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/*
* Copyright (c) 2012-2013, 2018-2019 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
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*
* Copyright (c) 2003-2005 The Regents of The University of Michigan
* All rights reserved.
*
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* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
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/**
* @file
* Definition of BaseCache functions.
*/
#include "mem/cache/base.hh"
#include "base/compiler.hh"
#include "base/logging.hh"
#include "debug/Cache.hh"
#include "debug/CacheComp.hh"
#include "debug/CachePort.hh"
#include "debug/CacheRepl.hh"
#include "debug/CacheVerbose.hh"
#include "debug/HWPrefetch.hh"
#include "mem/cache/compressors/base.hh"
#include "mem/cache/mshr.hh"
#include "mem/cache/prefetch/base.hh"
#include "mem/cache/queue_entry.hh"
#include "mem/cache/tags/compressed_tags.hh"
#include "mem/cache/tags/super_blk.hh"
#include "params/BaseCache.hh"
#include "params/WriteAllocator.hh"
#include "sim/cur_tick.hh"
namespace gem5
{
BaseCache::CacheResponsePort::CacheResponsePort(const std::string &_name,
BaseCache *_cache,
const std::string &_label)
: QueuedResponsePort(_name, _cache, queue),
queue(*_cache, *this, true, _label),
blocked(false), mustSendRetry(false),
sendRetryEvent([this]{ processSendRetry(); }, _name)
{
}
BaseCache::BaseCache(const BaseCacheParams &p, unsigned blk_size)
: ClockedObject(p),
cpuSidePort (p.name + ".cpu_side_port", this, "CpuSidePort"),
memSidePort(p.name + ".mem_side_port", this, "MemSidePort"),
mshrQueue("MSHRs", p.mshrs, 0, p.demand_mshr_reserve, p.name),
writeBuffer("write buffer", p.write_buffers, p.mshrs, p.name),
tags(p.tags),
compressor(p.compressor),
prefetcher(p.prefetcher),
writeAllocator(p.write_allocator),
writebackClean(p.writeback_clean),
tempBlockWriteback(nullptr),
writebackTempBlockAtomicEvent([this]{ writebackTempBlockAtomic(); },
name(), false,
EventBase::Delayed_Writeback_Pri),
blkSize(blk_size),
lookupLatency(p.tag_latency),
dataLatency(p.data_latency),
forwardLatency(p.tag_latency),
fillLatency(p.data_latency),
responseLatency(p.response_latency),
sequentialAccess(p.sequential_access),
numTarget(p.tgts_per_mshr),
forwardSnoops(true),
clusivity(p.clusivity),
isReadOnly(p.is_read_only),
replaceExpansions(p.replace_expansions),
moveContractions(p.move_contractions),
blocked(0),
order(0),
noTargetMSHR(nullptr),
missCount(p.max_miss_count),
addrRanges(p.addr_ranges.begin(), p.addr_ranges.end()),
system(p.system),
stats(*this)
{
// the MSHR queue has no reserve entries as we check the MSHR
// queue on every single allocation, whereas the write queue has
// as many reserve entries as we have MSHRs, since every MSHR may
// eventually require a writeback, and we do not check the write
// buffer before committing to an MSHR
// forward snoops is overridden in init() once we can query
// whether the connected requestor is actually snooping or not
tempBlock = new TempCacheBlk(blkSize);
tags->tagsInit();
if (prefetcher)
prefetcher->setCache(this);
fatal_if(compressor && !dynamic_cast<CompressedTags*>(tags),
"The tags of compressed cache %s must derive from CompressedTags",
name());
warn_if(!compressor && dynamic_cast<CompressedTags*>(tags),
"Compressed cache %s does not have a compression algorithm", name());
if (compressor)
compressor->setCache(this);
}
BaseCache::~BaseCache()
{
delete tempBlock;
}
void
BaseCache::CacheResponsePort::setBlocked()
{
assert(!blocked);
DPRINTF(CachePort, "Port is blocking new requests\n");
blocked = true;
// if we already scheduled a retry in this cycle, but it has not yet
// happened, cancel it
if (sendRetryEvent.scheduled()) {
owner.deschedule(sendRetryEvent);
DPRINTF(CachePort, "Port descheduled retry\n");
mustSendRetry = true;
}
}
void
BaseCache::CacheResponsePort::clearBlocked()
{
assert(blocked);
DPRINTF(CachePort, "Port is accepting new requests\n");
blocked = false;
if (mustSendRetry) {
// @TODO: need to find a better time (next cycle?)
owner.schedule(sendRetryEvent, curTick() + 1);
}
}
void
BaseCache::CacheResponsePort::processSendRetry()
{
DPRINTF(CachePort, "Port is sending retry\n");
// reset the flag and call retry
mustSendRetry = false;
sendRetryReq();
}
Addr
BaseCache::regenerateBlkAddr(CacheBlk* blk)
{
if (blk != tempBlock) {
return tags->regenerateBlkAddr(blk);
} else {
return tempBlock->getAddr();
}
}
void
BaseCache::init()
{
if (!cpuSidePort.isConnected() || !memSidePort.isConnected())
fatal("Cache ports on %s are not connected\n", name());
cpuSidePort.sendRangeChange();
forwardSnoops = cpuSidePort.isSnooping();
}
Port &
BaseCache::getPort(const std::string &if_name, PortID idx)
{
if (if_name == "mem_side") {
return memSidePort;
} else if (if_name == "cpu_side") {
return cpuSidePort;
} else {
return ClockedObject::getPort(if_name, idx);
}
}
bool
BaseCache::inRange(Addr addr) const
{
for (const auto& r : addrRanges) {
if (r.contains(addr)) {
return true;
}
}
return false;
}
void
BaseCache::handleTimingReqHit(PacketPtr pkt, CacheBlk *blk, Tick request_time)
{
// handle special cases for LockedRMW transactions
if (pkt->isLockedRMW()) {
Addr blk_addr = pkt->getBlockAddr(blkSize);
if (pkt->isRead()) {
// Read hit for LockedRMW. Since it requires exclusive
// permissions, there should be no outstanding access.
assert(!mshrQueue.findMatch(blk_addr, pkt->isSecure()));
// The keys to LockedRMW are that (1) we always have an MSHR
// allocated during the RMW interval to catch snoops and
// defer them until after the RMW completes, and (2) we
// clear permissions on the block to turn any upstream
// access other than the matching write into a miss, causing
// it to append to the MSHR as well.
// Because we hit in the cache, we have to fake an MSHR to
// achieve part (1). If the read had missed, this MSHR
// would get allocated as part of normal miss processing.
// Basically we need to get the MSHR in the same state as if
// we had missed and just received the response.
// Request *req2 = new Request(*(pkt->req));
RequestPtr req2 = std::make_shared<Request>(*(pkt->req));
PacketPtr pkt2 = new Packet(req2, pkt->cmd);
MSHR *mshr = allocateMissBuffer(pkt2, curTick(), true);
// Mark the MSHR "in service" (even though it's not) to prevent
// the cache from sending out a request.
mshrQueue.markInService(mshr, false);
// Part (2): mark block inaccessible
assert(blk);
blk->clearCoherenceBits(CacheBlk::ReadableBit);
blk->clearCoherenceBits(CacheBlk::WritableBit);
} else {
assert(pkt->isWrite());
// All LockedRMW writes come here, as they cannot miss.
// Need to undo the two things described above. Block
// permissions were already restored earlier in this
// function, prior to the access() call. Now we just need
// to clear out the MSHR.
// Read should have already allocated MSHR.
MSHR *mshr = mshrQueue.findMatch(blk_addr, pkt->isSecure());
assert(mshr);
// Fake up a packet and "respond" to the still-pending
// LockedRMWRead, to process any pending targets and clear
// out the MSHR
PacketPtr resp_pkt =
new Packet(pkt->req, MemCmd::LockedRMWWriteResp);
resp_pkt->senderState = mshr;
recvTimingResp(resp_pkt);
}
}
if (pkt->needsResponse()) {
// These delays should have been consumed by now
assert(pkt->headerDelay == 0);
assert(pkt->payloadDelay == 0);
pkt->makeTimingResponse();
// 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 the value of lat overriden by access(), which calls
// the calculateAccessLatency() function.
cpuSidePort.schedTimingResp(pkt, request_time);
} 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);
}
}
void
BaseCache::handleTimingReqMiss(PacketPtr pkt, MSHR *mshr, CacheBlk *blk,
Tick forward_time, Tick request_time)
{
if (writeAllocator &&
pkt && pkt->isWrite() && !pkt->req->isUncacheable()) {
writeAllocator->updateMode(pkt->getAddr(), pkt->getSize(),
pkt->getBlockAddr(blkSize));
}
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->requestorId() < system->maxRequestors());
stats.cmdStats(pkt).mshrHits[pkt->req->requestorId()]++;
// 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);
}
}
}
} else {
// no MSHR
assert(pkt->req->requestorId() < system->maxRequestors());
stats.cmdStats(pkt).mshrMisses[pkt->req->requestorId()]++;
if (prefetcher && pkt->isDemand())
prefetcher->incrDemandMhsrMisses();
if (pkt->isEviction() || pkt->cmd == MemCmd::WriteClean) {
// We use forward_time here because there is an
// writeback or writeclean, forwarded to WriteBuffer.
allocateWriteBuffer(pkt, forward_time);
} else {
if (blk && blk->isValid()) {
// 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->isSet(CacheBlk::WritableBit)) ||
pkt->req->isCacheMaintenance());
blk->clearCoherenceBits(CacheBlk::ReadableBit);
}
// Here we are using forward_time, modelling the latency of
// a miss (outbound) just as forwardLatency, neglecting the
// lookupLatency component.
allocateMissBuffer(pkt, forward_time);
}
}
}
void
BaseCache::recvTimingReq(PacketPtr pkt)
{
// anything that is merely forwarded pays for the forward latency and
// the delay provided by the crossbar
Tick forward_time = clockEdge(forwardLatency) + pkt->headerDelay;
if (pkt->cmd == MemCmd::LockedRMWWriteReq) {
// For LockedRMW accesses, we mark the block inaccessible after the
// read (see below), to make sure no one gets in before the write.
// Now that the write is here, mark it accessible again, so the
// write will succeed. LockedRMWReadReq brings the block in in
// exclusive mode, so we know it was previously writable.
CacheBlk *blk = tags->findBlock(pkt->getAddr(), pkt->isSecure());
assert(blk && blk->isValid());
assert(!blk->isSet(CacheBlk::WritableBit) &&
!blk->isSet(CacheBlk::ReadableBit));
blk->setCoherenceBits(CacheBlk::ReadableBit);
blk->setCoherenceBits(CacheBlk::WritableBit);
}
Cycles lat;
CacheBlk *blk = nullptr;
bool satisfied = false;
{
PacketList writebacks;
// Note that lat is passed by reference here. The function
// access() will set the lat value.
satisfied = access(pkt, blk, lat, writebacks);
// After the evicted blocks are selected, they must be forwarded
// to the write buffer to ensure they logically precede anything
// happening below
doWritebacks(writebacks, clockEdge(lat + forwardLatency));
}
// Here we charge the headerDelay that takes into account the latencies
// of the bus, if the packet comes from it.
// The latency charged is just the value set by the access() function.
// 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);
// Here we reset the timing of the packet.
pkt->headerDelay = pkt->payloadDelay = 0;
if (satisfied) {
// notify before anything else as later handleTimingReqHit might turn
// the packet in a response
ppHit->notify(pkt);
if (prefetcher && blk && blk->wasPrefetched()) {
DPRINTF(Cache, "Hit on prefetch for addr %#x (%s)\n",
pkt->getAddr(), pkt->isSecure() ? "s" : "ns");
blk->clearPrefetched();
}
handleTimingReqHit(pkt, blk, request_time);
} else {
handleTimingReqMiss(pkt, blk, forward_time, request_time);
ppMiss->notify(pkt);
}
if (prefetcher) {
// track time of availability of next prefetch, if any
Tick next_pf_time = prefetcher->nextPrefetchReadyTime();
if (next_pf_time != MaxTick) {
schedMemSideSendEvent(next_pf_time);
}
}
}
void
BaseCache::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);
}
void
BaseCache::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());
const 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() && pkt->cmd != MemCmd::LockedRMWWriteResp) {
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
const QueueEntry::Target *initial_tgt = mshr->getTarget();
const Tick miss_latency = curTick() - initial_tgt->recvTime;
if (pkt->req->isUncacheable()) {
assert(pkt->req->requestorId() < system->maxRequestors());
stats.cmdStats(initial_tgt->pkt)
.mshrUncacheableLatency[pkt->req->requestorId()] += miss_latency;
} else {
assert(pkt->req->requestorId() < system->maxRequestors());
stats.cmdStats(initial_tgt->pkt)
.mshrMissLatency[pkt->req->requestorId()] += miss_latency;
}
PacketList writebacks;
bool is_fill = !mshr->isForward &&
(pkt->isRead() || pkt->cmd == MemCmd::UpgradeResp ||
mshr->wasWholeLineWrite);
// make sure that if the mshr was due to a whole line write then
// the response is an invalidation
assert(!mshr->wasWholeLineWrite || pkt->isInvalidate());
CacheBlk *blk = tags->findBlock(pkt->getAddr(), pkt->isSecure());
if (is_fill && !is_error) {
DPRINTF(Cache, "Block for addr %#llx being updated in Cache\n",
pkt->getAddr());
const bool allocate = (writeAllocator && mshr->wasWholeLineWrite) ?
writeAllocator->allocate() : mshr->allocOnFill();
blk = handleFill(pkt, blk, writebacks, allocate);
assert(blk != nullptr);
ppFill->notify(pkt);
}
// Don't want to promote the Locked RMW Read until
// the locked write comes in
if (!mshr->hasLockedRMWReadTarget()) {
if (blk && blk->isValid() && pkt->isClean() && !pkt->isInvalidate()) {
// The block was marked not readable while there was a pending
// cache maintenance operation, restore its flag.
blk->setCoherenceBits(CacheBlk::ReadableBit);
// This was a cache clean operation (without invalidate)
// and we have a copy of the block already. Since there
// is no invalidation, we can promote targets that don't
// require a writable copy
mshr->promoteReadable();
}
if (blk && blk->isSet(CacheBlk::WritableBit) &&
!pkt->req->isCacheInvalidate()) {
// If at this point the referenced block is writable and the
// response is not a cache invalidate, we promote targets that
// were deferred as we couldn't guarrantee a writable copy
mshr->promoteWritable();
}
}
serviceMSHRTargets(mshr, pkt, blk);
// We are stopping servicing targets early for the Locked RMW Read until
// the write comes.
if (!mshr->hasLockedRMWReadTarget()) {
if (mshr->promoteDeferredTargets()) {
// avoid later read getting stale data while write miss is
// outstanding.. see comment in timingAccess()
if (blk) {
blk->clearCoherenceBits(CacheBlk::ReadableBit);
}
mshrQueue.markPending(mshr);
schedMemSideSendEvent(clockEdge() + pkt->payloadDelay);
} else {
// while we deallocate an mshr from the queue we still have to
// check the isFull condition before and after as we might
// have been using the reserved entries already
const bool was_full = mshrQueue.isFull();
mshrQueue.deallocate(mshr);
if (was_full && !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() && !isBlocked()) {
Tick next_pf_time = std::max(
prefetcher->nextPrefetchReadyTime(), clockEdge());
if (next_pf_time != MaxTick)
schedMemSideSendEvent(next_pf_time);
}
}
// if we used temp block, check to see if its valid and then clear it
if (blk == tempBlock && tempBlock->isValid()) {
evictBlock(blk, writebacks);
}
}
const Tick forward_time = clockEdge(forwardLatency) + pkt->headerDelay;
// copy writebacks to write buffer
doWritebacks(writebacks, forward_time);
DPRINTF(CacheVerbose, "%s: Leaving with %s\n", __func__, pkt->print());
delete pkt;
}
Tick
BaseCache::recvAtomic(PacketPtr pkt)
{
// should assert here that there are no outstanding MSHRs or
// writebacks... that would mean that someone used an atomic
// access in timing mode
// We use lookupLatency here because it is used to specify the latency
// to access.
Cycles lat = lookupLatency;
CacheBlk *blk = nullptr;
PacketList writebacks;
bool satisfied = access(pkt, blk, lat, writebacks);
if (pkt->isClean() && blk && blk->isSet(CacheBlk::DirtyBit)) {
// 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 precede anything happening below
doWritebacksAtomic(writebacks);
assert(writebacks.empty());
if (!satisfied) {
lat += handleAtomicReqMiss(pkt, blk, writebacks);
}
// 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 = evictBlock(blk);
}
if (pkt->needsResponse()) {
pkt->makeAtomicResponse();
}
return lat * clockPeriod();
}
void
BaseCache::functionalAccess(PacketPtr pkt, bool from_cpu_side)
{
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->trySatisfyFunctional(&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->isSet(CacheBlk::DirtyBit) ||
(mshr && mshr->inService && mshr->isPendingModified()));
bool done = have_dirty ||
cpuSidePort.trySatisfyFunctional(pkt) ||
mshrQueue.trySatisfyFunctional(pkt) ||
writeBuffer.trySatisfyFunctional(pkt) ||
memSidePort.trySatisfyFunctional(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 (from_cpu_side) {
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);
}
}
}
void
BaseCache::updateBlockData(CacheBlk *blk, const PacketPtr cpkt,
bool has_old_data)
{
DataUpdate data_update(regenerateBlkAddr(blk), blk->isSecure());
if (ppDataUpdate->hasListeners()) {
if (has_old_data) {
data_update.oldData = std::vector<uint64_t>(blk->data,
blk->data + (blkSize / sizeof(uint64_t)));
}
}
// Actually perform the data update
if (cpkt) {
cpkt->writeDataToBlock(blk->data, blkSize);
}
if (ppDataUpdate->hasListeners()) {
if (cpkt) {
data_update.newData = std::vector<uint64_t>(blk->data,
blk->data + (blkSize / sizeof(uint64_t)));
}
ppDataUpdate->notify(data_update);
}
}
void
BaseCache::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 = pkt->getOffset(blkSize);
uint8_t *blk_data = blk->data + offset;
assert(sizeof(uint64_t) >= pkt->getSize());
// Get a copy of the old block's contents for the probe before the update
DataUpdate data_update(regenerateBlkAddr(blk), blk->isSecure());
if (ppDataUpdate->hasListeners()) {
data_update.oldData = std::vector<uint64_t>(blk->data,
blk->data + (blkSize / sizeof(uint64_t)));
}
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->setCoherenceBits(CacheBlk::DirtyBit);
if (ppDataUpdate->hasListeners()) {
data_update.newData = std::vector<uint64_t>(blk->data,
blk->data + (blkSize / sizeof(uint64_t)));
ppDataUpdate->notify(data_update);
}
}
}
QueueEntry*
BaseCache::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);
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);
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() && !isBlocked()) {
// 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())) {
DPRINTF(HWPrefetch, "Prefetch %#x has hit in cache, "
"dropped.\n", pf_addr);
prefetcher->pfHitInCache();
// free the request and packet
delete pkt;
} else if (mshrQueue.findMatch(pf_addr, pkt->isSecure())) {
DPRINTF(HWPrefetch, "Prefetch %#x has hit in a MSHR, "
"dropped.\n", pf_addr);
prefetcher->pfHitInMSHR();
// free the request and packet
delete pkt;
} else if (writeBuffer.findMatch(pf_addr, pkt->isSecure())) {
DPRINTF(HWPrefetch, "Prefetch %#x has hit in the "
"Write Buffer, dropped.\n", pf_addr);
prefetcher->pfHitInWB();
// free the request and packet
delete pkt;
} else {
// Update statistic on number of prefetches issued
// (hwpf_mshr_misses)
assert(pkt->req->requestorId() < system->maxRequestors());
stats.cmdStats(pkt).mshrMisses[pkt->req->requestorId()]++;
// 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);
}
}
}
return nullptr;
}
bool
BaseCache::handleEvictions(std::vector<CacheBlk*> &evict_blks,
PacketList &writebacks)
{
bool replacement = false;
for (const auto& blk : evict_blks) {
if (blk->isValid()) {
replacement = true;
const MSHR* mshr =
mshrQueue.findMatch(regenerateBlkAddr(blk), blk->isSecure());
if (mshr) {
// Must be an outstanding upgrade or clean request on a block
// we're about to replace
assert((!blk->isSet(CacheBlk::WritableBit) &&
mshr->needsWritable()) || mshr->isCleaning());
return false;
}
}
}
// The victim will be replaced by a new entry, so increase the replacement
// counter if a valid block is being replaced
if (replacement) {
stats.replacements++;
// Evict valid blocks associated to this victim block
for (auto& blk : evict_blks) {
if (blk->isValid()) {
evictBlock(blk, writebacks);
}
}
}
return true;
}
bool
BaseCache::updateCompressionData(CacheBlk *&blk, const uint64_t* data,
PacketList &writebacks)
{
// tempBlock does not exist in the tags, so don't do anything for it.
if (blk == tempBlock) {
return true;
}
// The compressor is called to compress the updated data, so that its
// metadata can be updated.
Cycles compression_lat = Cycles(0);
Cycles decompression_lat = Cycles(0);
const auto comp_data =
compressor->compress(data, compression_lat, decompression_lat);
std::size_t compression_size = comp_data->getSizeBits();
// Get previous compressed size
CompressionBlk* compression_blk = static_cast<CompressionBlk*>(blk);
[[maybe_unused]] const std::size_t prev_size =
compression_blk->getSizeBits();
// If compressed size didn't change enough to modify its co-allocatability
// there is nothing to do. Otherwise we may be facing a data expansion
// (block passing from more compressed to less compressed state), or a
// data contraction (less to more).
bool is_data_expansion = false;
bool is_data_contraction = false;
const CompressionBlk::OverwriteType overwrite_type =
compression_blk->checkExpansionContraction(compression_size);
std::string op_name = "";
if (overwrite_type == CompressionBlk::DATA_EXPANSION) {
op_name = "expansion";
is_data_expansion = true;
} else if ((overwrite_type == CompressionBlk::DATA_CONTRACTION) &&
moveContractions) {
op_name = "contraction";
is_data_contraction = true;
}
// If block changed compression state, it was possibly co-allocated with
// other blocks and cannot be co-allocated anymore, so one or more blocks
// must be evicted to make room for the expanded/contracted block
std::vector<CacheBlk*> evict_blks;
if (is_data_expansion || is_data_contraction) {
std::vector<CacheBlk*> evict_blks;
bool victim_itself = false;
CacheBlk *victim = nullptr;
if (replaceExpansions || is_data_contraction) {
victim = tags->findVictim(regenerateBlkAddr(blk),
blk->isSecure(), compression_size, evict_blks);
// It is valid to return nullptr if there is no victim
if (!victim) {
return false;
}
// If the victim block is itself the block won't need to be moved,
// and the victim should not be evicted
if (blk == victim) {
victim_itself = true;
auto it = std::find_if(evict_blks.begin(), evict_blks.end(),
[&blk](CacheBlk* evict_blk){ return evict_blk == blk; });
evict_blks.erase(it);
}
// Print victim block's information
DPRINTF(CacheRepl, "Data %s replacement victim: %s\n",
op_name, victim->print());
} else {
// If we do not move the expanded block, we must make room for
// the expansion to happen, so evict every co-allocated block
const SuperBlk* superblock = static_cast<const SuperBlk*>(
compression_blk->getSectorBlock());
for (auto& sub_blk : superblock->blks) {
if (sub_blk->isValid() && (blk != sub_blk)) {
evict_blks.push_back(sub_blk);
}
}
}
// Try to evict blocks; if it fails, give up on update
if (!handleEvictions(evict_blks, writebacks)) {
return false;
}
DPRINTF(CacheComp, "Data %s: [%s] from %d to %d bits\n",
op_name, blk->print(), prev_size, compression_size);
if (!victim_itself && (replaceExpansions || is_data_contraction)) {
// Move the block's contents to the invalid block so that it now
// co-allocates with the other existing superblock entry
tags->moveBlock(blk, victim);
blk = victim;
compression_blk = static_cast<CompressionBlk*>(blk);
}
}
// Update the number of data expansions/contractions
if (is_data_expansion) {
stats.dataExpansions++;
} else if (is_data_contraction) {
stats.dataContractions++;
}
compression_blk->setSizeBits(compression_size);
compression_blk->setDecompressionLatency(decompression_lat);
return true;
}
void
BaseCache::satisfyRequest(PacketPtr pkt, CacheBlk *blk, bool, bool)
{
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 requestor(s) to have buffered the ReadEx snoop and to
// invalidate their blocks after receiving them.
// assert(!pkt->needsWritable() || blk->isSet(CacheBlk::WritableBit));
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) {
if (pkt->isAtomicOp()) {
// Get a copy of the old block's contents for the probe before
// the update
DataUpdate data_update(regenerateBlkAddr(blk), blk->isSecure());
if (ppDataUpdate->hasListeners()) {
data_update.oldData = std::vector<uint64_t>(blk->data,
blk->data + (blkSize / sizeof(uint64_t)));
}
// extract data from cache and save it into the data field in
// the packet as a return value from this atomic op
int offset = tags->extractBlkOffset(pkt->getAddr());
uint8_t *blk_data = blk->data + offset;
pkt->setData(blk_data);
// execute AMO operation
(*(pkt->getAtomicOp()))(blk_data);
// Inform of this block's data contents update
if (ppDataUpdate->hasListeners()) {
data_update.newData = std::vector<uint64_t>(blk->data,
blk->data + (blkSize / sizeof(uint64_t)));
ppDataUpdate->notify(data_update);
}
// set block status to dirty
blk->setCoherenceBits(CacheBlk::DirtyBit);
} else {
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->isSet(CacheBlk::WritableBit));
// Write or WriteLine at the first cache with block in writable state
if (blk->checkWrite(pkt)) {
updateBlockData(blk, pkt, true);
}
// 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->setCoherenceBits(CacheBlk::DirtyBit);
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);
} else if (pkt->isUpgrade()) {
// sanity check
assert(!pkt->hasSharers());
if (blk->isSet(CacheBlk::DirtyBit)) {
// 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->clearCoherenceBits(CacheBlk::DirtyBit);
}
} else if (pkt->isClean()) {
blk->clearCoherenceBits(CacheBlk::DirtyBit);
} 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
//
/////////////////////////////////////////////////////
Cycles
BaseCache::calculateTagOnlyLatency(const uint32_t delay,
const Cycles lookup_lat) const
{
// A tag-only access has to wait for the packet to arrive in order to
// perform the tag lookup.
return ticksToCycles(delay) + lookup_lat;
}
Cycles
BaseCache::calculateAccessLatency(const CacheBlk* blk, const uint32_t delay,
const Cycles lookup_lat) const
{
Cycles lat(0);
if (blk != nullptr) {
// As soon as the access arrives, for sequential accesses first access
// tags, then the data entry. In the case of parallel accesses the
// latency is dictated by the slowest of tag and data latencies.
if (sequentialAccess) {
lat = ticksToCycles(delay) + lookup_lat + dataLatency;
} else {
lat = ticksToCycles(delay) + std::max(lookup_lat, dataLatency);
}
// Check if the block to be accessed is available. If not, apply the
// access latency on top of when the block is ready to be accessed.
const Tick tick = curTick() + delay;
const Tick when_ready = blk->getWhenReady();
if (when_ready > tick &&
ticksToCycles(when_ready - tick) > lat) {
lat += ticksToCycles(when_ready - tick);
}
} else {
// In case of a miss, we neglect the data access in a parallel
// configuration (i.e., the data access will be stopped as soon as
// we find out it is a miss), and use the tag-only latency.
lat = calculateTagOnlyLatency(delay, lookup_lat);
}
return lat;
}
bool
BaseCache::access(PacketPtr pkt, CacheBlk *&blk, Cycles &lat,
PacketList &writebacks)
{
// sanity check
assert(pkt->isRequest());
gem5_assert(!(isReadOnly && pkt->isWrite()),
"Should never see a write in a read-only cache %s\n",
name());
// Access block in the tags
Cycles tag_latency(0);
blk = tags->accessBlock(pkt, tag_latency);
DPRINTF(Cache, "%s for %s %s\n", __func__, 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.
// Calculate access latency on top of when the packet arrives. This
// takes into account the bus delay.
lat = calculateTagOnlyLatency(pkt->headerDelay, tag_latency);
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();
// A clean evict does not need to access the data array
lat = calculateTagOnlyLatency(pkt->headerDelay, tag_latency);
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;
}
}
}
// The critical latency part of a write depends only on the tag access
if (pkt->isWrite()) {
lat = calculateTagOnlyLatency(pkt->headerDelay, tag_latency);
}
// 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());
// A writeback searches for the block, then writes the data.
// As the writeback is being dropped, the data is not touched,
// and we just had to wait for the time to find a match in the
// MSHR. As of now assume a mshr queue search takes as long as
// a tag lookup for simplicity.
return true;
}
const bool has_old_data = blk && blk->isValid();
if (!blk) {
// need to do a replacement
blk = allocateBlock(pkt, writebacks);
if (!blk) {
// no replaceable block available: give up, fwd to next level.
incMissCount(pkt);
return false;
}
blk->setCoherenceBits(CacheBlk::ReadableBit);
} else if (compressor) {
// This is an overwrite to an existing block, therefore we need
// to check for data expansion (i.e., block was compressed with
// a smaller size, and now it doesn't fit the entry anymore).
// If that is the case we might need to evict blocks.
if (!updateCompressionData(blk, pkt->getConstPtr<uint64_t>(),
writebacks)) {
invalidateBlock(blk);
return false;
}
}
// 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) {
// TODO: the coherent cache can assert that the dirty bit is set
blk->setCoherenceBits(CacheBlk::DirtyBit);
}
// 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->setCoherenceBits(CacheBlk::WritableBit);
}
// nothing else to do; writeback doesn't expect response
assert(!pkt->needsResponse());
updateBlockData(blk, pkt, has_old_data);
DPRINTF(Cache, "%s new state is %s\n", __func__, blk->print());
incHitCount(pkt);
// When the packet metadata arrives, the tag lookup will be done while
// the payload is arriving. Then the block will be ready to access as
// soon as the fill is done
blk->setWhenReady(clockEdge(fillLatency) + pkt->headerDelay +
std::max(cyclesToTicks(tag_latency), (uint64_t)pkt->payloadDelay));
return true;
} else if (pkt->cmd == MemCmd::CleanEvict) {
// A CleanEvict does not need to access the data array
lat = calculateTagOnlyLatency(pkt->headerDelay, tag_latency);
if (blk) {
// 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());
const bool has_old_data = blk && blk->isValid();
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, writebacks);
if (!blk) {
// no replaceable block available: give up, fwd to
// next level.
incMissCount(pkt);
return false;
}
blk->setCoherenceBits(CacheBlk::ReadableBit);
}
} else if (compressor) {
// This is an overwrite to an existing block, therefore we need
// to check for data expansion (i.e., block was compressed with
// a smaller size, and now it doesn't fit the entry anymore).
// If that is the case we might need to evict blocks.
if (!updateCompressionData(blk, pkt->getConstPtr<uint64_t>(),
writebacks)) {
invalidateBlock(blk);
return false;
}
}
// 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);
// TODO: the coherent cache can assert that the dirty bit is set
if (!pkt->writeThrough()) {
blk->setCoherenceBits(CacheBlk::DirtyBit);
}
// nothing else to do; writeback doesn't expect response
assert(!pkt->needsResponse());
updateBlockData(blk, pkt, has_old_data);
DPRINTF(Cache, "%s new state is %s\n", __func__, blk->print());
incHitCount(pkt);
// When the packet metadata arrives, the tag lookup will be done while
// the payload is arriving. Then the block will be ready to access as
// soon as the fill is done
blk->setWhenReady(clockEdge(fillLatency) + pkt->headerDelay +
std::max(cyclesToTicks(tag_latency), (uint64_t)pkt->payloadDelay));
// If this a write-through packet it will be sent to cache below
return !pkt->writeThrough();
} else if (blk && (pkt->needsWritable() ?
blk->isSet(CacheBlk::WritableBit) :
blk->isSet(CacheBlk::ReadableBit))) {
// OK to satisfy access
incHitCount(pkt);
// Calculate access latency based on the need to access the data array
if (pkt->isRead()) {
lat = calculateAccessLatency(blk, pkt->headerDelay, tag_latency);
// When a block is compressed, it must first be decompressed
// before being read. This adds to the access latency.
if (compressor) {
lat += compressor->getDecompressionLatency(blk);
}
} else {
lat = calculateTagOnlyLatency(pkt->headerDelay, tag_latency);
}
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);
lat = calculateAccessLatency(blk, pkt->headerDelay, tag_latency);
if (!blk && pkt->isLLSC() && pkt->isWrite()) {
// complete miss on store conditional... just give up now
pkt->req->setExtraData(0);
return true;
}
return false;
}
void
BaseCache::maintainClusivity(bool from_cache, CacheBlk *blk)
{
if (from_cache && blk && blk->isValid() &&
!blk->isSet(CacheBlk::DirtyBit) && 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);
}
}
CacheBlk*
BaseCache::handleFill(PacketPtr pkt, CacheBlk *blk, PacketList &writebacks,
bool allocate)
{
assert(pkt->isResponse());
Addr addr = pkt->getAddr();
bool is_secure = pkt->isSecure();
const bool has_old_data = blk && blk->isValid();
const std::string old_state = (debug::Cache && blk) ? blk->print() : "";
// 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) {
// better have read new data...
assert(pkt->hasData() || pkt->cmd == MemCmd::InvalidateResp);
// need to do a replacement if allocating, otherwise we stick
// with the temporary storage
blk = allocate ? allocateBlock(pkt, writebacks) : nullptr;
if (!blk) {
// No replaceable block or a mostly exclusive
// cache... just use temporary storage to complete the
// current request and then get rid of it
blk = tempBlock;
tempBlock->insert(addr, is_secure);
DPRINTF(Cache, "using temp block for %#llx (%s)\n", addr,
is_secure ? "s" : "ns");
}
} else {
// existing block... probably an upgrade
// don't clear block status... if block is already dirty we
// don't want to lose that
}
// Block is guaranteed to be valid at this point
assert(blk->isValid());
assert(blk->isSecure() == is_secure);
assert(regenerateBlkAddr(blk) == addr);
blk->setCoherenceBits(CacheBlk::ReadableBit);
// 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::InvalidateResp) {
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->setCoherenceBits(CacheBlk::WritableBit);
// 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->setCoherenceBits(CacheBlk::DirtyBit);
gem5_assert(!isReadOnly, "Should never see dirty snoop response "
"in read-only cache %s\n", name());
}
}
DPRINTF(Cache, "Block addr %#llx (%s) moving from %s 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);
updateBlockData(blk, pkt, has_old_data);
}
// The block will be ready when the payload arrives and the fill is done
blk->setWhenReady(clockEdge(fillLatency) + pkt->headerDelay +
pkt->payloadDelay);
return blk;
}
CacheBlk*
BaseCache::allocateBlock(const PacketPtr pkt, PacketList &writebacks)
{
// Get address
const Addr addr = pkt->getAddr();
// Get secure bit
const bool is_secure = pkt->isSecure();
// Block size and compression related access latency. Only relevant if
// using a compressor, otherwise there is no extra delay, and the block
// is fully sized
std::size_t blk_size_bits = blkSize*8;
Cycles compression_lat = Cycles(0);
Cycles decompression_lat = Cycles(0);
// If a compressor is being used, it is called to compress data before
// insertion. Although in Gem5 the data is stored uncompressed, even if a
// compressor is used, the compression/decompression methods are called to
// calculate the amount of extra cycles needed to read or write compressed
// blocks.
if (compressor && pkt->hasData()) {
const auto comp_data = compressor->compress(
pkt->getConstPtr<uint64_t>(), compression_lat, decompression_lat);
blk_size_bits = comp_data->getSizeBits();
}
// Find replacement victim
std::vector<CacheBlk*> evict_blks;
CacheBlk *victim = tags->findVictim(addr, is_secure, blk_size_bits,
evict_blks);
// It is valid to return nullptr if there is no victim
if (!victim)
return nullptr;
// Print victim block's information
DPRINTF(CacheRepl, "Replacement victim: %s\n", victim->print());
// Try to evict blocks; if it fails, give up on allocation
if (!handleEvictions(evict_blks, writebacks)) {
return nullptr;
}
// Insert new block at victimized entry
tags->insertBlock(pkt, victim);
// If using a compressor, set compression data. This must be done after
// insertion, as the compression bit may be set.
if (compressor) {
compressor->setSizeBits(victim, blk_size_bits);
compressor->setDecompressionLatency(victim, decompression_lat);
}
return victim;
}
void
BaseCache::invalidateBlock(CacheBlk *blk)
{
// If block is still marked as prefetched, then it hasn't been used
if (blk->wasPrefetched()) {
prefetcher->prefetchUnused();
}
// Notify that the data contents for this address are no longer present
updateBlockData(blk, nullptr, blk->isValid());
// If handling a block present in the Tags, let it do its invalidation
// process, which will update stats and invalidate the block itself
if (blk != tempBlock) {
tags->invalidate(blk);
} else {
tempBlock->invalidate();
}
}
void
BaseCache::evictBlock(CacheBlk *blk, PacketList &writebacks)
{
PacketPtr pkt = evictBlock(blk);
if (pkt) {
writebacks.push_back(pkt);
}
}
PacketPtr
BaseCache::writebackBlk(CacheBlk *blk)
{
gem5_assert(!isReadOnly || writebackClean,
"Writeback from read-only cache");
assert(blk && blk->isValid() &&
(blk->isSet(CacheBlk::DirtyBit) || writebackClean));
stats.writebacks[Request::wbRequestorId]++;
RequestPtr req = std::make_shared<Request>(
regenerateBlkAddr(blk), blkSize, 0, Request::wbRequestorId);
if (blk->isSecure())
req->setFlags(Request::SECURE);
req->taskId(blk->getTaskId());
PacketPtr pkt =
new Packet(req, blk->isSet(CacheBlk::DirtyBit) ?
MemCmd::WritebackDirty : MemCmd::WritebackClean);
DPRINTF(Cache, "Create Writeback %s writable: %d, dirty: %d\n",
pkt->print(), blk->isSet(CacheBlk::WritableBit),
blk->isSet(CacheBlk::DirtyBit));
if (blk->isSet(CacheBlk::WritableBit)) {
// not asserting shared means we pass the block in modified
// state, mark our own block non-writeable
blk->clearCoherenceBits(CacheBlk::WritableBit);
} else {
// we are in the Owned state, tell the receiver
pkt->setHasSharers();
}
// make sure the block is not marked dirty
blk->clearCoherenceBits(CacheBlk::DirtyBit);
pkt->allocate();
pkt->setDataFromBlock(blk->data, blkSize);
// When a block is compressed, it must first be decompressed before being
// sent for writeback.
if (compressor) {
pkt->payloadDelay = compressor->getDecompressionLatency(blk);
}
return pkt;
}
PacketPtr
BaseCache::writecleanBlk(CacheBlk *blk, Request::Flags dest, PacketId id)
{
RequestPtr req = std::make_shared<Request>(
regenerateBlkAddr(blk), blkSize, 0, Request::wbRequestorId);
if (blk->isSecure()) {
req->setFlags(Request::SECURE);
}
req->taskId(blk->getTaskId());
PacketPtr pkt = new Packet(req, MemCmd::WriteClean, blkSize, id);
if (dest) {
req->setFlags(dest);
pkt->setWriteThrough();
}
DPRINTF(Cache, "Create %s writable: %d, dirty: %d\n", pkt->print(),
blk->isSet(CacheBlk::WritableBit), blk->isSet(CacheBlk::DirtyBit));
if (blk->isSet(CacheBlk::WritableBit)) {
// not asserting shared means we pass the block in modified
// state, mark our own block non-writeable
blk->clearCoherenceBits(CacheBlk::WritableBit);
} else {
// we are in the Owned state, tell the receiver
pkt->setHasSharers();
}
// make sure the block is not marked dirty
blk->clearCoherenceBits(CacheBlk::DirtyBit);
pkt->allocate();
pkt->setDataFromBlock(blk->data, blkSize);
// When a block is compressed, it must first be decompressed before being
// sent for writeback.
if (compressor) {
pkt->payloadDelay = compressor->getDecompressionLatency(blk);
}
return pkt;
}
void
BaseCache::memWriteback()
{
tags->forEachBlk([this](CacheBlk &blk) { writebackVisitor(blk); });
}
void
BaseCache::memInvalidate()
{
tags->forEachBlk([this](CacheBlk &blk) { invalidateVisitor(blk); });
}
bool
BaseCache::isDirty() const
{
return tags->anyBlk([](CacheBlk &blk) {
return blk.isSet(CacheBlk::DirtyBit); });
}
bool
BaseCache::coalesce() const
{
return writeAllocator && writeAllocator->coalesce();
}
void
BaseCache::writebackVisitor(CacheBlk &blk)
{
if (blk.isSet(CacheBlk::DirtyBit)) {
assert(blk.isValid());
RequestPtr request = std::make_shared<Request>(
regenerateBlkAddr(&blk), blkSize, 0, Request::funcRequestorId);
request->taskId(blk.getTaskId());
if (blk.isSecure()) {
request->setFlags(Request::SECURE);
}
Packet packet(request, MemCmd::WriteReq);
packet.dataStatic(blk.data);
memSidePort.sendFunctional(&packet);
blk.clearCoherenceBits(CacheBlk::DirtyBit);
}
}
void
BaseCache::invalidateVisitor(CacheBlk &blk)
{
if (blk.isSet(CacheBlk::DirtyBit))
warn_once("Invalidating dirty cache lines. " \
"Expect things to break.\n");
if (blk.isValid()) {
assert(!blk.isSet(CacheBlk::DirtyBit));
invalidateBlock(&blk);
}
}
Tick
BaseCache::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() && !isBlocked()) {
nextReady = std::min(nextReady,
prefetcher->nextPrefetchReadyTime());
}
return nextReady;
}
bool
BaseCache::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());
// if the cache is in write coalescing mode or (additionally) in
// no allocation mode, and we have a write packet with an MSHR
// that is not a whole-line write (due to incompatible flags etc),
// then reset the write mode
if (writeAllocator && writeAllocator->coalesce() && tgt_pkt->isWrite()) {
if (!mshr->isWholeLineWrite()) {
// if we are currently write coalescing, hold on the
// MSHR as many cycles extra as we need to completely
// write a cache line
if (writeAllocator->delay(mshr->blkAddr)) {
Tick delay = blkSize / tgt_pkt->getSize() * clockPeriod();
DPRINTF(CacheVerbose, "Delaying pkt %s %llu ticks to allow "
"for write coalescing\n", tgt_pkt->print(), delay);
mshrQueue.delay(mshr, delay);
return false;
} else {
writeAllocator->reset();
}
} else {
writeAllocator->resetDelay(mshr->blkAddr);
}
}
CacheBlk *blk = tags->findBlock(mshr->blkAddr, mshr->isSecure);
// 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->isWholeLineWrite());
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->isSet(CacheBlk::DirtyBit)) {
// 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->isSet(CacheBlk::DirtyBit)) {
// 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
BaseCache::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
BaseCache::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
BaseCache::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");
}
}
BaseCache::CacheCmdStats::CacheCmdStats(BaseCache &c,
const std::string &name)
: statistics::Group(&c, name.c_str()), cache(c),
ADD_STAT(hits, statistics::units::Count::get(),
("number of " + name + " hits").c_str()),
ADD_STAT(misses, statistics::units::Count::get(),
("number of " + name + " misses").c_str()),
ADD_STAT(hitLatency, statistics::units::Tick::get(),
("number of " + name + " hit ticks").c_str()),
ADD_STAT(missLatency, statistics::units::Tick::get(),
("number of " + name + " miss ticks").c_str()),
ADD_STAT(accesses, statistics::units::Count::get(),
("number of " + name + " accesses(hits+misses)").c_str()),
ADD_STAT(missRate, statistics::units::Ratio::get(),
("miss rate for " + name + " accesses").c_str()),
ADD_STAT(avgMissLatency, statistics::units::Rate<
statistics::units::Tick, statistics::units::Count>::get(),
("average " + name + " miss latency").c_str()),
ADD_STAT(mshrHits, statistics::units::Count::get(),
("number of " + name + " MSHR hits").c_str()),
ADD_STAT(mshrMisses, statistics::units::Count::get(),
("number of " + name + " MSHR misses").c_str()),
ADD_STAT(mshrUncacheable, statistics::units::Count::get(),
("number of " + name + " MSHR uncacheable").c_str()),
ADD_STAT(mshrMissLatency, statistics::units::Tick::get(),
("number of " + name + " MSHR miss ticks").c_str()),
ADD_STAT(mshrUncacheableLatency, statistics::units::Tick::get(),
("number of " + name + " MSHR uncacheable ticks").c_str()),
ADD_STAT(mshrMissRate, statistics::units::Ratio::get(),
("mshr miss rate for " + name + " accesses").c_str()),
ADD_STAT(avgMshrMissLatency, statistics::units::Rate<
statistics::units::Tick, statistics::units::Count>::get(),
("average " + name + " mshr miss latency").c_str()),
ADD_STAT(avgMshrUncacheableLatency, statistics::units::Rate<
statistics::units::Tick, statistics::units::Count>::get(),
("average " + name + " mshr uncacheable latency").c_str())
{
}
void
BaseCache::CacheCmdStats::regStatsFromParent()
{
using namespace statistics;
statistics::Group::regStats();
System *system = cache.system;
const auto max_requestors = system->maxRequestors();
hits
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
hits.subname(i, system->getRequestorName(i));
}
// Miss statistics
misses
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
misses.subname(i, system->getRequestorName(i));
}
// Hit latency statistics
hitLatency
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
hitLatency.subname(i, system->getRequestorName(i));
}
// Miss latency statistics
missLatency
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
missLatency.subname(i, system->getRequestorName(i));
}
// access formulas
accesses.flags(total | nozero | nonan);
accesses = hits + misses;
for (int i = 0; i < max_requestors; i++) {
accesses.subname(i, system->getRequestorName(i));
}
// miss rate formulas
missRate.flags(total | nozero | nonan);
missRate = misses / accesses;
for (int i = 0; i < max_requestors; i++) {
missRate.subname(i, system->getRequestorName(i));
}
// miss latency formulas
avgMissLatency.flags(total | nozero | nonan);
avgMissLatency = missLatency / misses;
for (int i = 0; i < max_requestors; i++) {
avgMissLatency.subname(i, system->getRequestorName(i));
}
// MSHR statistics
// MSHR hit statistics
mshrHits
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
mshrHits.subname(i, system->getRequestorName(i));
}
// MSHR miss statistics
mshrMisses
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
mshrMisses.subname(i, system->getRequestorName(i));
}
// MSHR miss latency statistics
mshrMissLatency
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
mshrMissLatency.subname(i, system->getRequestorName(i));
}
// MSHR uncacheable statistics
mshrUncacheable
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
mshrUncacheable.subname(i, system->getRequestorName(i));
}
// MSHR miss latency statistics
mshrUncacheableLatency
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
mshrUncacheableLatency.subname(i, system->getRequestorName(i));
}
// MSHR miss rate formulas
mshrMissRate.flags(total | nozero | nonan);
mshrMissRate = mshrMisses / accesses;
for (int i = 0; i < max_requestors; i++) {
mshrMissRate.subname(i, system->getRequestorName(i));
}
// mshrMiss latency formulas
avgMshrMissLatency.flags(total | nozero | nonan);
avgMshrMissLatency = mshrMissLatency / mshrMisses;
for (int i = 0; i < max_requestors; i++) {
avgMshrMissLatency.subname(i, system->getRequestorName(i));
}
// mshrUncacheable latency formulas
avgMshrUncacheableLatency.flags(total | nozero | nonan);
avgMshrUncacheableLatency = mshrUncacheableLatency / mshrUncacheable;
for (int i = 0; i < max_requestors; i++) {
avgMshrUncacheableLatency.subname(i, system->getRequestorName(i));
}
}
BaseCache::CacheStats::CacheStats(BaseCache &c)
: statistics::Group(&c), cache(c),
ADD_STAT(demandHits, statistics::units::Count::get(),
"number of demand (read+write) hits"),
ADD_STAT(overallHits, statistics::units::Count::get(),
"number of overall hits"),
ADD_STAT(demandHitLatency, statistics::units::Tick::get(),
"number of demand (read+write) hit ticks"),
ADD_STAT(overallHitLatency, statistics::units::Tick::get(),
"number of overall hit ticks"),
ADD_STAT(demandMisses, statistics::units::Count::get(),
"number of demand (read+write) misses"),
ADD_STAT(overallMisses, statistics::units::Count::get(),
"number of overall misses"),
ADD_STAT(demandMissLatency, statistics::units::Tick::get(),
"number of demand (read+write) miss ticks"),
ADD_STAT(overallMissLatency, statistics::units::Tick::get(),
"number of overall miss ticks"),
ADD_STAT(demandAccesses, statistics::units::Count::get(),
"number of demand (read+write) accesses"),
ADD_STAT(overallAccesses, statistics::units::Count::get(),
"number of overall (read+write) accesses"),
ADD_STAT(demandMissRate, statistics::units::Ratio::get(),
"miss rate for demand accesses"),
ADD_STAT(overallMissRate, statistics::units::Ratio::get(),
"miss rate for overall accesses"),
ADD_STAT(demandAvgMissLatency, statistics::units::Rate<
statistics::units::Tick, statistics::units::Count>::get(),
"average overall miss latency in ticks"),
ADD_STAT(overallAvgMissLatency, statistics::units::Rate<
statistics::units::Tick, statistics::units::Count>::get(),
"average overall miss latency"),
ADD_STAT(blockedCycles, statistics::units::Cycle::get(),
"number of cycles access was blocked"),
ADD_STAT(blockedCauses, statistics::units::Count::get(),
"number of times access was blocked"),
ADD_STAT(avgBlocked, statistics::units::Rate<
statistics::units::Cycle, statistics::units::Count>::get(),
"average number of cycles each access was blocked"),
ADD_STAT(writebacks, statistics::units::Count::get(),
"number of writebacks"),
ADD_STAT(demandMshrHits, statistics::units::Count::get(),
"number of demand (read+write) MSHR hits"),
ADD_STAT(overallMshrHits, statistics::units::Count::get(),
"number of overall MSHR hits"),
ADD_STAT(demandMshrMisses, statistics::units::Count::get(),
"number of demand (read+write) MSHR misses"),
ADD_STAT(overallMshrMisses, statistics::units::Count::get(),
"number of overall MSHR misses"),
ADD_STAT(overallMshrUncacheable, statistics::units::Count::get(),
"number of overall MSHR uncacheable misses"),
ADD_STAT(demandMshrMissLatency, statistics::units::Tick::get(),
"number of demand (read+write) MSHR miss ticks"),
ADD_STAT(overallMshrMissLatency, statistics::units::Tick::get(),
"number of overall MSHR miss ticks"),
ADD_STAT(overallMshrUncacheableLatency, statistics::units::Tick::get(),
"number of overall MSHR uncacheable ticks"),
ADD_STAT(demandMshrMissRate, statistics::units::Ratio::get(),
"mshr miss ratio for demand accesses"),
ADD_STAT(overallMshrMissRate, statistics::units::Ratio::get(),
"mshr miss ratio for overall accesses"),
ADD_STAT(demandAvgMshrMissLatency, statistics::units::Rate<
statistics::units::Tick, statistics::units::Count>::get(),
"average overall mshr miss latency"),
ADD_STAT(overallAvgMshrMissLatency, statistics::units::Rate<
statistics::units::Tick, statistics::units::Count>::get(),
"average overall mshr miss latency"),
ADD_STAT(overallAvgMshrUncacheableLatency, statistics::units::Rate<
statistics::units::Tick, statistics::units::Count>::get(),
"average overall mshr uncacheable latency"),
ADD_STAT(replacements, statistics::units::Count::get(),
"number of replacements"),
ADD_STAT(dataExpansions, statistics::units::Count::get(),
"number of data expansions"),
ADD_STAT(dataContractions, statistics::units::Count::get(),
"number of data contractions"),
cmd(MemCmd::NUM_MEM_CMDS)
{
for (int idx = 0; idx < MemCmd::NUM_MEM_CMDS; ++idx)
cmd[idx].reset(new CacheCmdStats(c, MemCmd(idx).toString()));
}
void
BaseCache::CacheStats::regStats()
{
using namespace statistics;
statistics::Group::regStats();
System *system = cache.system;
const auto max_requestors = system->maxRequestors();
for (auto &cs : cmd)
cs->regStatsFromParent();
// These macros make it easier to sum the right subset of commands and
// to change the subset of commands that are considered "demand" vs
// "non-demand"
#define SUM_DEMAND(s) \
(cmd[MemCmd::ReadReq]->s + cmd[MemCmd::WriteReq]->s + \
cmd[MemCmd::WriteLineReq]->s + cmd[MemCmd::ReadExReq]->s + \
cmd[MemCmd::ReadCleanReq]->s + cmd[MemCmd::ReadSharedReq]->s)
// should writebacks be included here? prior code was inconsistent...
#define SUM_NON_DEMAND(s) \
(cmd[MemCmd::SoftPFReq]->s + cmd[MemCmd::HardPFReq]->s + \
cmd[MemCmd::SoftPFExReq]->s)
demandHits.flags(total | nozero | nonan);
demandHits = SUM_DEMAND(hits);
for (int i = 0; i < max_requestors; i++) {
demandHits.subname(i, system->getRequestorName(i));
}
overallHits.flags(total | nozero | nonan);
overallHits = demandHits + SUM_NON_DEMAND(hits);
for (int i = 0; i < max_requestors; i++) {
overallHits.subname(i, system->getRequestorName(i));
}
demandMisses.flags(total | nozero | nonan);
demandMisses = SUM_DEMAND(misses);
for (int i = 0; i < max_requestors; i++) {
demandMisses.subname(i, system->getRequestorName(i));
}
overallMisses.flags(total | nozero | nonan);
overallMisses = demandMisses + SUM_NON_DEMAND(misses);
for (int i = 0; i < max_requestors; i++) {
overallMisses.subname(i, system->getRequestorName(i));
}
demandMissLatency.flags(total | nozero | nonan);
demandMissLatency = SUM_DEMAND(missLatency);
for (int i = 0; i < max_requestors; i++) {
demandMissLatency.subname(i, system->getRequestorName(i));
}
overallMissLatency.flags(total | nozero | nonan);
overallMissLatency = demandMissLatency + SUM_NON_DEMAND(missLatency);
for (int i = 0; i < max_requestors; i++) {
overallMissLatency.subname(i, system->getRequestorName(i));
}
demandHitLatency.flags(total | nozero | nonan);
demandHitLatency = SUM_DEMAND(hitLatency);
for (int i = 0; i < max_requestors; i++) {
demandHitLatency.subname(i, system->getRequestorName(i));
}
overallHitLatency.flags(total | nozero | nonan);
overallHitLatency = demandHitLatency + SUM_NON_DEMAND(hitLatency);
for (int i = 0; i < max_requestors; i++) {
overallHitLatency.subname(i, system->getRequestorName(i));
}
demandAccesses.flags(total | nozero | nonan);
demandAccesses = demandHits + demandMisses;
for (int i = 0; i < max_requestors; i++) {
demandAccesses.subname(i, system->getRequestorName(i));
}
overallAccesses.flags(total | nozero | nonan);
overallAccesses = overallHits + overallMisses;
for (int i = 0; i < max_requestors; i++) {
overallAccesses.subname(i, system->getRequestorName(i));
}
demandMissRate.flags(total | nozero | nonan);
demandMissRate = demandMisses / demandAccesses;
for (int i = 0; i < max_requestors; i++) {
demandMissRate.subname(i, system->getRequestorName(i));
}
overallMissRate.flags(total | nozero | nonan);
overallMissRate = overallMisses / overallAccesses;
for (int i = 0; i < max_requestors; i++) {
overallMissRate.subname(i, system->getRequestorName(i));
}
demandAvgMissLatency.flags(total | nozero | nonan);
demandAvgMissLatency = demandMissLatency / demandMisses;
for (int i = 0; i < max_requestors; i++) {
demandAvgMissLatency.subname(i, system->getRequestorName(i));
}
overallAvgMissLatency.flags(total | nozero | nonan);
overallAvgMissLatency = overallMissLatency / overallMisses;
for (int i = 0; i < max_requestors; i++) {
overallAvgMissLatency.subname(i, system->getRequestorName(i));
}
blockedCycles.init(NUM_BLOCKED_CAUSES);
blockedCycles
.subname(Blocked_NoMSHRs, "no_mshrs")
.subname(Blocked_NoTargets, "no_targets")
;
blockedCauses.init(NUM_BLOCKED_CAUSES);
blockedCauses
.subname(Blocked_NoMSHRs, "no_mshrs")
.subname(Blocked_NoTargets, "no_targets")
;
avgBlocked
.subname(Blocked_NoMSHRs, "no_mshrs")
.subname(Blocked_NoTargets, "no_targets")
;
avgBlocked = blockedCycles / blockedCauses;
writebacks
.init(max_requestors)
.flags(total | nozero | nonan)
;
for (int i = 0; i < max_requestors; i++) {
writebacks.subname(i, system->getRequestorName(i));
}
demandMshrHits.flags(total | nozero | nonan);
demandMshrHits = SUM_DEMAND(mshrHits);
for (int i = 0; i < max_requestors; i++) {
demandMshrHits.subname(i, system->getRequestorName(i));
}
overallMshrHits.flags(total | nozero | nonan);
overallMshrHits = demandMshrHits + SUM_NON_DEMAND(mshrHits);
for (int i = 0; i < max_requestors; i++) {
overallMshrHits.subname(i, system->getRequestorName(i));
}
demandMshrMisses.flags(total | nozero | nonan);
demandMshrMisses = SUM_DEMAND(mshrMisses);
for (int i = 0; i < max_requestors; i++) {
demandMshrMisses.subname(i, system->getRequestorName(i));
}
overallMshrMisses.flags(total | nozero | nonan);
overallMshrMisses = demandMshrMisses + SUM_NON_DEMAND(mshrMisses);
for (int i = 0; i < max_requestors; i++) {
overallMshrMisses.subname(i, system->getRequestorName(i));
}
demandMshrMissLatency.flags(total | nozero | nonan);
demandMshrMissLatency = SUM_DEMAND(mshrMissLatency);
for (int i = 0; i < max_requestors; i++) {
demandMshrMissLatency.subname(i, system->getRequestorName(i));
}
overallMshrMissLatency.flags(total | nozero | nonan);
overallMshrMissLatency =
demandMshrMissLatency + SUM_NON_DEMAND(mshrMissLatency);
for (int i = 0; i < max_requestors; i++) {
overallMshrMissLatency.subname(i, system->getRequestorName(i));
}
overallMshrUncacheable.flags(total | nozero | nonan);
overallMshrUncacheable =
SUM_DEMAND(mshrUncacheable) + SUM_NON_DEMAND(mshrUncacheable);
for (int i = 0; i < max_requestors; i++) {
overallMshrUncacheable.subname(i, system->getRequestorName(i));
}
overallMshrUncacheableLatency.flags(total | nozero | nonan);
overallMshrUncacheableLatency =
SUM_DEMAND(mshrUncacheableLatency) +
SUM_NON_DEMAND(mshrUncacheableLatency);
for (int i = 0; i < max_requestors; i++) {
overallMshrUncacheableLatency.subname(i, system->getRequestorName(i));
}
demandMshrMissRate.flags(total | nozero | nonan);
demandMshrMissRate = demandMshrMisses / demandAccesses;
for (int i = 0; i < max_requestors; i++) {
demandMshrMissRate.subname(i, system->getRequestorName(i));
}
overallMshrMissRate.flags(total | nozero | nonan);
overallMshrMissRate = overallMshrMisses / overallAccesses;
for (int i = 0; i < max_requestors; i++) {
overallMshrMissRate.subname(i, system->getRequestorName(i));
}
demandAvgMshrMissLatency.flags(total | nozero | nonan);
demandAvgMshrMissLatency = demandMshrMissLatency / demandMshrMisses;
for (int i = 0; i < max_requestors; i++) {
demandAvgMshrMissLatency.subname(i, system->getRequestorName(i));
}
overallAvgMshrMissLatency.flags(total | nozero | nonan);
overallAvgMshrMissLatency = overallMshrMissLatency / overallMshrMisses;
for (int i = 0; i < max_requestors; i++) {
overallAvgMshrMissLatency.subname(i, system->getRequestorName(i));
}
overallAvgMshrUncacheableLatency.flags(total | nozero | nonan);
overallAvgMshrUncacheableLatency =
overallMshrUncacheableLatency / overallMshrUncacheable;
for (int i = 0; i < max_requestors; i++) {
overallAvgMshrUncacheableLatency.subname(i,
system->getRequestorName(i));
}
dataExpansions.flags(nozero | nonan);
dataContractions.flags(nozero | nonan);
}
void
BaseCache::regProbePoints()
{
ppHit = new ProbePointArg<PacketPtr>(this->getProbeManager(), "Hit");
ppMiss = new ProbePointArg<PacketPtr>(this->getProbeManager(), "Miss");
ppFill = new ProbePointArg<PacketPtr>(this->getProbeManager(), "Fill");
ppDataUpdate =
new ProbePointArg<DataUpdate>(this->getProbeManager(), "Data Update");
}
///////////////
//
// CpuSidePort
//
///////////////
bool
BaseCache::CpuSidePort::recvTimingSnoopResp(PacketPtr pkt)
{
// Snoops shouldn't happen when bypassing caches
assert(!cache->system->bypassCaches());
assert(pkt->isResponse());
// Express snoop responses from requestor to responder, e.g., from L1 to L2
cache->recvTimingSnoopResp(pkt);
return true;
}
bool
BaseCache::CpuSidePort::tryTiming(PacketPtr pkt)
{
if (cache->system->bypassCaches() || pkt->isExpressSnoop()) {
// always let express snoop packets through even if blocked
return true;
} else if (blocked || mustSendRetry) {
// either already committed to send a retry, or blocked
mustSendRetry = true;
return false;
}
mustSendRetry = false;
return true;
}
bool
BaseCache::CpuSidePort::recvTimingReq(PacketPtr pkt)
{
assert(pkt->isRequest());
if (cache->system->bypassCaches()) {
// Just forward the packet if caches are disabled.
// @todo This should really enqueue the packet rather
[[maybe_unused]] bool success = cache->memSidePort.sendTimingReq(pkt);
assert(success);
return true;
} else if (tryTiming(pkt)) {
cache->recvTimingReq(pkt);
return true;
}
return false;
}
Tick
BaseCache::CpuSidePort::recvAtomic(PacketPtr pkt)
{
if (cache->system->bypassCaches()) {
// Forward the request if the system is in cache bypass mode.
return cache->memSidePort.sendAtomic(pkt);
} else {
return cache->recvAtomic(pkt);
}
}
void
BaseCache::CpuSidePort::recvFunctional(PacketPtr pkt)
{
if (cache->system->bypassCaches()) {
// 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.
cache->memSidePort.sendFunctional(pkt);
return;
}
// functional request
cache->functionalAccess(pkt, true);
}
AddrRangeList
BaseCache::CpuSidePort::getAddrRanges() const
{
return cache->getAddrRanges();
}
BaseCache::
CpuSidePort::CpuSidePort(const std::string &_name, BaseCache *_cache,
const std::string &_label)
: CacheResponsePort(_name, _cache, _label), cache(_cache)
{
}
///////////////
//
// MemSidePort
//
///////////////
bool
BaseCache::MemSidePort::recvTimingResp(PacketPtr pkt)
{
cache->recvTimingResp(pkt);
return true;
}
// Express snooping requests to memside port
void
BaseCache::MemSidePort::recvTimingSnoopReq(PacketPtr pkt)
{
// Snoops shouldn't happen when bypassing caches
assert(!cache->system->bypassCaches());
// handle snooping requests
cache->recvTimingSnoopReq(pkt);
}
Tick
BaseCache::MemSidePort::recvAtomicSnoop(PacketPtr pkt)
{
// Snoops shouldn't happen when bypassing caches
assert(!cache->system->bypassCaches());
return cache->recvAtomicSnoop(pkt);
}
void
BaseCache::MemSidePort::recvFunctionalSnoop(PacketPtr pkt)
{
// Snoops shouldn't happen when bypassing caches
assert(!cache->system->bypassCaches());
// 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
BaseCache::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->getTarget()->pkt)) {
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());
}
}
BaseCache::MemSidePort::MemSidePort(const std::string &_name,
BaseCache *_cache,
const std::string &_label)
: CacheRequestPort(_name, _cache, _reqQueue, _snoopRespQueue),
_reqQueue(*_cache, *this, _snoopRespQueue, _label),
_snoopRespQueue(*_cache, *this, true, _label), cache(_cache)
{
}
void
WriteAllocator::updateMode(Addr write_addr, unsigned write_size,
Addr blk_addr)
{
// check if we are continuing where the last write ended
if (nextAddr == write_addr) {
delayCtr[blk_addr] = delayThreshold;
// stop if we have already saturated
if (mode != WriteMode::NO_ALLOCATE) {
byteCount += write_size;
// switch to streaming mode if we have passed the lower
// threshold
if (mode == WriteMode::ALLOCATE &&
byteCount > coalesceLimit) {
mode = WriteMode::COALESCE;
DPRINTF(Cache, "Switched to write coalescing\n");
} else if (mode == WriteMode::COALESCE &&
byteCount > noAllocateLimit) {
// and continue and switch to non-allocating mode if we
// pass the upper threshold
mode = WriteMode::NO_ALLOCATE;
DPRINTF(Cache, "Switched to write-no-allocate\n");
}
}
} else {
// we did not see a write matching the previous one, start
// over again
byteCount = write_size;
mode = WriteMode::ALLOCATE;
resetDelay(blk_addr);
}
nextAddr = write_addr + write_size;
}
} // namespace gem5