hh"
Cache::Cache(const CacheParams *p)
: BaseCache(p, p->system->cacheLineSize()),
tags(p->tags),
prefetcher(p->prefetcher),
doFastWrites(true),
prefetchOnAccess(p->prefetch_on_access),
clusivity(p->clusivity),
writebackClean(p->writeback_clean),
tempBlockWriteback(nullptr),
writebackTempBlockAtomicEvent([this]{ writebackTempBlockAtomic(); },
name(), false,
EventBase::Delayed_Writeback_Pri)
{
tempBlock = new CacheBlk();
tempBlock->data = new uint8_t[blkSize];
cpuSidePort = new CpuSidePort(p->name + ".cpu_side", this,
"CpuSidePort");
memSidePort = new MemSidePort(p->name + ".mem_side", this,
"MemSidePort");
tags->setCache(this);
if (prefetcher)
prefetcher->setCache(this);
}
Cache::~Cache()
{
delete [] tempBlock->data;
delete tempBlock;
delete cpuSidePort;
delete memSidePort;
}
void
Cache::regStats()
{
BaseCache::regStats();
}
void
Cache::cmpAndSwap(CacheBlk *blk, PacketPtr pkt)
{
assert(pkt->isRequest());
uint64_t overwrite_val;
bool overwrite_mem;
uint64_t condition_val64;
uint32_t condition_val32;
int offset = tags->extractBlkOffset(pkt->getAddr());
uint8_t *blk_data = blk->data + offset;
assert(sizeof(uint64_t) >= pkt->getSize());
overwrite_mem = true;
// keep a copy of our possible write value, and copy what is at the
// memory address into the packet
pkt->writeData((uint8_t *)&overwrite_val);
pkt->setData(blk_data);
if (pkt->req->isCondSwap()) {
if (pkt->getSize() == sizeof(uint64_t)) {
condition_val64 = pkt->req->getExtraData();
overwrite_mem = !std::memcmp(&condition_val64, blk_data,
sizeof(uint64_t));
} else if (pkt->getSize() == sizeof(uint32_t)) {
condition_val32 = (uint32_t)pkt->req->getExtraData();
overwrite_mem = !std::memcmp(&condition_val32, blk_data,
sizeof(uint32_t));
} else
panic("Invalid size for conditional read/write\n");
}
if (overwrite_mem) {
std::memcpy(blk_data, &overwrite_val, pkt->getSize());
blk->status |= BlkDirty;
}
}
void
Cache::satisfyRequest(PacketPtr pkt, CacheBlk *blk,
bool deferred_response, bool pending_downgrade)
{
assert(pkt->isRequest());
assert(blk && blk->isValid());
// Occasionally this is not true... if we are a lower-level cache
// satisfying a string of Read and ReadEx requests from
// upper-level caches, a Read will mark the block as shared but we
// can satisfy a following ReadEx anyway since we can rely on the
// Read requester(s) to have buffered the ReadEx snoop and to
// invalidate their blocks after receiving them.
// assert(!pkt->needsWritable() || blk->isWritable());
assert(pkt->getOffset(blkSize) + pkt->getSize() <= blkSize);
// Check RMW operations first since both isRead() and
// isWrite() will be true for them
if (pkt->cmd == MemCmd::SwapReq) {
cmpAndSwap(blk, pkt);
} else if (pkt->isWrite()) {
// we have the block in a writable state and can go ahead,
// note that the line may be also be considered writable in
// downstream caches along the path to memory, but always
// Exclusive, and never Modified
assert(blk->isWritable());
// Write or WriteLine at the first cache with block in writable state
if (blk->checkWrite(pkt)) {
pkt->writeDataToBlock(blk->data, blkSize);
}
// Always mark the line as dirty (and thus transition to the
// Modified state) even if we are a failed StoreCond so we
// supply data to any snoops that have appended themselves to
// this cache before knowing the store will fail.
blk->status |= BlkDirty;
DPRINTF(CacheVerbose, "%s for %s (write)\n", __func__, pkt->print());
} else if (pkt->isRead()) {
if (pkt->isLLSC()) {
blk->trackLoadLocked(pkt);
}
// all read responses have a data payload
assert(pkt->hasRespData());
pkt->setDataFromBlock(blk->data, blkSize);
// determine if this read is from a (coherent) cache or not
if (pkt->fromCache()) {
assert(pkt->getSize() == blkSize);
// special handling for coherent block requests from
// upper-level caches
if (pkt->needsWritable()) {
// sanity check
assert(pkt->cmd == MemCmd::ReadExReq ||
pkt->cmd == MemCmd::SCUpgradeFailReq);
assert(!pkt->hasSharers());
// if we have a dirty copy, make sure the recipient
// keeps it marked dirty (in the modified state)
if (blk->isDirty()) {
pkt->setCacheResponding();
blk->status &= ~BlkDirty;
}
} else if (blk->isWritable() && !pending_downgrade &&
!pkt->hasSharers() &&
pkt->cmd != MemCmd::ReadCleanReq) {
// we can give the requester a writable copy on a read
// request if:
// - we have a writable copy at this level (& below)
// - we don't have a pending snoop from below
// signaling another read request
// - no other cache above has a copy (otherwise it
// would have set hasSharers flag when
// snooping the packet)
// - the read has explicitly asked for a clean
// copy of the line
if (blk->isDirty()) {
// special considerations if we're owner:
if (!deferred_response) {
// respond with the line in Modified state
// (cacheResponding set, hasSharers not set)
pkt->setCacheResponding();
// if this cache is mostly inclusive, we
// keep the block in the Exclusive state,
// and pass it upwards as Modified
// (writable and dirty), hence we have
// multiple caches, all on the same path
// towards memory, all considering the
// same block writable, but only one
// considering it Modified
// we get away with multiple caches (on
// the same path to memory) considering
// the block writeable as we always enter
// the cache hierarchy through a cache,
// and first snoop upwards in all other
// branches
blk->status &= ~BlkDirty;
} else {
// if we're responding after our own miss,
// there's a window where the recipient didn't
// know it was getting ownership and may not
// have responded to snoops correctly, so we
// have to respond with a shared line
pkt->setHasSharers();
}
}
} else {
// otherwise only respond with a shared copy
pkt->setHasSharers();
}
}
} else if (pkt->isUpgrade()) {
// sanity check
assert(!pkt->hasSharers());
if (blk->isDirty()) {
// we were in the Owned state, and a cache above us that
// has the line in Shared state needs to be made aware
// that the data it already has is in fact dirty
pkt->setCacheResponding();
blk->status &= ~BlkDirty;
}
} else {
assert(pkt->isInvalidate());
invalidateBlock(blk);
DPRINTF(CacheVerbose, "%s for %s (invalidation)\n", __func__,
pkt->print());
}
}
/////////////////////////////////////////////////////
//
// Access path: requests coming in from the CPU side
//
/////////////////////////////////////////////////////
bool
Cache::access(PacketPtr pkt, CacheBlk *&blk, Cycles &lat,
PacketList &writebacks)
{
// sanity check
assert(pkt->isRequest());
chatty_assert(!(isReadOnly && pkt->isWrite()),
"Should never see a write in a read-only cache %s\n",
name());
DPRINTF(CacheVerbose, "%s for %s\n", __func__, pkt->print());
if (pkt->req->isUncacheable()) {
DPRINTF(Cache, "uncacheable: %s\n", pkt->print());
// flush and invalidate any existing block
CacheBlk *old_blk(tags->findBlock(pkt->getAddr(), pkt->isSecure()));
if (old_blk && old_blk->isValid()) {
if (old_blk->isDirty() || writebackClean)
writebacks.push_back(writebackBlk(old_blk));
else
writebacks.push_back(cleanEvictBlk(old_blk));
invalidateBlock(old_blk);
}
blk = nullptr;
// lookupLatency is the latency in case the request is uncacheable.
lat = lookupLatency;
return false;
}
// Here lat is the value passed as parameter to accessBlock() function
// that can modify its value.
blk = tags->accessBlock(pkt->getAddr(), pkt->isSecure(), lat);
DPRINTF(Cache, "%s %s\n", pkt->print(),
blk ? "hit " + blk->print() : "miss");
if (pkt->req->isCacheMaintenance()) {
// A cache maintenance operation is always forwarded to the
// memory below even if the block is found in dirty state.
// We defer any changes to the state of the block until we
// create and mark as in service the mshr for the downstream
// packet.
return false;
}
if (pkt->isEviction()) {
// We check for presence of block in above caches before issuing
// Writeback or CleanEvict to write buffer. Therefore the only
// possible cases can be of a CleanEvict packet coming from above
// encountering a Writeback generated in this cache peer cache and
// waiting in the write buffer. Cases of upper level peer caches
// generating CleanEvict and Writeback or simply CleanEvict and
// CleanEvict almost simultaneously will be caught by snoops sent out
// by crossbar.
WriteQueueEntry *wb_entry = writeBuffer.findMatch(pkt->getAddr(),
pkt->isSecure());
if (wb_entry) {
assert(wb_entry->getNumTargets() == 1);
PacketPtr wbPkt = wb_entry->getTarget()->pkt;
assert(wbPkt->isWriteback());
if (pkt->isCleanEviction()) {
// The CleanEvict and WritebackClean snoops into other
// peer caches of the same level while traversing the
// crossbar. If a copy of the block is found, the
// packet is deleted in the crossbar. Hence, none of
// the other upper level caches connected to this
// cache have the block, so we can clear the
// BLOCK_CACHED flag in the Writeback if set and
// discard the CleanEvict by returning true.
wbPkt->clearBlockCached();
return true;
} else {
assert(pkt->cmd == MemCmd::WritebackDirty);
// Dirty writeback from above trumps our clean
// writeback... discard here
// Note: markInService will remove entry from writeback buffer.
markInService(wb_entry);
delete wbPkt;
}
}
}
// Writeback handling is special case. We can write the block into
// the cache without having a writeable copy (or any copy at all).
if (pkt->isWriteback()) {
assert(blkSize == pkt->getSize());
// we could get a clean writeback while we are having
// outstanding accesses to a block, do the simple thing for
// now and drop the clean writeback so that we do not upset
// any ordering/decisions about ownership already taken
if (pkt->cmd == MemCmd::WritebackClean &&
mshrQueue.findMatch(pkt->getAddr(), pkt->isSecure())) {
DPRINTF(Cache, "Clean writeback %#llx to block with MSHR, "
"dropping\n", pkt->getAddr());
return true;
}
if (blk == nullptr) {
// need to do a replacement
blk = allocateBlock(pkt->getAddr(), pkt->isSecure(), writebacks);
if (blk == nullptr) {
// no replaceable block available: give up, fwd to next level.
incMissCount(pkt);
return false;
}
tags->insertBlock(pkt, blk);
blk->status = (BlkValid | BlkReadable);
if (pkt->isSecure()) {
blk->status |= BlkSecure;
}
}
// only mark the block dirty if we got a writeback command,
// and leave it as is for a clean writeback
if (pkt->cmd == MemCmd::WritebackDirty) {
blk->status |= BlkDirty;
}
// if the packet does not have sharers, it is passing
// writable, and we got the writeback in Modified or Exclusive
// state, if not we are in the Owned or Shared state
if (!pkt->hasSharers()) {
blk->status |= BlkWritable;
}
// nothing else to do; writeback doesn't expect response
assert(!pkt->needsResponse());
std::memcpy(blk->data, pkt->getConstPtr<uint8_t>(), blkSize);
DPRINTF(Cache, "%s new state is %s\n", __func__, blk->print());
incHitCount(pkt);
return true;
} else if (pkt->cmd == MemCmd::CleanEvict) {
if (blk != nullptr) {
// Found the block in the tags, need to stop CleanEvict from
// propagating further down the hierarchy. Returning true will
// treat the CleanEvict like a satisfied write request and delete
// it.
return true;
}
// We didn't find the block here, propagate the CleanEvict further
// down the memory hierarchy. Returning false will treat the CleanEvict
// like a Writeback which could not find a replaceable block so has to
// go to next level.
return false;
} else if (pkt->cmd == MemCmd::WriteClean) {
// WriteClean handling is a special case. We can allocate a
// block directly if it doesn't exist and we can update the
// block immediately. The WriteClean transfers the ownership
// of the block as well.
assert(blkSize == pkt->getSize());
if (!blk) {
if (pkt->writeThrough()) {
// if this is a write through packet, we don't try to
// allocate if the block is not present
return false;
} else {
// a writeback that misses needs to allocate a new block
blk = allocateBlock(pkt->getAddr(), pkt->isSecure(),
writebacks);
if (!blk) {
// no replaceable block available: give up, fwd to
// next level.
incMissCount(pkt);
return false;
}
tags->insertBlock(pkt, blk);
blk->status = (BlkValid | BlkReadable);
if (pkt->isSecure()) {
blk->status |= BlkSecure;
}
}
}
// at this point either this is a writeback or a write-through
// write clean operation and the block is already in this
// cache, we need to update the data and the block flags
assert(blk);
if (!pkt->writeThrough()) {
blk->status |= BlkDirty;
}
// nothing else to do; writeback doesn't expect response
assert(!pkt->needsResponse());
std::memcpy(blk->data, pkt->getConstPtr<uint8_t>(), blkSize);
DPRINTF(Cache, "%s new state is %s\n", __func__, blk->print());
incHitCount(pkt);
// populate the time when the block will be ready to access.
blk->whenReady = clockEdge(fillLatency) + pkt->headerDelay +
pkt->payloadDelay;
// if this a write-through packet it will be sent to cache
// below
return !pkt->writeThrough();
} else if (blk && (pkt->needsWritable() ? blk->isWritable() :
blk->isReadable())) {
// OK to satisfy access
incHitCount(pkt);
satisfyRequest(pkt, blk);
maintainClusivity(pkt->fromCache(), blk);
return true;
}
// Can't satisfy access normally... either no block (blk == nullptr)
// or have block but need writable
incMissCount(pkt);
if (blk == nullptr && pkt->isLLSC() && pkt->isWrite()) {
// complete miss on store conditional... just give up now
pkt->req->setExtraData(0);
return true;
}
return false;
}
void
Cache::maintainClusivity(bool from_cache, CacheBlk *blk)
{
if (from_cache && blk && blk->isValid() && !blk->isDirty() &&
clusivity == Enums::mostly_excl) {
// if we have responded to a cache, and our block is still
// valid, but not dirty, and this cache is mostly exclusive
// with respect to the cache above, drop the block
invalidateBlock(blk);
}
}
void
Cache::doWritebacks(PacketList& writebacks, Tick forward_time)
{
while (!writebacks.empty()) {
PacketPtr wbPkt = writebacks.front();
// We use forwardLatency here because we are copying writebacks to
// write buffer.
// Call isCachedAbove for Writebacks, CleanEvicts and
// WriteCleans to discover if the block is cached above.
if (isCachedAbove(wbPkt)) {
if (wbPkt->cmd == MemCmd::CleanEvict) {
// Delete CleanEvict because cached copies exist above. The
// packet destructor will delete the request object because
// this is a non-snoop request packet which does not require a
// response.
delete wbPkt;
} else if (wbPkt->cmd == MemCmd::WritebackClean) {
// clean writeback, do not send since the block is
// still cached above
assert(writebackClean);
delete wbPkt;
} else {
assert(wbPkt->cmd == MemCmd::WritebackDirty ||
wbPkt->cmd == MemCmd::WriteClean);
// Set BLOCK_CACHED flag in Writeback and send below, so that
// the Writeback does not reset the bit corresponding to this
// address in the snoop filter below.
wbPkt->setBlockCached();
allocateWriteBuffer(wbPkt, forward_time);
}
} else {
// If the block is not cached above, send packet below. Both
// CleanEvict and Writeback with BLOCK_CACHED flag cleared will
// reset the bit corresponding to this address in the snoop filter
// below.
allocateWriteBuffer(wbPkt, forward_time);
}
writebacks.pop_front();
}
}
void
Cache::doWritebacksAtomic(PacketList& writebacks)
{
while (!writebacks.empty()) {
PacketPtr wbPkt = writebacks.front();
// Call isCachedAbove for both Writebacks and CleanEvicts. If
// isCachedAbove returns true we set BLOCK_CACHED flag in Writebacks
// and discard CleanEvicts.
if (isCachedAbove(wbPkt, false)) {
if (wbPkt->cmd == MemCmd::WritebackDirty ||
wbPkt->cmd == MemCmd::WriteClean) {
// Set BLOCK_CACHED flag in Writeback and send below,
// so that the Writeback does not reset the bit
// corresponding to this address in the snoop filter
// below. We can discard CleanEvicts because cached
// copies exist above. Atomic mode isCachedAbove
// modifies packet to set BLOCK_CACHED flag
memSidePort->sendAtomic(wbPkt);
}
} else {
// If the block is not cached above, send packet below. Both
// CleanEvict and Writeback with BLOCK_CACHED flag cleared will
// reset the bit corresponding to this address in the snoop filter
// below.
memSidePort->sendAtomic(wbPkt);
}
writebacks.pop_front();
// In case of CleanEvicts, the packet destructor will delete the
// request object because this is a non-snoop request packet which
// does not require a response.
delete wbPkt;
}
}
void
Cache::recvTimingSnoopResp(PacketPtr pkt)
{
DPRINTF(Cache, "%s for %s\n", __func__, pkt->print());
assert(pkt->isResponse());
assert(!system->bypassCaches());
// determine if the response is from a snoop request we created
// (in which case it should be in the outstandingSnoop), or if we
// merely forwarded someone else's snoop request
const bool forwardAsSnoop = outstandingSnoop.find(pkt->req) ==
outstandingSnoop.end();
if (!forwardAsSnoop) {
// the packet came from this cache, so sink it here and do not
// forward it
assert(pkt->cmd == MemCmd::HardPFResp);
outstandingSnoop.erase(pkt->req);
DPRINTF(Cache, "Got prefetch response from above for addr "
"%#llx (%s)\n", pkt->getAddr(), pkt->isSecure() ? "s" : "ns");
recvTimingResp(pkt);
return;
}
// forwardLatency is set here because there is a response from an
// upper level cache.
// To pay the delay that occurs if the packet comes from the bus,
// we charge also headerDelay.
Tick snoop_resp_time = clockEdge(forwardLatency) + pkt->headerDelay;
// Reset the timing of the packet.
pkt->headerDelay = pkt->payloadDelay = 0;
memSidePort->schedTimingSnoopResp(pkt, snoop_resp_time);
}
void
Cache::promoteWholeLineWrites(PacketPtr pkt)
{
// Cache line clearing instructions
if (doFastWrites && (pkt->cmd == MemCmd::WriteReq) &&
(pkt->getSize() == blkSize) && (pkt->getOffset(blkSize) == 0)) {
pkt->cmd = MemCmd::WriteLineReq;
DPRINTF(Cache, "packet promoted from Write to WriteLineReq\n");
}
}
bool
Cache::recvTimingReq(PacketPtr pkt)
{
DPRINTF(CacheTags, "%s tags:\n%s\n", __func__, tags->print());
assert(pkt->isRequest());
// Just forward the packet if caches are disabled.
if (system->bypassCaches()) {
// @todo This should really enqueue the packet rather
bool M5_VAR_USED success = memSidePort->sendTimingReq(pkt);
assert(success);
return true;
}
promoteWholeLineWrites(pkt);
// Cache maintenance operations have to visit all the caches down
// to the specified xbar (PoC, PoU, etc.). Even if a cache above
// is responding we forward the packet to the memory below rather
// than creating an express snoop.
if (pkt->cacheResponding()) {
// a cache above us (but not where the packet came from) is
// responding to the request, in other words it has the line
// in Modified or Owned state
DPRINTF(Cache, "Cache above responding to %s: not responding\n",
pkt->print());
// if the packet needs the block to be writable, and the cache
// that has promised to respond (setting the cache responding
// flag) is not providing writable (it is in Owned rather than
// the Modified state), we know that there may be other Shared
// copies in the system; go out and invalidate them all
assert(pkt->needsWritable() && !pkt->responderHadWritable());
// an upstream cache that had the line in Owned state
// (dirty, but not writable), is responding and thus
// transferring the dirty line from one branch of the
// cache hierarchy to another
// send out an express snoop and invalidate all other
// copies (snooping a packet that needs writable is the
// same as an invalidation), thus turning the Owned line
// into a Modified line, note that we don't invalidate the
// block in the current cache or any other cache on the
// path to memory
// create a downstream express snoop with cleared packet
// flags, there is no need to allocate any data as the
// packet is merely used to co-ordinate state transitions
Packet *snoop_pkt = new Packet(pkt, true, false);
// also reset the bus time that the original packet has
// not yet paid for
snoop_pkt->headerDelay = snoop_pkt->payloadDelay = 0;
// make this an instantaneous express snoop, and let the
// other caches in the system know that the another cache
// is responding, because we have found the authorative
// copy (Modified or Owned) that will supply the right
// data
snoop_pkt->setExpressSnoop();
snoop_pkt->setCacheResponding();
// this express snoop travels towards the memory, and at
// every crossbar it is snooped upwards thus reaching
// every cache in the system
bool M5_VAR_USED success = memSidePort->sendTimingReq(snoop_pkt);
// express snoops always succeed
assert(success);
// main memory will delete the snoop packet
// queue for deletion, as opposed to immediate deletion, as
// the sending cache is still relying on the packet
pendingDelete.reset(pkt);
// no need to take any further action in this particular cache
// as an upstram cache has already committed to responding,
// and we have already sent out any express snoops in the
// section above to ensure all other copies in the system are
// invalidated
return true;
}
// anything that is merely forwarded pays for the forward latency and
// the delay provided by the crossbar
Tick forward_time = clockEdge(forwardLatency) + pkt->headerDelay;
// We use lookupLatency here because it is used to specify the latency
// to access.
Cycles lat = lookupLatency;
CacheBlk *blk = nullptr;
bool satisfied = false;
{
PacketList writebacks;
// Note that lat is passed by reference here. The function
// access() calls accessBlock() which can modify lat value.
satisfied = access(pkt, blk, lat, writebacks);
// copy writebacks to write buffer here to ensure they logically
// proceed anything happening below
doWritebacks(writebacks, forward_time);
}
// Here we charge the headerDelay that takes into account the latencies
// of the bus, if the packet comes from it.
// The latency charged it is just lat that is the value of lookupLatency
// modified by access() function, or if not just lookupLatency.
// In case of a hit we are neglecting response latency.
// In case of a miss we are neglecting forward latency.
Tick request_time = clockEdge(lat) + pkt->headerDelay;
// Here we reset the timing of the packet.
pkt->headerDelay = pkt->payloadDelay = 0;
// track time of availability of next prefetch, if any
Tick next_pf_time = MaxTick;
bool needsResponse = pkt->needsResponse();
if (satisfied) {
// should never be satisfying an uncacheable access as we
// flush and invalidate any existing block as part of the
// lookup
assert(!pkt->req->isUncacheable());
// hit (for all other request types)
if (prefetcher && (prefetchOnAccess ||
(blk && blk->wasPrefetched()))) {
if (blk)
blk->status &= ~BlkHWPrefetched;
// Don't notify on SWPrefetch
if (!pkt->cmd.isSWPrefetch()) {
assert(!pkt->req->isCacheMaintenance());
next_pf_time = prefetcher->notify(pkt);
}
}
if (needsResponse) {
pkt->makeTimingResponse();
// @todo: Make someone pay for this
pkt->headerDelay = pkt->payloadDelay = 0;
// In this case we are considering request_time that takes
// into account the delay of the xbar, if any, and just
// lat, neglecting responseLatency, modelling hit latency
// just as lookupLatency or or the value of lat overriden
// by access(), that calls accessBlock() function.
cpuSidePort->schedTimingResp(pkt, request_time, true);
} else {
DPRINTF(Cache, "%s satisfied %s, no response needed\n", __func__,
pkt->print());
// queue the packet for deletion, as the sending cache is
// still relying on it; if the block is found in access(),
// CleanEvict and Writeback messages will be deleted
// here as well
pendingDelete.reset(pkt);
}
} else {
// miss
Addr blk_addr = pkt->getBlockAddr(blkSize);
// ignore any existing MSHR if we are dealing with an
// uncacheable request
MSHR *mshr = pkt->req->isUncacheable() ? nullptr :
mshrQueue.findMatch(blk_addr, pkt->isSecure());
// Software prefetch handling:
// To keep the core from waiting on data it won't look at
// anyway, send back a response with dummy data. Miss handling
// will continue asynchronously. Unfortunately, the core will
// insist upon freeing original Packet/Request, so we have to
// create a new pair with a different lifecycle. Note that this
// processing happens before any MSHR munging on the behalf of
// this request because this new Request will be the one stored
// into the MSHRs, not the original.
if (pkt->cmd.isSWPrefetch()) {
assert(needsResponse);
assert(pkt->req->hasPaddr());
assert(!pkt->req->isUncacheable());
// There's no reason to add a prefetch as an additional target
// to an existing MSHR. If an outstanding request is already
// in progress, there is nothing for the prefetch to do.
// If this is the case, we don't even create a request at all.
PacketPtr pf = nullptr;
if (!mshr) {
// copy the request and create a new SoftPFReq packet
RequestPtr req = new Request(pkt->req->getPaddr(),
pkt->req->getSize(),
pkt->req->getFlags(),
pkt->req->masterId());
pf = new Packet(req, pkt->cmd);
pf->allocate();
assert(pf->getAddr() == pkt->getAddr());
assert(pf->getSize() == pkt->getSize());
}
pkt->makeTimingResponse();
// request_time is used here, taking into account lat and the delay
// charged if the packet comes from the xbar.
cpuSidePort->schedTimingResp(pkt, request_time, true);
// If an outstanding request is in progress (we found an
// MSHR) this is set to null
pkt = pf;
}
if (mshr) {
/// MSHR hit
/// @note writebacks will be checked in getNextMSHR()
/// for any conflicting requests to the same block
//@todo remove hw_pf here
// Coalesce unless it was a software prefetch (see above).
if (pkt) {
assert(!pkt->isWriteback());
// CleanEvicts corresponding to blocks which have
// outstanding requests in MSHRs are simply sunk here
if (pkt->cmd == MemCmd::CleanEvict) {
pendingDelete.reset(pkt);
} else if (pkt->cmd == MemCmd::WriteClean) {
// A WriteClean should never coalesce with any
// outstanding cache maintenance requests.
// We use forward_time here because there is an
// uncached memory write, forwarded to WriteBuffer.
allocateWriteBuffer(pkt, forward_time);
} else {
DPRINTF(Cache, "%s coalescing MSHR for %s\n", __func__,
pkt->print());
assert(pkt->req->masterId() < system->maxMasters());
mshr_hits[pkt->cmdToIndex()][pkt->req->masterId()]++;
// We use forward_time here because it is the same
// considering new targets. We have multiple
// requests for the same address here. It
// specifies the latency to allocate an internal
// buffer and to schedule an event to the queued
// port and also takes into account the additional
// delay of the xbar.
mshr->allocateTarget(pkt, forward_time, order++,
allocOnFill(pkt->cmd));
if (mshr->getNumTargets() == numTarget) {
noTargetMSHR = mshr;
setBlocked(Blocked_NoTargets);
// need to be careful with this... if this mshr isn't
// ready yet (i.e. time > curTick()), we don't want to
// move it ahead of mshrs that are ready
// mshrQueue.moveToFront(mshr);
}
}
// We should call the prefetcher reguardless if the request is
// satisfied or not, reguardless if the request is in the MSHR
// or not. The request could be a ReadReq hit, but still not
// satisfied (potentially because of a prior write to the same
// cache line. So, even when not satisfied, tehre is an MSHR
// already allocated for this, we need to let the prefetcher
// know about the request
if (prefetcher) {
// Don't notify on SWPrefetch
if (!pkt->cmd.isSWPrefetch() &&
!pkt->req->isCacheMaintenance())
next_pf_time = prefetcher->notify(pkt);
}
}
} else {
// no MSHR
assert(pkt->req->masterId() < system->maxMasters());
if (pkt->req->isUncacheable()) {
mshr_uncacheable[pkt->cmdToIndex()][pkt->req->masterId()]++;
} else {
mshr_misses[pkt->cmdToIndex()][pkt->req->masterId()]++;
}
if (pkt->isEviction() || pkt->cmd == MemCmd::WriteClean ||
(pkt->req->isUncacheable() && pkt->isWrite())) {
// We use forward_time here because there is an
// uncached memory write, forwarded to WriteBuffer.
allocateWriteBuffer(pkt, forward_time);
} else {
if (blk && blk->isValid()) {
// should have flushed and have no valid block
assert(!pkt->req->isUncacheable());
// If we have a write miss to a valid block, we
// need to mark the block non-readable. Otherwise
// if we allow reads while there's an outstanding
// write miss, the read could return stale data
// out of the cache block... a more aggressive
// system could detect the overlap (if any) and
// forward data out of the MSHRs, but we don't do
// that yet. Note that we do need to leave the
// block valid so that it stays in the cache, in
// case we get an upgrade response (and hence no
// new data) when the write miss completes.
// As long as CPUs do proper store/load forwarding
// internally, and have a sufficiently weak memory
// model, this is probably unnecessary, but at some
// point it must have seemed like we needed it...
assert((pkt->needsWritable() && !blk->isWritable()) ||
pkt->req->isCacheMaintenance());
blk->status &= ~BlkReadable;
}
// Here we are using forward_time, modelling the latency of
// a miss (outbound) just as forwardLatency, neglecting the
// lookupLatency component.
allocateMissBuffer(pkt, forward_time);
}
if (prefetcher) {
// Don't notify on SWPrefetch
if (!pkt->cmd.isSWPrefetch() &&
!pkt->req->isCacheMaintenance())
next_pf_time = prefetcher->notify(pkt);
}
}
}
if (next_pf_time != MaxTick)
schedMemSideSendEvent(next_pf_time);
return true;
}
PacketPtr
Cache::createMissPacket(PacketPtr cpu_pkt, CacheBlk *blk,
bool needsWritable) const
{
// should never see evictions here
assert(!cpu_pkt->isEviction());
bool blkValid = blk && blk->isValid();
if (cpu_pkt->req->isUncacheable() ||
(!blkValid && cpu_pkt->isUpgrade()) ||
cpu_pkt->cmd == MemCmd::InvalidateReq || cpu_pkt->isClean()) {
// uncacheable requests and upgrades from upper-level caches
// that missed completely just go through as is
return nullptr;
}
assert(cpu_pkt->needsResponse());
MemCmd cmd;
// @TODO make useUpgrades a parameter.
// Note that ownership protocols require upgrade, otherwise a
// write miss on a shared owned block will generate a ReadExcl,
// which will clobber the owned copy.
const bool useUpgrades = true;
if (cpu_pkt->cmd == MemCmd::WriteLineReq) {
assert(!blkValid || !blk->isWritable());
// forward as invalidate to all other caches, this gives us
// the line in Exclusive state, and invalidates all other
// copies
cmd = MemCmd::InvalidateReq;
} else if (blkValid && useUpgrades) {
// only reason to be here is that blk is read only and we need
// it to be writable
assert(needsWritable);
assert(!blk->isWritable());
cmd = cpu_pkt->isLLSC() ? MemCmd::SCUpgradeReq : MemCmd::UpgradeReq;
} else if (cpu_pkt->cmd == MemCmd::SCUpgradeFailReq ||
cpu_pkt->cmd == MemCmd::StoreCondFailReq) {
// Even though this SC will fail, we still need to send out the
// request and get the data to supply it to other snoopers in the case
// where the determination the StoreCond fails is delayed due to
// all caches not being on the same local bus.
cmd = MemCmd::SCUpgradeFailReq;
} else {
// block is invalid
// If the request does not need a writable there are two cases
// where we need to ensure the response will not fetch the
// block in dirty state:
// * this cache is read only and it does not perform
// writebacks,
// * this cache is mostly exclusive and will not fill (since
// it does not fill it will have to writeback the dirty data
// immediately which generates uneccesary writebacks).
bool force_clean_rsp = isReadOnly || clusivity == Enums::mostly_excl;
cmd = needsWritable ? MemCmd::ReadExReq :
(force_clean_rsp ? MemCmd::ReadCleanReq : MemCmd::ReadSharedReq);
}
PacketPtr pkt = new Packet(cpu_pkt->req, cmd, blkSize);
// if there are upstream caches that have already marked the
// packet as having sharers (not passing writable), pass that info
// downstream
if (cpu_pkt->hasSharers() && !needsWritable) {
// note that cpu_pkt may have spent a considerable time in the
// MSHR queue and that the information could possibly be out
// of date, however, there is no harm in conservatively
// assuming the block has sharers
pkt->setHasSharers();
DPRINTF(Cache, "%s: passing hasSharers from %s to %s\n",
__func__, cpu_pkt->print(), pkt->print());
}
// the packet should be block aligned
assert(pkt->getAddr() == pkt->getBlockAddr(blkSize));
pkt->allocate();
DPRINTF(Cache, "%s: created %s from %s\n", __func__, pkt->print(),
cpu_pkt->print());
return pkt;
}
Tick
Cache::recvAtomic(PacketPtr pkt)
{
// We are in atomic mode so we pay just for lookupLatency here.
Cycles lat = lookupLatency;
// Forward the request if the system is in cache bypass mode.
if (system->bypassCaches())
return ticksToCycles(memSidePort->sendAtomic(pkt));
promoteWholeLineWrites(pkt);
// follow the same flow as in recvTimingReq, and check if a cache
// above us is responding
if (pkt->cacheResponding() && !pkt->isClean()) {
assert(!pkt->req->isCacheInvalidate());
DPRINTF(Cache, "Cache above responding to %s: not responding\n",
pkt->print());
// if a cache is responding, and it had the line in Owned
// rather than Modified state, we need to invalidate any
// copies that are not on the same path to memory
assert(pkt->needsWritable() && !pkt->responderHadWritable());
lat += ticksToCycles(memSidePort->sendAtomic(pkt));
return lat * clockPeriod();
}
// should assert here that there are no outstanding MSHRs or
// writebacks... that would mean that someone used an atomic
// access in timing mode
CacheBlk *blk = nullptr;
PacketList writebacks;
bool satisfied = access(pkt, blk, lat, writebacks);
if (pkt->isClean() && blk && blk->isDirty()) {
// A cache clean opearation is looking for a dirty
// block. If a dirty block is encountered a WriteClean
// will update any copies to the path to the memory
// until the point of reference.
DPRINTF(CacheVerbose, "%s: packet %s found block: %s\n",
__func__, pkt->print(), blk->print());
PacketPtr wb_pkt = writecleanBlk(blk, pkt->req->getDest(), pkt->id);
writebacks.push_back(wb_pkt);
pkt->setSatisfied();
}
// handle writebacks resulting from the access here to ensure they
// logically proceed anything happening below
doWritebacksAtomic(writebacks);
if (!satisfied) {
// MISS
// deal with the packets that go through the write path of
// the cache, i.e. any evictions and writes
if (pkt->isEviction() || pkt->cmd == MemCmd::WriteClean ||
(pkt->req->isUncacheable() && pkt->isWrite())) {
lat += ticksToCycles(memSidePort->sendAtomic(pkt));
return lat * clockPeriod();
}
// only misses left
PacketPtr bus_pkt = createMissPacket(pkt, blk, pkt->needsWritable());
bool is_forward = (bus_pkt == nullptr);
if (is_forward) {
// just forwarding the same request to the next level
// no local cache operation involved
bus_pkt = pkt;
}
DPRINTF(Cache, "%s: Sending an atomic %s\n", __func__,
bus_pkt->print());
#if TRACING_ON
CacheBlk::State old_state = blk ? blk->status : 0;
#endif
lat += ticksToCycles(memSidePort->sendAtomic(bus_pkt));
bool is_invalidate = bus_pkt->isInvalidate();
// We are now dealing with the response handling
DPRINTF(Cache, "%s: Receive response: %s in state %i\n", __func__,
bus_pkt->print(), old_state);
// If packet was a forward, the response (if any) is already
// in place in the bus_pkt == pkt structure, so we don't need
// to do anything. Otherwise, use the separate bus_pkt to
// generate response to pkt and then delete it.
if (!is_forward) {
if (pkt->needsResponse()) {
assert(bus_pkt->isResponse());
if (bus_pkt->isError()) {
pkt->makeAtomicResponse();
pkt->copyError(bus_pkt);
} else if (pkt->cmd == MemCmd::WriteLineReq) {
// note the use of pkt, not bus_pkt here.
// write-line request to the cache that promoted
// the write to a whole line
blk = handleFill(pkt, blk, writebacks,
allocOnFill(pkt->cmd));
assert(blk != NULL);
is_invalidate = false;
satisfyRequest(pkt, blk);
} else if (bus_pkt->isRead() ||
bus_pkt->cmd == MemCmd::UpgradeResp) {
// we're updating cache state to allow us to
// satisfy the upstream request from the cache
blk = handleFill(bus_pkt, blk, writebacks,
allocOnFill(pkt->cmd));
satisfyRequest(pkt, blk);
maintainClusivity(pkt->fromCache(), blk);
} else {
// we're satisfying the upstream request without
// modifying cache state, e.g., a write-through
pkt->makeAtomicResponse();
}
}
delete bus_pkt;
}
if (is_invalidate && blk && blk->isValid()) {
invalidateBlock(blk);
}
}
// Note that we don't invoke the prefetcher at all in atomic mode.
// It's not clear how to do it properly, particularly for
// prefetchers that aggressively generate prefetch candidates and
// rely on bandwidth contention to throttle them; these will tend
// to pollute the cache in atomic mode since there is no bandwidth
// contention. If we ever do want to enable prefetching in atomic
// mode, though, this is the place to do it... see timingAccess()
// for an example (though we'd want to issue the prefetch(es)
// immediately rather than calling requestMemSideBus() as we do
// there).
// do any writebacks resulting from the response handling
doWritebacksAtomic(writebacks);
// if we used temp block, check to see if its valid and if so
// clear it out, but only do so after the call to recvAtomic is
// finished so that any downstream observers (such as a snoop
// filter), first see the fill, and only then see the eviction
if (blk == tempBlock && tempBlock->isValid()) {
// the atomic CPU calls recvAtomic for fetch and load/store
// sequentuially, and we may already have a tempBlock
// writeback from the fetch that we have not yet sent
if (tempBlockWriteback) {
// if that is the case, write the prevoius one back, and
// do not schedule any new event
writebackTempBlockAtomic();
} else {
// the writeback/clean eviction happens after the call to
// recvAtomic has finished (but before any successive
// calls), so that the response handling from the fill is
// allowed to happen first
schedule(writebackTempBlockAtomicEvent, curTick());
}
tempBlockWriteback = (blk->isDirty() || writebackClean) ?
writebackBlk(blk) : cleanEvictBlk(blk);
invalidateBlock(blk);
}
if (pkt->needsResponse()) {
pkt->makeAtomicResponse();
}
return lat * clockPeriod();
}
void
Cache::functionalAccess(PacketPtr pkt, bool fromCpuSide)
{
if (system->bypassCaches()) {
// Packets from the memory side are snoop request and
// shouldn't happen in bypass mode.
assert(fromCpuSide);
// The cache should be flushed if we are in cache bypass mode,
// so we don't need to check if we need to update anything.
memSidePort->sendFunctional(pkt);
return;
}
Addr blk_addr = pkt->getBlockAddr(blkSize);
bool is_secure = pkt->isSecure();
CacheBlk *blk = tags->findBlock(pkt->getAddr(), is_secure);
MSHR *mshr = mshrQueue.findMatch(blk_addr, is_secure);
pkt->pushLabel(name());
CacheBlkPrintWrapper cbpw(blk);
// Note that just because an L2/L3 has valid data doesn't mean an
// L1 doesn't have a more up-to-date modified copy that still
// needs to be found. As a result we always update the request if
// we have it, but only declare it satisfied if we are the owner.
// see if we have data at all (owned or otherwise)
bool have_data = blk && blk->isValid()
&& pkt->checkFunctional(&cbpw, blk_addr, is_secure, blkSize,
blk->data);
// data we have is dirty if marked as such or if we have an
// in-service MSHR that is pending a modified line
bool have_dirty =
have_data && (blk->isDirty() ||
(mshr && mshr->inService && mshr->isPendingModified()));
bool done = have_dirty
|| cpuSidePort->checkFunctional(pkt)
|| mshrQueue.checkFunctional(pkt, blk_addr)
|| writeBuffer.checkFunctional(pkt, blk_addr)
|| memSidePort->checkFunctional(pkt);
DPRINTF(CacheVerbose, "%s: %s %s%s%s\n", __func__, pkt->print(),
(blk && blk->isValid()) ? "valid " : "",
have_data ? "data " : "", done ? "done " : "");
// We're leaving the cache, so pop cache->name() label
pkt->popLabel();
if (done) {
pkt->makeResponse();
} else {
// if it came as a request from the CPU side then make sure it
// continues towards the memory side
if (fromCpuSide) {
memSidePort->sendFunctional(pkt);
} else if (cpuSidePort->isSnooping()) {
// if it came from the memory side, it must be a snoop request
// and we should only forward it if we are forwarding snoops
cpuSidePort->sendFunctionalSnoop(pkt);
}
}
}
/////////////////////////////////////////////////////
//
// Response handling: responses from the memory side
//
/////////////////////////////////////////////////////
void
Cache::handleUncacheableWriteResp(PacketPtr pkt)
{
Tick completion_time = clockEdge(responseLatency) +
pkt->headerDelay + pkt->payloadDelay;
// Reset the bus additional time as it is now accounted for
pkt->headerDelay = pkt->payloadDelay = 0;
cpuSidePort->schedTimingResp(pkt, completion_time, true);
}
void
Cache::recvTimingResp(PacketPtr pkt)
{
assert(pkt->isResponse());
// all header delay should be paid for by the crossbar, unless
// this is a prefetch response from above
panic_if(pkt->headerDelay != 0 && pkt->cmd != MemCmd::HardPFResp,
"%s saw a non-zero packet delay\n", name());
bool is_error = pkt->isError();
if (is_error) {
DPRINTF(Cache, "%s: Cache received %s with error\n", __func__,
pkt->print());
}
DPRINTF(Cache, "%s: Handling response %s\n", __func__,
pkt->print());
// if this is a write, we should be looking at an uncacheable
// write
if (pkt->isWrite()) {
assert(pkt->req->isUncacheable());
handleUncacheableWriteResp(pkt);
return;
}
// we have dealt with any (uncacheable) writes above, from here on
// we know we are dealing with an MSHR due to a miss or a prefetch
MSHR *mshr = dynamic_cast<MSHR*>(pkt->popSenderState());
assert(mshr);
if (mshr == noTargetMSHR) {
// we always clear at least one target
clearBlocked(Blocked_NoTargets);
noTargetMSHR = nullptr;
}
// Initial target is used just for stats
MSHR::Target *initial_tgt = mshr->getTarget();
int stats_cmd_idx = initial_tgt->pkt->cmdToIndex();
Tick miss_latency = curTick() - initial_tgt->recvTime;
if (pkt->req->isUncacheable()) {
assert(pkt->req->masterId() < system->maxMasters());
mshr_uncacheable_lat[stats_cmd_idx][pkt->req->masterId()] +=
miss_latency;
} else {
assert(pkt->req->masterId() < system->maxMasters());
mshr_miss_latency[stats_cmd_idx][pkt->req->masterId()] +=
miss_latency;
}
bool wasFull = mshrQueue.isFull();
PacketList writebacks;
Tick forward_time = clockEdge(forwardLatency) + pkt->headerDelay;
bool is_fill = !mshr->isForward &&
(pkt->isRead() || pkt->cmd == MemCmd::UpgradeResp);
CacheBlk *blk = tags->findBlock(pkt->getAddr(), pkt->isSecure());
const bool valid_blk = blk && blk->isValid();
// If the response indicates that there are no sharers and we
// either had the block already or the response is filling we can
// promote our copy to writable
if (!pkt->hasSharers() &&
(is_fill || (valid_blk && !pkt->req->isCacheInvalidate()))) {
mshr->promoteWritable();
}
if (is_fill && !is_error) {
DPRINTF(Cache, "Block for addr %#llx being updated in Cache\n",
pkt->getAddr());
blk = handleFill(pkt, blk, writebacks, mshr->allocOnFill());
assert(blk != nullptr);
}
// allow invalidation responses originating from write-line
// requests to be discarded
bool is_invalidate = pkt->isInvalidate();
// The block was marked as not readable while there was a pending
// cache maintenance operation, restore its flag.
if (pkt->isClean() && !is_invalidate && valid_blk) {
blk->status |= BlkReadable;
}
// First offset for critical word first calculations
int initial_offset = initial_tgt->pkt->getOffset(blkSize);
bool from_cache = false;
MSHR::TargetList targets = mshr->extractServiceableTargets(pkt);
for (auto &target: targets) {
Packet *tgt_pkt = target.pkt;
switch (target.source) {
case MSHR::Target::FromCPU:
Tick completion_time;
// Here we charge on completion_time the delay of the xbar if the
// packet comes from it, charged on headerDelay.
completion_time = pkt->headerDelay;
// Software prefetch handling for cache closest to core
if (tgt_pkt->cmd.isSWPrefetch()) {
// a software prefetch would have already been ack'd
// immediately with dummy data so the core would be able to
// retire it. This request completes right here, so we
// deallocate it.
delete tgt_pkt->req;
delete tgt_pkt;
break; // skip response
}
// keep track of whether we have responded to another
// cache
from_cache = from_cache || tgt_pkt->fromCache();
// unlike the other packet flows, where data is found in other
// caches or memory and brought back, write-line requests always
// have the data right away, so the above check for "is fill?"
// cannot actually be determined until examining the stored MSHR
// state. We "catch up" with that logic here, which is duplicated
// from above.
if (tgt_pkt->cmd == MemCmd::WriteLineReq) {
assert(!is_error);
// we got the block in a writable state, so promote
// any deferred targets if possible
mshr->promoteWritable();
// NB: we use the original packet here and not the response!
blk = handleFill(tgt_pkt, blk, writebacks,
targets.allocOnFill);
assert(blk != nullptr);
// treat as a fill, and discard the invalidation
// response
is_fill = true;
is_invalidate = false;
}
if (is_fill) {
satisfyRequest(tgt_pkt, blk, true, mshr->hasPostDowngrade());
// How many bytes past the first request is this one
int transfer_offset =
tgt_pkt->getOffset(blkSize) - initial_offset;
if (transfer_offset < 0) {
transfer_offset += blkSize;
}
// If not critical word (offset) return payloadDelay.
// responseLatency is the latency of the return path
// from lower level caches/memory to an upper level cache or
// the core.
completion_time += clockEdge(responseLatency) +
(transfer_offset ? pkt->payloadDelay : 0);
assert(!tgt_pkt->req->isUncacheable());
assert(tgt_pkt->req->masterId() < system->maxMasters());
missLatency[tgt_pkt->cmdToIndex()][tgt_pkt->req->masterId()] +=
completion_time - target.recvTime;
} else if (pkt->cmd == MemCmd::UpgradeFailResp) {
// failed StoreCond upgrade
assert(tgt_pkt->cmd == MemCmd::StoreCondReq ||
tgt_pkt->cmd == MemCmd::StoreCondFailReq ||
tgt_pkt->cmd == MemCmd::SCUpgradeFailReq);
// responseLatency is the latency of the return path
// from lower level caches/memory to an upper level cache or
// the core.
completion_time += clockEdge(responseLatency) +
pkt->payloadDelay;
tgt_pkt->req->setExtraData(0);
} else {
// We are about to send a response to a cache above
// that asked for an invalidation; we need to
// invalidate our copy immediately as the most
// up-to-date copy of the block will now be in the
// cache above. It will also prevent this cache from
// responding (if the block was previously dirty) to
// snoops as they should snoop the caches above where
// they will get the response from.
if (is_invalidate && blk && blk->isValid()) {
invalidateBlock(blk);
}
// not a cache fill, just forwarding response
// responseLatency is the latency of the return path
// from lower level cahces/memory to the core.
completion_time += clockEdge(responseLatency) +
pkt->payloadDelay;
if (pkt->isRead() && !is_error) {
// sanity check
assert(pkt->getAddr() == tgt_pkt->getAddr());
assert(pkt->getSize() >= tgt_pkt->getSize());
tgt_pkt->setData(pkt->getConstPtr<uint8_t>());
}
}
tgt_pkt->makeTimingResponse();
// if this packet is an error copy that to the new packet
if (is_error)
tgt_pkt->copyError(pkt);
if (tgt_pkt->cmd == MemCmd::ReadResp &&
(is_invalidate || mshr->hasPostInvalidate())) {
// If intermediate cache got ReadRespWithInvalidate,
// propagate that. Response should not have
// isInvalidate() set otherwise.
tgt_pkt->cmd = MemCmd::ReadRespWithInvalidate;
DPRINTF(Cache, "%s: updated cmd to %s\n", __func__,
tgt_pkt->print());
}
// Reset the bus additional time as it is now accounted for
tgt_pkt->headerDelay = tgt_pkt->payloadDelay = 0;
cpuSidePort->schedTimingResp(tgt_pkt, completion_time, true);
break;
case MSHR::Target::FromPrefetcher:
assert(tgt_pkt->cmd == MemCmd::HardPFReq);
if (blk)
blk->status |= BlkHWPrefetched;
delete tgt_pkt->req;
delete tgt_pkt;
break;
case MSHR::Target::FromSnoop:
// I don't believe that a snoop can be in an error state
assert(!is_error);
// response to snoop request
DPRINTF(Cache, "processing deferred snoop...\n");
// If the response is invalidating, a snooping target can
// be satisfied if it is also invalidating. If the reponse is, not
// only invalidating, but more specifically an InvalidateResp and
// the MSHR was created due to an InvalidateReq then a cache above
// is waiting to satisfy a WriteLineReq. In this case even an
// non-invalidating snoop is added as a target here since this is
// the ordering point. When the InvalidateResp reaches this cache,
// the snooping target will snoop further the cache above with the
// WriteLineReq.
assert(!is_invalidate || pkt->cmd == MemCmd::InvalidateResp ||
pkt->req->isCacheMaintenance() ||
mshr->hasPostInvalidate());
handleSnoop(tgt_pkt, blk, true, true, mshr->hasPostInvalidate());
break;
default:
panic("Illegal target->source enum %d\n", target.source);
}
}
maintainClusivity(from_cache, blk);
if (blk && blk->isValid()) {
// an invalidate response stemming from a write line request
// should not invalidate the block, so check if the
// invalidation should be discarded
if (is_invalidate || mshr->hasPostInvalidate()) {
invalidateBlock(blk);
} else if (mshr->hasPostDowngrade()) {
blk->status &= ~BlkWritable;
}
}
if (mshr->promoteDeferredTargets()) {
// avoid later read getting stale data while write miss is
// outstanding.. see comment in timingAccess()
if (blk) {
blk->status &= ~BlkReadable;
}
mshrQueue.markPending(mshr);
schedMemSideSendEvent(clockEdge() + pkt->payloadDelay);
} else {
mshrQueue.deallocate(mshr);
if (wasFull && !mshrQueue.isFull()) {
clearBlocked(Blocked_NoMSHRs);
}
// Request the bus for a prefetch if this deallocation freed enough
// MSHRs for a prefetch to take place
if (prefetcher && mshrQueue.canPrefetch()) {
Tick next_pf_time = std::max(prefetcher->nextPrefetchReadyTime(),
clockEdge());
if (next_pf_time != MaxTick)
schedMemSideSendEvent(next_pf_time);
}
}
// reset the xbar additional timinig as it is now accounted for
pkt->headerDelay = pkt->payloadDelay = 0;
// copy writebacks to write buffer
doWritebacks(writebacks, forward_time);
// if we used temp block, check to see if its valid and then clear it out
if (blk == tempBlock && tempBlock->isValid()) {
// We use forwardLatency here because we are copying
// Writebacks/CleanEvicts to write buffer. It specifies the latency to
// allocate an internal buffer and to schedule an event to the
// queued port.
if (blk->isDirty() || writebackClean) {
PacketPtr wbPkt = writebackBlk(blk);
allocateWriteBuffer(wbPkt, forward_time);
// Set BLOCK_CACHED flag if cached above.
if (isCachedAbove(wbPkt))
wbPkt->setBlockCached();
} else {
PacketPtr wcPkt = cleanEvictBlk(blk);
// Check to see if block is cached above. If not allocate
// write buffer
if (isCachedAbove(wcPkt))
delete wcPkt;
else
allocateWriteBuffer(wcPkt, forward_time);
}
invalidateBlock(blk);
}
DPRINTF(CacheVerbose, "%s: Leaving with %s\n", __func__, pkt->print());
delete pkt;
}
PacketPtr
Cache::writebackBlk(CacheBlk *blk)
{
chatty_assert(!isReadOnly || writebackClean,
"Writeback from read-only cache");
assert(blk && blk->isValid() && (blk->isDirty() || writebackClean));
writebacks[Request::wbMasterId]++;
Request *req = new Request(tags->regenerateBlkAddr(blk->tag, blk->set),
blkSize, 0, Request::wbMasterId);
if (blk->isSecure())
req->setFlags(Request::SECURE);
req->taskId(blk->task_id);
blk->task_id= ContextSwitchTaskId::Unknown;
blk->tickInserted = curTick();
PacketPtr pkt =
new Packet(req, blk->isDirty() ?
MemCmd::WritebackDirty : MemCmd::WritebackClean);
DPRINTF(Cache, "Create Writeback %s writable: %d, dirty: %d\n",
pkt->print(), blk->isWritable(), blk->isDirty());
if (blk->isWritable()) {
// not asserting shared means we pass the block in modified
// state, mark our own block non-writeable
blk->status &= ~BlkWritable;
} else {
// we are in the Owned state, tell the receiver
pkt->setHasSharers();
}
// make sure the block is not marked dirty
blk->status &= ~BlkDirty;
pkt->allocate();
std::memcpy(pkt->getPtr<uint8_t>(), blk->data, blkSize);
return pkt;
}
PacketPtr
Cache::writecleanBlk(CacheBlk *blk, Request::Flags dest, PacketId id)
{
Request *req = new Request(tags->regenerateBlkAddr(blk->tag, blk->set),
blkSize, 0, Request::wbMasterId);
if (blk->isSecure()) {
req->setFlags(Request::SECURE);
}
req->taskId(blk->task_id);
blk->task_id = ContextSwitchTaskId::Unknown;
PacketPtr pkt = new Packet(req, MemCmd::WriteClean, blkSize, id);
DPRINTF(Cache, "Create %s writable: %d, dirty: %d\n", pkt->print(),
blk->isWritable(), blk->isDirty());
// make sure the block is not marked dirty
blk->status &= ~BlkDirty;
pkt->allocate();
// We inform the cache below that the block has sharers in the
// system as we retain our copy.
pkt->setHasSharers();
if (dest) {
req->setFlags(dest);
pkt->setWriteThrough();
}
std::memcpy(pkt->getPtr<uint8_t>(), blk->data, blkSize);
return pkt;
}
PacketPtr
Cache::cleanEvictBlk(CacheBlk *blk)
{
assert(!writebackClean);
assert(blk && blk->isValid() && !blk->isDirty());
// Creating a zero sized write, a message to the snoop filter
Request *req =
new Request(tags->regenerateBlkAddr(blk->tag, blk->set), blkSize, 0,
Request::wbMasterId);
if (blk->isSecure())
req->setFlags(Request::SECURE);
req->taskId(blk->task_id);
blk->task_id = ContextSwitchTaskId::Unknown;
blk->tickInserted = curTick();
PacketPtr pkt = new Packet(req, MemCmd::CleanEvict);
pkt->allocate();
DPRINTF(Cache, "Create CleanEvict %s\n", pkt->print());
return pkt;
}
void
Cache::memWriteback()
{
CacheBlkVisitorWrapper visitor(*this, &Cache::writebackVisitor);
tags->forEachBlk(visitor);
}
void
Cache::memInvalidate()
{
CacheBlkVisitorWrapper visitor(*this, &Cache::invalidateVisitor);
tags->forEachBlk(visitor);
}
bool
Cache::isDirty() const
{
CacheBlkIsDirtyVisitor visitor;
tags->forEachBlk(visitor);
return visitor.isDirty();
}
bool
Cache::writebackVisitor(CacheBlk &blk)
{
if (blk.isDirty()) {
assert(blk.isValid());
Request request(tags->regenerateBlkAddr(blk.tag, blk.set),
blkSize, 0, Request::funcMasterId);
request.taskId(blk.task_id);
if (blk.isSecure()) {
request.setFlags(Request::SECURE);
}
Packet packet(&request, MemCmd::WriteReq);
packet.dataStatic(blk.data);
memSidePort->sendFunctional(&packet);
blk.status &= ~BlkDirty;
}
return true;
}
bool
Cache::invalidateVisitor(CacheBlk &blk)
{
if (blk.isDirty())
warn_once("Invalidating dirty cache lines. Expect things to break.\n");
if (blk.isValid()) {
assert(!blk.isDirty());
invalidateBlock(&blk);
}
return true;
}
CacheBlk*
Cache::allocateBlock(Addr addr, bool is_secure, PacketList &writebacks)
{
CacheBlk *blk = tags->findVictim(addr);
// It is valid to return nullptr if there is no victim
if (!blk)
return nullptr;
if (blk->isValid()) {
Addr repl_addr = tags->regenerateBlkAddr(blk->tag, blk->set);
MSHR *repl_mshr = mshrQueue.findMatch(repl_addr, blk->isSecure());
if (repl_mshr) {
// must be an outstanding upgrade request
// on a block we're about to replace...
assert(!blk->isWritable() || blk->isDirty());
assert(repl_mshr->needsWritable());
// too hard to replace block with transient state
// allocation failed, block not inserted
return nullptr;
} else {
DPRINTF(Cache, "replacement: replacing %#llx (%s) with %#llx "
"(%s): %s\n", repl_addr, blk->isSecure() ? "s" : "ns",
addr, is_secure ? "s" : "ns",
blk->isDirty() ? "writeback" : "clean");
if (blk->wasPrefetched()) {
unusedPrefetches++;
}
// Will send up Writeback/CleanEvict snoops via isCachedAbove
// when pushing this writeback list into the write buffer.
if (blk->isDirty() || writebackClean) {
// Save writeback packet for handling by caller
writebacks.push_back(writebackBlk(blk));
} else {
writebacks.push_back(cleanEvictBlk(blk));
}
}
}
return blk;
}
void
Cache::invalidateBlock(CacheBlk *blk)
{
if (blk != tempBlock)
tags->invalidate(blk);
blk->invalidate();
}
// Note that the reason we return a list of writebacks rather than
// inserting them directly in the write buffer is that this function
// is called by both atomic and timing-mode accesses, and in atomic
// mode we don't mess with the write buffer (we just perform the
// writebacks atomically once the original request is complete).
CacheBlk*
Cache::handleFill(PacketPtr pkt, CacheBlk *blk, PacketList &writebacks,
bool allocate)
{
assert(pkt->isResponse() || pkt->cmd == MemCmd::WriteLineReq);
Addr addr = pkt->getAddr();
bool is_secure = pkt->isSecure();
#if TRACING_ON
CacheBlk::State old_state = blk ? blk->status : 0;
#endif
// When handling a fill, we should have no writes to this line.
assert(addr == pkt->getBlockAddr(blkSize));
assert(!writeBuffer.findMatch(addr, is_secure));
if (blk == nullptr) {
// better have read new data...
assert(pkt->hasData());
// only read responses and write-line requests have data;
// note that we don't write the data here for write-line - that
// happens in the subsequent call to satisfyRequest
assert(pkt->isRead() || pkt->cmd == MemCmd::WriteLineReq);
// need to do a replacement if allocating, otherwise we stick
// with the temporary storage
blk = allocate ? allocateBlock(addr, is_secure, writebacks) : nullptr;
if (blk == nullptr) {
// No replaceable block or a mostly exclusive
// cache... just use temporary storage to complete the
// current request and then get rid of it
assert(!tempBlock->isValid());
blk = tempBlock;
tempBlock->set = tags->extractSet(addr);
tempBlock->tag = tags->extractTag(addr);
// @todo: set security state as well...
DPRINTF(Cache, "using temp block for %#llx (%s)\n", addr,
is_secure ? "s" : "ns");
} else {
tags->insertBlock(pkt, blk);
}
// we should never be overwriting a valid block
assert(!blk->isValid());
} else {
// existing block... probably an upgrade
assert(blk->tag == tags->extractTag(addr));
// either we're getting new data or the block should already be valid
assert(pkt->hasData() || blk->isValid());
// don't clear block status... if block is already dirty we
// don't want to lose that
}
if (is_secure)
blk->status |= BlkSecure;
blk->status |= BlkValid | BlkReadable;
// sanity check for whole-line writes, which should always be
// marked as writable as part of the fill, and then later marked
// dirty as part of satisfyRequest
if (pkt->cmd == MemCmd::WriteLineReq) {
assert(!pkt->hasSharers());
}
// here we deal with setting the appropriate state of the line,
// and we start by looking at the hasSharers flag, and ignore the
// cacheResponding flag (normally signalling dirty data) if the
// packet has sharers, thus the line is never allocated as Owned
// (dirty but not writable), and always ends up being either
// Shared, Exclusive or Modified, see Packet::setCacheResponding
// for more details
if (!pkt->hasSharers()) {
// we could get a writable line from memory (rather than a
// cache) even in a read-only cache, note that we set this bit
// even for a read-only cache, possibly revisit this decision
blk->status |= BlkWritable;
// check if we got this via cache-to-cache transfer (i.e., from a
// cache that had the block in Modified or Owned state)
if (pkt->cacheResponding()) {
// we got the block in Modified state, and invalidated the
// owners copy
blk->status |= BlkDirty;
chatty_assert(!isReadOnly, "Should never see dirty snoop response "
"in read-only cache %s\n", name());
}
}
DPRINTF(Cache, "Block addr %#llx (%s) moving from state %x to %s\n",
addr, is_secure ? "s" : "ns", old_state, blk->print());
// if we got new data, copy it in (checking for a read response
// and a response that has data is the same in the end)
if (pkt->isRead()) {
// sanity checks
assert(pkt->hasData());
assert(pkt->getSize() == blkSize);
std::memcpy(blk->data, pkt->getConstPtr<uint8_t>(), blkSize);
}
// We pay for fillLatency here.
blk->whenReady = clockEdge() + fillLatency * clockPeriod() +
pkt->payloadDelay;
return blk;
}
/////////////////////////////////////////////////////
//
// Snoop path: requests coming in from the memory side
//
/////////////////////////////////////////////////////
void
Cache::doTimingSupplyResponse(PacketPtr req_pkt, const uint8_t *blk_data,
bool already_copied, bool pending_inval)
{
// sanity check
assert(req_pkt->isRequest());
assert(req_pkt->needsResponse());
DPRINTF(Cache, "%s: for %s\n", __func__, req_pkt->print());
// timing-mode snoop responses require a new packet, unless we
// already made a copy...
PacketPtr pkt = req_pkt;
if (!already_copied)
// do not clear flags, and allocate space for data if the
// packet needs it (the only packets that carry data are read
// responses)
pkt = new Packet(req_pkt, false, req_pkt->isRead());
assert(req_pkt->req->isUncacheable() || req_pkt->isInvalidate() ||
pkt->hasSharers());
pkt->makeTimingResponse();
if (pkt->isRead()) {
pkt->setDataFromBlock(blk_data, blkSize);
}
if (pkt->cmd == MemCmd::ReadResp && pending_inval) {
// Assume we defer a response to a read from a far-away cache
// A, then later defer a ReadExcl from a cache B on the same
// bus as us. We'll assert cacheResponding in both cases, but
// in the latter case cacheResponding will keep the
// invalidation from reaching cache A. This special response
// tells cache A that it gets the block to satisfy its read,
// but must immediately invalidate it.
pkt->cmd = MemCmd::ReadRespWithInvalidate;
}
// Here we consider forward_time, paying for just forward latency and
// also charging the delay provided by the xbar.
// forward_time is used as send_time in next allocateWriteBuffer().
Tick forward_time = clockEdge(forwardLatency) + pkt->headerDelay;
// Here we reset the timing of the packet.
pkt->headerDelay = pkt->payloadDelay = 0;
DPRINTF(CacheVerbose, "%s: created response: %s tick: %lu\n", __func__,
pkt->print(), forward_time);
memSidePort->schedTimingSnoopResp(pkt, forward_time, true);
}
uint32_t
Cache::handleSnoop(PacketPtr pkt, CacheBlk *blk, bool is_timing,
bool is_deferred, bool pending_inval)
{
DPRINTF(CacheVerbose, "%s: for %s\n", __func__, pkt->print());
// deferred snoops can only happen in timing mode
assert(!(is_deferred && !is_timing));
// pending_inval only makes sense on deferred snoops
assert(!(pending_inval && !is_deferred));
assert(pkt->isRequest());
// the packet may get modified if we or a forwarded snooper
// responds in atomic mode, so remember a few things about the
// original packet up front
bool invalidate = pkt->isInvalidate();
bool M5_VAR_USED needs_writable = pkt->needsWritable();
// at the moment we could get an uncacheable write which does not
// have the invalidate flag, and we need a suitable way of dealing
// with this case
panic_if(invalidate && pkt->req->isUncacheable(),
"%s got an invalidating uncacheable snoop request %s",
name(), pkt->print());
uint32_t snoop_delay = 0;
if (forwardSnoops) {
// first propagate snoop upward to see if anyone above us wants to
// handle it. save & restore packet src since it will get
// rewritten to be relative to cpu-side bus (if any)
bool alreadyResponded = pkt->cacheResponding();
if (is_timing) {
// copy the packet so that we can clear any flags before
// forwarding it upwards, we also allocate data (passing
// the pointer along in case of static data), in case
// there is a snoop hit in upper levels
Packet snoopPkt(pkt, true, true);
snoopPkt.setExpressSnoop();
// the snoop packet does not need to wait any additional
// time
snoopPkt.headerDelay = snoopPkt.payloadDelay = 0;
cpuSidePort->sendTimingSnoopReq(&snoopPkt);
// add the header delay (including crossbar and snoop
// delays) of the upward snoop to the snoop delay for this
// cache
snoop_delay += snoopPkt.headerDelay;
if (snoopPkt.cacheResponding()) {
// cache-to-cache response from some upper cache
assert(!alreadyResponded);
pkt->setCacheResponding();
}
// upstream cache has the block, or has an outstanding
// MSHR, pass the flag on
if (snoopPkt.hasSharers()) {
pkt->setHasSharers();
}
// If this request is a prefetch or clean evict and an upper level
// signals block present, make sure to propagate the block
// presence to the requester.
if (snoopPkt.isBlockCached()) {
pkt->setBlockCached();
}
// If the request was satisfied by snooping the cache
// above, mark the original packet as satisfied too.
if (snoopPkt.satisfied()) {
pkt->setSatisfied();
}
} else {
cpuSidePort->sendAtomicSnoop(pkt);
if (!alreadyResponded && pkt->cacheResponding()) {
// cache-to-cache response from some upper cache:
// forward response to original requester
assert(pkt->isResponse());
}
}
}
bool respond = false;
bool blk_valid = blk && blk->isValid();
if (pkt->isClean()) {
if (blk_valid && blk->isDirty()) {
DPRINTF(CacheVerbose, "%s: packet (snoop) %s found block: %s\n",
__func__, pkt->print(), blk->print());
PacketPtr wb_pkt = writecleanBlk(blk, pkt->req->getDest(), pkt->id);
PacketList writebacks;
writebacks.push_back(wb_pkt);
if (is_timing) {
// anything that is merely forwarded pays for the forward
// latency and the delay provided by the crossbar
Tick forward_time = clockEdge(forwardLatency) +
pkt->headerDelay;
doWritebacks(writebacks, forward_time);
} else {
doWritebacksAtomic(writebacks);
}
pkt->setSatisfied();
}
} else if (!blk_valid) {
DPRINTF(CacheVerbose, "%s: snoop miss for %s\n", __func__,
pkt->print());
if (is_deferred) {
// we no longer have the block, and will not respond, but a
// packet was allocated in MSHR::handleSnoop and we have
// to delete it
assert(pkt->needsResponse());
// we have passed the block to a cache upstream, that
// cache should be responding
assert(pkt->cacheResponding());
delete pkt;
}
return snoop_delay;
} else {
DPRINTF(Cache, "%s: snoop hit for %s, old state is %s\n", __func__,
pkt->print(), blk->print());
// We may end up modifying both the block state and the packet (if
// we respond in atomic mode), so just figure out what to do now
// and then do it later. We respond to all snoops that need
// responses provided we have the block in dirty state. The
// invalidation itself is taken care of below. We don't respond to
// cache maintenance operations as this is done by the destination
// xbar.
respond = blk->isDirty() && pkt->needsResponse();
chatty_assert(!(isReadOnly && blk->isDirty()), "Should never have "
"a dirty block in a read-only cache %s\n", name());
}
// Invalidate any prefetch's from below that would strip write permissions
// MemCmd::HardPFReq is only observed by upstream caches. After missing
// above and in it's own cache, a new MemCmd::ReadReq is created that
// downstream caches observe.
if (pkt->mustCheckAbove()) {
DPRINTF(Cache, "Found addr %#llx in upper level cache for snoop %s "
"from lower cache\n", pkt->getAddr(), pkt->print());
pkt->setBlockCached();
return snoop_delay;
}
if (pkt->isRead() && !invalidate) {
// reading without requiring the line in a writable state
assert(!needs_writable);
pkt->setHasSharers();
// if the requesting packet is uncacheable, retain the line in
// the current state, otherwhise unset the writable flag,
// which means we go from Modified to Owned (and will respond
// below), remain in Owned (and will respond below), from
// Exclusive to Shared, or remain in Shared
if (!pkt->req->isUncacheable())
blk->status &= ~BlkWritable;
DPRINTF(Cache, "new state is %s\n", blk->print());
}
if (respond) {
// prevent anyone else from responding, cache as well as
// memory, and also prevent any memory from even seeing the
// request
pkt->setCacheResponding();
if (!pkt->isClean() && blk->isWritable()) {
// inform the cache hierarchy that this cache had the line
// in the Modified state so that we avoid unnecessary
// invalidations (see Packet::setResponderHadWritable)
pkt->setResponderHadWritable();
// in the case of an uncacheable request there is no point
// in setting the responderHadWritable flag, but since the
// recipient does not care there is no harm in doing so
} else {
// if the packet has needsWritable set we invalidate our
// copy below and all other copies will be invalidates
// through express snoops, and if needsWritable is not set
// we already called setHasSharers above
}
// if we are returning a writable and dirty (Modified) line,
// we should be invalidating the line
panic_if(!invalidate && !pkt->hasSharers(),
"%s is passing a Modified line through %s, "
"but keeping the block", name(), pkt->print());
if (is_timing) {
doTimingSupplyResponse(pkt, blk->data, is_deferred, pending_inval);
} else {
pkt->makeAtomicResponse();
// packets such as upgrades do not actually have any data
// payload
if (pkt->hasData())
pkt->setDataFromBlock(blk->data, blkSize);
}
}
if (!respond && is_deferred) {
assert(pkt->needsResponse());
// if we copied the deferred packet with the intention to
// respond, but are not responding, then a cache above us must
// be, and we can use this as the indication of whether this
// is a packet where we created a copy of the request or not
if (!pkt->cacheResponding()) {
delete pkt->req;
}
delete pkt;
}
// Do this last in case it deallocates block data or something
// like that
if (blk_valid && invalidate) {
invalidateBlock(blk);
DPRINTF(Cache, "new state is %s\n", blk->print());
}
return snoop_delay;
}
void
Cache::recvTimingSnoopReq(PacketPtr pkt)
{
DPRINTF(CacheVerbose, "%s: for %s\n", __func__, pkt->print());
// Snoops shouldn't happen when bypassing caches
assert(!system->bypassCaches());
// no need to snoop requests that are not in range
if (!inRange(pkt->getAddr())) {
return;
}
bool is_secure = pkt->isSecure();
CacheBlk *blk = tags->findBlock(pkt->getAddr(), is_secure);
Addr blk_addr = pkt->getBlockAddr(blkSize);
MSHR *mshr = mshrQueue.findMatch(blk_addr, is_secure);
// Update the latency cost of the snoop so that the crossbar can
// account for it. Do not overwrite what other neighbouring caches
// have already done, rather take the maximum. The update is
// tentative, for cases where we return before an upward snoop
// happens below.
pkt->snoopDelay = std::max<uint32_t>(pkt->snoopDelay,
lookupLatency * clockPeriod());
// Inform request(Prefetch, CleanEvict or Writeback) from below of
// MSHR hit, set setBlockCached.
if (mshr && pkt->mustCheckAbove()) {
DPRINTF(Cache, "Setting block cached for %s from lower cache on "
"mshr hit\n", pkt->print());
pkt->setBlockCached();
return;
}
// Bypass any existing cache maintenance requests if the request
// has been satisfied already (i.e., the dirty block has been
// found).
if (mshr && pkt->req->isCacheMaintenance() && pkt->satisfied()) {
return;
}
// Let the MSHR itself track the snoop and decide whether we want
// to go ahead and do the regular cache snoop
if (mshr && mshr->handleSnoop(pkt, order++)) {
DPRINTF(Cache, "Deferring snoop on in-service MSHR to blk %#llx (%s)."
"mshrs: %s\n", blk_addr, is_secure ? "s" : "ns",
mshr->print());
if (mshr->getNumTargets() > numTarget)
warn("allocating bonus target for snoop"); //handle later
return;
}
//We also need to check the writeback buffers and handle those
WriteQueueEntry *wb_entry = writeBuffer.findMatch(blk_addr, is_secure);
if (wb_entry) {
DPRINTF(Cache, "Snoop hit in writeback to addr %#llx (%s)\n",
pkt->getAddr(), is_secure ? "s" : "ns");
// Expect to see only Writebacks and/or CleanEvicts here, both of
// which should not be generated for uncacheable data.
assert(!wb_entry->isUncacheable());
// There should only be a single request responsible for generating
// Writebacks/CleanEvicts.
assert(wb_entry->getNumTargets() == 1);
PacketPtr wb_pkt = wb_entry->getTarget()->pkt;
assert(wb_pkt->isEviction() || wb_pkt->cmd == MemCmd::WriteClean);
if (pkt->isEviction()) {
// if the block is found in the write queue, set the BLOCK_CACHED
// flag for Writeback/CleanEvict snoop. On return the snoop will
// propagate the BLOCK_CACHED flag in Writeback packets and prevent
// any CleanEvicts from travelling down the memory hierarchy.
pkt->setBlockCached();
DPRINTF(Cache, "%s: Squashing %s from lower cache on writequeue "
"hit\n", __func__, pkt->print());
return;
}
// conceptually writebacks are no different to other blocks in
// this cache, so the behaviour is modelled after handleSnoop,
// the difference being that instead of querying the block
// state to determine if it is dirty and writable, we use the
// command and fields of the writeback packet
bool respond = wb_pkt->cmd == MemCmd::WritebackDirty &&
pkt->needsResponse();
bool have_writable = !wb_pkt->hasSharers();
bool invalidate = pkt->isInvalidate();
if (!pkt->req->isUncacheable() && pkt->isRead() && !invalidate) {
assert(!pkt->needsWritable());
pkt->setHasSharers();
wb_pkt->setHasSharers();
}
if (respond) {
pkt->setCacheResponding();
if (have_writable) {
pkt->setResponderHadWritable();
}
doTimingSupplyResponse(pkt, wb_pkt->getConstPtr<uint8_t>(),
false, false);
}
if (invalidate && wb_pkt->cmd != MemCmd::WriteClean) {
// Invalidation trumps our writeback... discard here
// Note: markInService will remove entry from writeback buffer.
markInService(wb_entry);
delete wb_pkt;
}
}
// If this was a shared writeback, there may still be
// other shared copies above that require invalidation.
// We could be more selective and return here if the
// request is non-exclusive or if the writeback is
// exclusive.
uint32_t snoop_delay = handleSnoop(pkt, blk, true, false, false);
// Override what we did when we first saw the snoop, as we now
// also have the cost of the upwards snoops to account for
pkt->snoopDelay = std::max<uint32_t>(pkt->snoopDelay, snoop_delay +
lookupLatency * clockPeriod());
}
bool
Cache::CpuSidePort::recvTimingSnoopResp(PacketPtr pkt)
{
// Express snoop responses from master to slave, e.g., from L1 to L2
cache->recvTimingSnoopResp(pkt);
return true;
}
Tick
Cache::recvAtomicSnoop(PacketPtr pkt)
{
// Snoops shouldn't happen when bypassing caches
assert(!system->bypassCaches());
// no need to snoop requests that are not in range.
if (!inRange(pkt->getAddr())) {
return 0;
}
CacheBlk *blk = tags->findBlock(pkt->getAddr(), pkt->isSecure());
uint32_t snoop_delay = handleSnoop(pkt, blk, false, false, false);
return snoop_delay + lookupLatency * clockPeriod();
}
QueueEntry*
Cache::getNextQueueEntry()
{
// Check both MSHR queue and write buffer for potential requests,
// note that null does not mean there is no request, it could
// simply be that it is not ready
MSHR *miss_mshr = mshrQueue.getNext();
WriteQueueEntry *wq_entry = writeBuffer.getNext();
// If we got a write buffer request ready, first priority is a
// full write buffer, otherwise we favour the miss requests
if (wq_entry && (writeBuffer.isFull() || !miss_mshr)) {
// need to search MSHR queue for conflicting earlier miss.
MSHR *conflict_mshr =
mshrQueue.findPending(wq_entry->blkAddr,
wq_entry->isSecure);
if (conflict_mshr && conflict_mshr->order < wq_entry->order) {
// Service misses in order until conflict is cleared.
return conflict_mshr;
// @todo Note that we ignore the ready time of the conflict here
}
// No conflicts; issue write
return wq_entry;
} else if (miss_mshr) {
// need to check for conflicting earlier writeback
WriteQueueEntry *conflict_mshr =
writeBuffer.findPending(miss_mshr->blkAddr,
miss_mshr->isSecure);
if (conflict_mshr) {
// not sure why we don't check order here... it was in the
// original code but commented out.
// The only way this happens is if we are
// doing a write and we didn't have permissions
// then subsequently saw a writeback (owned got evicted)
// We need to make sure to perform the writeback first
// To preserve the dirty data, then we can issue the write
// should we return wq_entry here instead? I.e. do we
// have to flush writes in order? I don't think so... not
// for Alpha anyway. Maybe for x86?
return conflict_mshr;
// @todo Note that we ignore the ready time of the conflict here
}
// No conflicts; issue read
return miss_mshr;
}
// fall through... no pending requests. Try a prefetch.
assert(!miss_mshr && !wq_entry);
if (prefetcher && mshrQueue.canPrefetch()) {
// If we have a miss queue slot, we can try a prefetch
PacketPtr pkt = prefetcher->getPacket();
if (pkt) {
Addr pf_addr = pkt->getBlockAddr(blkSize);
if (!tags->findBlock(pf_addr, pkt->isSecure()) &&
!mshrQueue.findMatch(pf_addr, pkt->isSecure()) &&
!writeBuffer.findMatch(pf_addr, pkt->isSecure())) {
// Update statistic on number of prefetches issued
// (hwpf_mshr_misses)
assert(pkt->req->masterId() < system->maxMasters());
mshr_misses[pkt->cmdToIndex()][pkt->req->masterId()]++;
// allocate an MSHR and return it, note
// that we send the packet straight away, so do not
// schedule the send
return allocateMissBuffer(pkt, curTick(), false);
} else {
// free the request and packet
delete pkt->req;
delete pkt;
}
}
}
return nullptr;
}
bool
Cache::isCachedAbove(PacketPtr pkt, bool is_timing) const
{
if (!forwardSnoops)
return false;
// Mirroring the flow of HardPFReqs, the cache sends CleanEvict and
// Writeback snoops into upper level caches to check for copies of the
// same block. Using the BLOCK_CACHED flag with the Writeback/CleanEvict
// packet, the cache can inform the crossbar below of presence or absence
// of the block.
if (is_timing) {
Packet snoop_pkt(pkt, true, false);
snoop_pkt.setExpressSnoop();
// Assert that packet is either Writeback or CleanEvict and not a
// prefetch request because prefetch requests need an MSHR and may
// generate a snoop response.
assert(pkt->isEviction() || pkt->cmd == MemCmd::WriteClean);
snoop_pkt.senderState = nullptr;
cpuSidePort->sendTimingSnoopReq(&snoop_pkt);
// Writeback/CleanEvict snoops do not generate a snoop response.
assert(!(snoop_pkt.cacheResponding()));
return snoop_pkt.isBlockCached();
} else {
cpuSidePort->sendAtomicSnoop(pkt);
return pkt->isBlockCached();
}
}
Tick
Cache::nextQueueReadyTime() const
{
Tick nextReady = std::min(mshrQueue.nextReadyTime(),
writeBuffer.nextReadyTime());
// Don't signal prefetch ready time if no MSHRs available
// Will signal once enoguh MSHRs are deallocated
if (prefetcher && mshrQueue.canPrefetch()) {
nextReady = std::min(nextReady,
prefetcher->nextPrefetchReadyTime());
}
return nextReady;
}
bool
Cache::sendMSHRQueuePacket(MSHR* mshr)
{
assert(mshr);
// use request from 1st target
PacketPtr tgt_pkt = mshr->getTarget()->pkt;
DPRINTF(Cache, "%s: MSHR %s\n", __func__, tgt_pkt->print());
CacheBlk *blk = tags->findBlock(mshr->blkAddr, mshr->isSecure);
if (tgt_pkt->cmd == MemCmd::HardPFReq && forwardSnoops) {
// we should never have hardware prefetches to allocated
// blocks
assert(blk == nullptr);
// We need to check the caches above us to verify that
// they don't have a copy of this block in the dirty state
// at the moment. Without this check we could get a stale
// copy from memory that might get used in place of the
// dirty one.
Packet snoop_pkt(tgt_pkt, true, false);
snoop_pkt.setExpressSnoop();
// We are sending this packet upwards, but if it hits we will
// get a snoop response that we end up treating just like a
// normal response, hence it needs the MSHR as its sender
// state
snoop_pkt.senderState = mshr;
cpuSidePort->sendTimingSnoopReq(&snoop_pkt);
// Check to see if the prefetch was squashed by an upper cache (to
// prevent us from grabbing the line) or if a Check to see if a
// writeback arrived between the time the prefetch was placed in
// the MSHRs and when it was selected to be sent or if the
// prefetch was squashed by an upper cache.
// It is important to check cacheResponding before
// prefetchSquashed. If another cache has committed to
// responding, it will be sending a dirty response which will
// arrive at the MSHR allocated for this request. Checking the
// prefetchSquash first may result in the MSHR being
// prematurely deallocated.
if (snoop_pkt.cacheResponding()) {
auto M5_VAR_USED r = outstandingSnoop.insert(snoop_pkt.req);
assert(r.second);
// if we are getting a snoop response with no sharers it
// will be allocated as Modified
bool pending_modified_resp = !snoop_pkt.hasSharers();
markInService(mshr, pending_modified_resp);
DPRINTF(Cache, "Upward snoop of prefetch for addr"
" %#x (%s) hit\n",
tgt_pkt->getAddr(), tgt_pkt->isSecure()? "s": "ns");
return false;
}
if (snoop_pkt.isBlockCached()) {
DPRINTF(Cache, "Block present, prefetch squashed by cache. "
"Deallocating mshr target %#x.\n",
mshr->blkAddr);
// Deallocate the mshr target
if (mshrQueue.forceDeallocateTarget(mshr)) {
// Clear block if this deallocation resulted freed an
// mshr when all had previously been utilized
clearBlocked(Blocked_NoMSHRs);
}
// given that no response is expected, delete Request and Packet
delete tgt_pkt->req;
delete tgt_pkt;
return false;
}
}
// either a prefetch that is not present upstream, or a normal
// MSHR request, proceed to get the packet to send downstream
PacketPtr pkt = createMissPacket(tgt_pkt, blk, mshr->needsWritable());
mshr->isForward = (pkt == nullptr);
if (mshr->isForward) {
// not a cache block request, but a response is expected
// make copy of current packet to forward, keep current
// copy for response handling
pkt = new Packet(tgt_pkt, false, true);
assert(!pkt->isWrite());
}
// play it safe and append (rather than set) the sender state,
// as forwarded packets may already have existing state
pkt->pushSenderState(mshr);
if (pkt->isClean() && blk && blk->isDirty()) {
// A cache clean opearation is looking for a dirty block. Mark
// the packet so that the destination xbar can determine that
// there will be a follow-up write packet as well.
pkt->setSatisfied();
}
if (!memSidePort->sendTimingReq(pkt)) {
// we are awaiting a retry, but we
// delete the packet and will be creating a new packet
// when we get the opportunity
delete pkt;
// note that we have now masked any requestBus and
// schedSendEvent (we will wait for a retry before
// doing anything), and this is so even if we do not
// care about this packet and might override it before
// it gets retried
return true;
} else {
// As part of the call to sendTimingReq the packet is
// forwarded to all neighbouring caches (and any caches
// above them) as a snoop. Thus at this point we know if
// any of the neighbouring caches are responding, and if
// so, we know it is dirty, and we can determine if it is
// being passed as Modified, making our MSHR the ordering
// point
bool pending_modified_resp = !pkt->hasSharers() &&
pkt->cacheResponding();
markInService(mshr, pending_modified_resp);
if (pkt->isClean() && blk && blk->isDirty()) {
// A cache clean opearation is looking for a dirty
// block. If a dirty block is encountered a WriteClean
// will update any copies to the path to the memory
// until the point of reference.
DPRINTF(CacheVerbose, "%s: packet %s found block: %s\n",
__func__, pkt->print(), blk->print());
PacketPtr wb_pkt = writecleanBlk(blk, pkt->req->getDest(),
pkt->id);
PacketList writebacks;
writebacks.push_back(wb_pkt);
doWritebacks(writebacks, 0);
}
return false;
}
}
bool
Cache::sendWriteQueuePacket(WriteQueueEntry* wq_entry)
{
assert(wq_entry);
// always a single target for write queue entries
PacketPtr tgt_pkt = wq_entry->getTarget()->pkt;
DPRINTF(Cache, "%s: write %s\n", __func__, tgt_pkt->print());
// forward as is, both for evictions and uncacheable writes
if (!memSidePort->sendTimingReq(tgt_pkt)) {
// note that we have now masked any requestBus and
// schedSendEvent (we will wait for a retry before
// doing anything), and this is so even if we do not
// care about this packet and might override it before
// it gets retried
return true;
} else {
markInService(wq_entry);
return false;
}
}
void
Cache::serialize(CheckpointOut &cp) const
{
bool dirty(isDirty());
if (dirty) {
warn("*** The cache still contains dirty data. ***\n");
warn(" Make sure to drain the system using the correct flags.\n");
warn(" This checkpoint will not restore correctly and dirty data "
" in the cache will be lost!\n");
}
// Since we don't checkpoint the data in the cache, any dirty data
// will be lost when restoring from a checkpoint of a system that
// wasn't drained properly. Flag the checkpoint as invalid if the
// cache contains dirty data.
bool bad_checkpoint(dirty);
SERIALIZE_SCALAR(bad_checkpoint);
}
void
Cache::unserialize(CheckpointIn &cp)
{
bool bad_checkpoint;
UNSERIALIZE_SCALAR(bad_checkpoint);
if (bad_checkpoint) {
fatal("Restoring from checkpoints with dirty caches is not supported "
"in the classic memory system. Please remove any caches or "
" drain them properly before taking checkpoints.\n");
}
}
///////////////
//
// CpuSidePort
//
///////////////
AddrRangeList
Cache::CpuSidePort::getAddrRanges() const
{
return cache->getAddrRanges();
}
bool
Cache::CpuSidePort::tryTiming(PacketPtr pkt)
{
assert(!cache->system->bypassCaches());
// always let express snoop packets through if even if blocked
if (pkt->isExpressSnoop()) {
return true;
} else if (isBlocked() || mustSendRetry) {
// either already committed to send a retry, or blocked
mustSendRetry = true;
return false;
}
mustSendRetry = false;
return true;
}
bool
Cache::CpuSidePort::recvTimingReq(PacketPtr pkt)
{
assert(!cache->system->bypassCaches());
// always let express snoop packets through if even if blocked
if (pkt->isExpressSnoop()) {
bool M5_VAR_USED bypass_success = cache->recvTimingReq(pkt);
assert(bypass_success);
return true;
}
return tryTiming(pkt) && cache->recvTimingReq(pkt);
}
Tick
Cache::CpuSidePort::recvAtomic(PacketPtr pkt)
{
return cache->recvAtomic(pkt);
}
void
Cache::CpuSidePort::recvFunctional(PacketPtr pkt)
{
// functional request
cache->functionalAccess(pkt, true);
}
Cache::
CpuSidePort::CpuSidePort(const std::string &_name, Cache *_cache,
const std::string &_label)
: BaseCache::CacheSlavePort(_name, _cache, _label), cache(_cache)
{
}
Cache*
CacheParams::create()
{
assert(tags);
return new Cache(this);
}
///////////////
//
// MemSidePort
//
///////////////
bool
Cache::MemSidePort::recvTimingResp(PacketPtr pkt)
{
cache->recvTimingResp(pkt);
return true;
}
// Express snooping requests to memside port
void
Cache::MemSidePort::recvTimingSnoopReq(PacketPtr pkt)
{
// handle snooping requests
cache->recvTimingSnoopReq(pkt);
}
Tick
Cache::MemSidePort::recvAtomicSnoop(PacketPtr pkt)
{
return cache->recvAtomicSnoop(pkt);
}
void
Cache::MemSidePort::recvFunctionalSnoop(PacketPtr pkt)
{
// functional snoop (note that in contrast to atomic we don't have
// a specific functionalSnoop method, as they have the same
// behaviour regardless)
cache->functionalAccess(pkt, false);
}
void
Cache::CacheReqPacketQueue::sendDeferredPacket()
{
// sanity check
assert(!waitingOnRetry);
// there should never be any deferred request packets in the
// queue, instead we resly on the cache to provide the packets
// from the MSHR queue or write queue
assert(deferredPacketReadyTime() == MaxTick);
// check for request packets (requests & writebacks)
QueueEntry* entry = cache.getNextQueueEntry();
if (!entry) {
// can happen if e.g. we attempt a writeback and fail, but
// before the retry, the writeback is eliminated because
// we snoop another cache's ReadEx.
} else {
// let our snoop responses go first if there are responses to
// the same addresses
if (checkConflictingSnoop(entry->blkAddr)) {
return;
}
waitingOnRetry = entry->sendPacket(cache);
}
// if we succeeded and are not waiting for a retry, schedule the
// next send considering when the next queue is ready, note that
// snoop responses have their own packet queue and thus schedule
// their own events
if (!waitingOnRetry) {
schedSendEvent(cache.nextQueueReadyTime());
}
}
Cache::
MemSidePort::MemSidePort(const std::string &_name, Cache *_cache,
const std::string &_label)
: BaseCache::CacheMasterPort(_name, _cache, _reqQueue, _snoopRespQueue),
_reqQueue(*_cache, *this, _snoopRespQueue, _label),
_snoopRespQueue(*_cache, *this, _label), cache(_cache)
{
}