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/*
* Copyright (c) 2012-2013, 2015-2016, 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
* 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) 2003-2005 The Regents of The University of Michigan
* 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,
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* 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.
*/
/**
* @file
* Declares a basic cache interface BaseCache.
*/
#ifndef __MEM_CACHE_BASE_HH__
#define __MEM_CACHE_BASE_HH__
#include <cassert>
#include <cstdint>
#include <string>
#include "base/addr_range.hh"
#include "base/compiler.hh"
#include "base/statistics.hh"
#include "base/trace.hh"
#include "base/types.hh"
#include "debug/Cache.hh"
#include "debug/CachePort.hh"
#include "enums/Clusivity.hh"
#include "mem/cache/cache_blk.hh"
#include "mem/cache/compressors/base.hh"
#include "mem/cache/mshr_queue.hh"
#include "mem/cache/tags/base.hh"
#include "mem/cache/write_queue.hh"
#include "mem/cache/write_queue_entry.hh"
#include "mem/packet.hh"
#include "mem/packet_queue.hh"
#include "mem/qport.hh"
#include "mem/request.hh"
#include "params/WriteAllocator.hh"
#include "sim/clocked_object.hh"
#include "sim/eventq.hh"
#include "sim/probe/probe.hh"
#include "sim/serialize.hh"
#include "sim/sim_exit.hh"
#include "sim/system.hh"
namespace gem5
{
GEM5_DEPRECATED_NAMESPACE(Prefetcher, prefetch);
namespace prefetch
{
class Base;
}
class MSHR;
class RequestPort;
class QueueEntry;
struct BaseCacheParams;
/**
* A basic cache interface. Implements some common functions for speed.
*/
class BaseCache : public ClockedObject
{
protected:
/**
* Indexes to enumerate the MSHR queues.
*/
enum MSHRQueueIndex
{
MSHRQueue_MSHRs,
MSHRQueue_WriteBuffer
};
public:
/**
* Reasons for caches to be blocked.
*/
enum BlockedCause
{
Blocked_NoMSHRs = MSHRQueue_MSHRs,
Blocked_NoWBBuffers = MSHRQueue_WriteBuffer,
Blocked_NoTargets,
NUM_BLOCKED_CAUSES
};
/**
* A data contents update is composed of the updated block's address,
* the old contents, and the new contents.
* @sa ppDataUpdate
*/
struct DataUpdate
{
/** The updated block's address. */
Addr addr;
/** Whether the block belongs to the secure address space. */
bool isSecure;
/** The stale data contents. If zero-sized this update is a fill. */
std::vector<uint64_t> oldData;
/** The new data contents. If zero-sized this is an invalidation. */
std::vector<uint64_t> newData;
DataUpdate(Addr _addr, bool is_secure)
: addr(_addr), isSecure(is_secure), oldData(), newData()
{
}
};
protected:
/**
* A cache request port is used for the memory-side port of the
* cache, and in addition to the basic timing port that only sends
* response packets through a transmit list, it also offers the
* ability to schedule and send request packets (requests &
* writebacks). The send event is scheduled through schedSendEvent,
* and the sendDeferredPacket of the timing port is modified to
* consider both the transmit list and the requests from the MSHR.
*/
class CacheRequestPort : public QueuedRequestPort
{
public:
/**
* Schedule a send of a request packet (from the MSHR). Note
* that we could already have a retry outstanding.
*/
void schedSendEvent(Tick time)
{
DPRINTF(CachePort, "Scheduling send event at %llu\n", time);
reqQueue.schedSendEvent(time);
}
protected:
CacheRequestPort(const std::string &_name, BaseCache *_cache,
ReqPacketQueue &_reqQueue,
SnoopRespPacketQueue &_snoopRespQueue) :
QueuedRequestPort(_name, _cache, _reqQueue, _snoopRespQueue)
{ }
/**
* Memory-side port always snoops.
*
* @return always true
*/
virtual bool isSnooping() const { return true; }
};
/**
* Override the default behaviour of sendDeferredPacket to enable
* the memory-side cache port to also send requests based on the
* current MSHR status. This queue has a pointer to our specific
* cache implementation and is used by the MemSidePort.
*/
class CacheReqPacketQueue : public ReqPacketQueue
{
protected:
BaseCache &cache;
SnoopRespPacketQueue &snoopRespQueue;
public:
CacheReqPacketQueue(BaseCache &cache, RequestPort &port,
SnoopRespPacketQueue &snoop_resp_queue,
const std::string &label) :
ReqPacketQueue(cache, port, label), cache(cache),
snoopRespQueue(snoop_resp_queue) { }
/**
* Override the normal sendDeferredPacket and do not only
* consider the transmit list (used for responses), but also
* requests.
*/
virtual void sendDeferredPacket();
/**
* Check if there is a conflicting snoop response about to be
* send out, and if so simply stall any requests, and schedule
* a send event at the same time as the next snoop response is
* being sent out.
*
* @param pkt The packet to check for conflicts against.
*/
bool checkConflictingSnoop(const PacketPtr pkt)
{
if (snoopRespQueue.checkConflict(pkt, cache.blkSize)) {
DPRINTF(CachePort, "Waiting for snoop response to be "
"sent\n");
Tick when = snoopRespQueue.deferredPacketReadyTime();
schedSendEvent(when);
return true;
}
return false;
}
};
/**
* The memory-side port extends the base cache request port with
* access functions for functional, atomic and timing snoops.
*/
class MemSidePort : public CacheRequestPort
{
private:
/** The cache-specific queue. */
CacheReqPacketQueue _reqQueue;
SnoopRespPacketQueue _snoopRespQueue;
// a pointer to our specific cache implementation
BaseCache *cache;
protected:
virtual void recvTimingSnoopReq(PacketPtr pkt);
virtual bool recvTimingResp(PacketPtr pkt);
virtual Tick recvAtomicSnoop(PacketPtr pkt);
virtual void recvFunctionalSnoop(PacketPtr pkt);
public:
MemSidePort(const std::string &_name, BaseCache *_cache,
const std::string &_label);
};
/**
* A cache response port is used for the CPU-side port of the cache,
* and it is basically a simple timing port that uses a transmit
* list for responses to the CPU (or connected requestor). In
* addition, it has the functionality to block the port for
* incoming requests. If blocked, the port will issue a retry once
* unblocked.
*/
class CacheResponsePort : public QueuedResponsePort
{
public:
/** Do not accept any new requests. */
void setBlocked();
/** Return to normal operation and accept new requests. */
void clearBlocked();
bool isBlocked() const { return blocked; }
protected:
CacheResponsePort(const std::string &_name, BaseCache *_cache,
const std::string &_label);
/** A normal packet queue used to store responses. */
RespPacketQueue queue;
bool blocked;
bool mustSendRetry;
private:
void processSendRetry();
EventFunctionWrapper sendRetryEvent;
};
/**
* The CPU-side port extends the base cache response port with access
* functions for functional, atomic and timing requests.
*/
class CpuSidePort : public CacheResponsePort
{
private:
// a pointer to our specific cache implementation
BaseCache *cache;
protected:
virtual bool recvTimingSnoopResp(PacketPtr pkt) override;
virtual bool tryTiming(PacketPtr pkt) override;
virtual bool recvTimingReq(PacketPtr pkt) override;
virtual Tick recvAtomic(PacketPtr pkt) override;
virtual void recvFunctional(PacketPtr pkt) override;
virtual AddrRangeList getAddrRanges() const override;
public:
CpuSidePort(const std::string &_name, BaseCache *_cache,
const std::string &_label);
};
CpuSidePort cpuSidePort;
MemSidePort memSidePort;
protected:
/** Miss status registers */
MSHRQueue mshrQueue;
/** Write/writeback buffer */
WriteQueue writeBuffer;
/** Tag and data Storage */
BaseTags *tags;
/** Compression method being used. */
compression::Base* compressor;
/** Prefetcher */
prefetch::Base *prefetcher;
/** To probe when a cache hit occurs */
ProbePointArg<PacketPtr> *ppHit;
/** To probe when a cache miss occurs */
ProbePointArg<PacketPtr> *ppMiss;
/** To probe when a cache fill occurs */
ProbePointArg<PacketPtr> *ppFill;
/**
* To probe when the contents of a block are updated. Content updates
* include data fills, overwrites, and invalidations, which means that
* this probe partially overlaps with other probes.
*/
ProbePointArg<DataUpdate> *ppDataUpdate;
/**
* The writeAllocator drive optimizations for streaming writes.
* It first determines whether a WriteReq MSHR should be delayed,
* thus ensuring that we wait longer in cases when we are write
* coalescing and allowing all the bytes of the line to be written
* before the MSHR packet is sent downstream. This works in unison
* with the tracking in the MSHR to check if the entire line is
* written. The write mode also affects the behaviour on filling
* any whole-line writes. Normally the cache allocates the line
* when receiving the InvalidateResp, but after seeing enough
* consecutive lines we switch to using the tempBlock, and thus
* end up not allocating the line, and instead turning the
* whole-line write into a writeback straight away.
*/
WriteAllocator * const writeAllocator;
/**
* Temporary cache block for occasional transitory use. We use
* the tempBlock to fill when allocation fails (e.g., when there
* is an outstanding request that accesses the victim block) or
* when we want to avoid allocation (e.g., exclusive caches)
*/
TempCacheBlk *tempBlock;
/**
* Upstream caches need this packet until true is returned, so
* hold it for deletion until a subsequent call
*/
std::unique_ptr<Packet> pendingDelete;
/**
* Mark a request as in service (sent downstream in the memory
* system), effectively making this MSHR the ordering point.
*/
void markInService(MSHR *mshr, bool pending_modified_resp)
{
bool wasFull = mshrQueue.isFull();
mshrQueue.markInService(mshr, pending_modified_resp);
if (wasFull && !mshrQueue.isFull()) {
clearBlocked(Blocked_NoMSHRs);
}
}
void markInService(WriteQueueEntry *entry)
{
bool wasFull = writeBuffer.isFull();
writeBuffer.markInService(entry);
if (wasFull && !writeBuffer.isFull()) {
clearBlocked(Blocked_NoWBBuffers);
}
}
/**
* Determine whether we should allocate on a fill or not. If this
* cache is mostly inclusive with regards to the upstream cache(s)
* we always allocate (for any non-forwarded and cacheable
* requests). In the case of a mostly exclusive cache, we allocate
* on fill if the packet did not come from a cache, thus if we:
* are dealing with a whole-line write (the latter behaves much
* like a writeback), the original target packet came from a
* non-caching source, or if we are performing a prefetch or LLSC.
*
* @param cmd Command of the incoming requesting packet
* @return Whether we should allocate on the fill
*/
inline bool allocOnFill(MemCmd cmd) const
{
return clusivity == enums::mostly_incl ||
cmd == MemCmd::WriteLineReq ||
cmd == MemCmd::ReadReq ||
cmd == MemCmd::WriteReq ||
cmd.isPrefetch() ||
cmd.isLLSC();
}
/**
* Regenerate block address using tags.
* Block address regeneration depends on whether we're using a temporary
* block or not.
*
* @param blk The block to regenerate address.
* @return The block's address.
*/
Addr regenerateBlkAddr(CacheBlk* blk);
/**
* Calculate latency of accesses that only touch the tag array.
* @sa calculateAccessLatency
*
* @param delay The delay until the packet's metadata is present.
* @param lookup_lat Latency of the respective tag lookup.
* @return The number of ticks that pass due to a tag-only access.
*/
Cycles calculateTagOnlyLatency(const uint32_t delay,
const Cycles lookup_lat) const;
/**
* Calculate access latency in ticks given a tag lookup latency, and
* whether access was a hit or miss.
*
* @param blk The cache block that was accessed.
* @param delay The delay until the packet's metadata is present.
* @param lookup_lat Latency of the respective tag lookup.
* @return The number of ticks that pass due to a block access.
*/
Cycles calculateAccessLatency(const CacheBlk* blk, const uint32_t delay,
const Cycles lookup_lat) const;
/**
* Does all the processing necessary to perform the provided request.
* @param pkt The memory request to perform.
* @param blk The cache block to be updated.
* @param lat The latency of the access.
* @param writebacks List for any writebacks that need to be performed.
* @return Boolean indicating whether the request was satisfied.
*/
virtual bool access(PacketPtr pkt, CacheBlk *&blk, Cycles &lat,
PacketList &writebacks);
/*
* Handle a timing request that hit in the cache
*
* @param ptk The request packet
* @param blk The referenced block
* @param request_time The tick at which the block lookup is compete
*/
virtual void handleTimingReqHit(PacketPtr pkt, CacheBlk *blk,
Tick request_time);
/*
* Handle a timing request that missed in the cache
*
* Implementation specific handling for different cache
* implementations
*
* @param ptk The request packet
* @param blk The referenced block
* @param forward_time The tick at which we can process dependent requests
* @param request_time The tick at which the block lookup is compete
*/
virtual void handleTimingReqMiss(PacketPtr pkt, CacheBlk *blk,
Tick forward_time,
Tick request_time) = 0;
/*
* Handle a timing request that missed in the cache
*
* Common functionality across different cache implementations
*
* @param ptk The request packet
* @param blk The referenced block
* @param mshr Any existing mshr for the referenced cache block
* @param forward_time The tick at which we can process dependent requests
* @param request_time The tick at which the block lookup is compete
*/
void handleTimingReqMiss(PacketPtr pkt, MSHR *mshr, CacheBlk *blk,
Tick forward_time, Tick request_time);
/**
* Performs the access specified by the request.
* @param pkt The request to perform.
*/
virtual void recvTimingReq(PacketPtr pkt);
/**
* Handling the special case of uncacheable write responses to
* make recvTimingResp less cluttered.
*/
void handleUncacheableWriteResp(PacketPtr pkt);
/**
* Service non-deferred MSHR targets using the received response
*
* Iterates through the list of targets that can be serviced with
* the current response.
*
* @param mshr The MSHR that corresponds to the reponse
* @param pkt The response packet
* @param blk The reference block
*/
virtual void serviceMSHRTargets(MSHR *mshr, const PacketPtr pkt,
CacheBlk *blk) = 0;
/**
* Handles a response (cache line fill/write ack) from the bus.
* @param pkt The response packet
*/
virtual void recvTimingResp(PacketPtr pkt);
/**
* Snoops bus transactions to maintain coherence.
* @param pkt The current bus transaction.
*/
virtual void recvTimingSnoopReq(PacketPtr pkt) = 0;
/**
* Handle a snoop response.
* @param pkt Snoop response packet
*/
virtual void recvTimingSnoopResp(PacketPtr pkt) = 0;
/**
* Handle a request in atomic mode that missed in this cache
*
* Creates a downstream request, sends it to the memory below and
* handles the response. As we are in atomic mode all operations
* are performed immediately.
*
* @param pkt The packet with the requests
* @param blk The referenced block
* @param writebacks A list with packets for any performed writebacks
* @return Cycles for handling the request
*/
virtual Cycles handleAtomicReqMiss(PacketPtr pkt, CacheBlk *&blk,
PacketList &writebacks) = 0;
/**
* Performs the access specified by the request.
* @param pkt The request to perform.
* @return The number of ticks required for the access.
*/
virtual Tick recvAtomic(PacketPtr pkt);
/**
* Snoop for the provided request in the cache and return the estimated
* time taken.
* @param pkt The memory request to snoop
* @return The number of ticks required for the snoop.
*/
virtual Tick recvAtomicSnoop(PacketPtr pkt) = 0;
/**
* Performs the access specified by the request.
*
* @param pkt The request to perform.
* @param fromCpuSide from the CPU side port or the memory side port
*/
virtual void functionalAccess(PacketPtr pkt, bool from_cpu_side);
/**
* Update the data contents of a block. When no packet is provided no
* data will be written to the block, which means that this was likely
* triggered by an invalidation.
*
* @param blk The block being updated.
* @param cpkt The packet containing the new data.
* @param has_old_data Whether this block had data previously.
*/
void updateBlockData(CacheBlk *blk, const PacketPtr cpkt,
bool has_old_data);
/**
* Handle doing the Compare and Swap function for SPARC.
*/
void cmpAndSwap(CacheBlk *blk, PacketPtr pkt);
/**
* Return the next queue entry to service, either a pending miss
* from the MSHR queue, a buffered write from the write buffer, or
* something from the prefetcher. This function is responsible
* for prioritizing among those sources on the fly.
*/
QueueEntry* getNextQueueEntry();
/**
* Insert writebacks into the write buffer
*/
virtual void doWritebacks(PacketList& writebacks, Tick forward_time) = 0;
/**
* Send writebacks down the memory hierarchy in atomic mode
*/
virtual void doWritebacksAtomic(PacketList& writebacks) = 0;
/**
* Create an appropriate downstream bus request packet.
*
* Creates a new packet with the request to be send to the memory
* below, or nullptr if the current request in cpu_pkt should just
* be forwarded on.
*
* @param cpu_pkt The miss packet that needs to be satisfied.
* @param blk The referenced block, can be nullptr.
* @param needs_writable Indicates that the block must be writable
* even if the request in cpu_pkt doesn't indicate that.
* @param is_whole_line_write True if there are writes for the
* whole line
* @return A packet send to the memory below
*/
virtual PacketPtr createMissPacket(PacketPtr cpu_pkt, CacheBlk *blk,
bool needs_writable,
bool is_whole_line_write) const = 0;
/**
* Determine if clean lines should be written back or not. In
* cases where a downstream cache is mostly inclusive we likely
* want it to act as a victim cache also for lines that have not
* been modified. Hence, we cannot simply drop the line (or send a
* clean evict), but rather need to send the actual data.
*/
const bool writebackClean;
/**
* Writebacks from the tempBlock, resulting on the response path
* in atomic mode, must happen after the call to recvAtomic has
* finished (for the right ordering of the packets). We therefore
* need to hold on to the packets, and have a method and an event
* to send them.
*/
PacketPtr tempBlockWriteback;
/**
* Send the outstanding tempBlock writeback. To be called after
* recvAtomic finishes in cases where the block we filled is in
* fact the tempBlock, and now needs to be written back.
*/
void writebackTempBlockAtomic() {
assert(tempBlockWriteback != nullptr);
PacketList writebacks{tempBlockWriteback};
doWritebacksAtomic(writebacks);
tempBlockWriteback = nullptr;
}
/**
* An event to writeback the tempBlock after recvAtomic
* finishes. To avoid other calls to recvAtomic getting in
* between, we create this event with a higher priority.
*/
EventFunctionWrapper writebackTempBlockAtomicEvent;
/**
* When a block is overwriten, its compression information must be updated,
* and it may need to be recompressed. If the compression size changes, the
* block may either become smaller, in which case there is no side effect,
* or bigger (data expansion; fat write), in which case the block might not
* fit in its current location anymore. If that happens, there are usually
* two options to be taken:
*
* - The co-allocated blocks must be evicted to make room for this block.
* Simpler, but ignores replacement data.
* - The block itself is moved elsewhere (used in policies where the CF
* determines the location of the block).
*
* This implementation uses the first approach.
*
* Notice that this is only called for writebacks, which means that L1
* caches (which see regular Writes), do not support compression.
* @sa CompressedTags
*
* @param blk The block to be overwriten.
* @param data A pointer to the data to be compressed (blk's new data).
* @param writebacks List for any writebacks that need to be performed.
* @return Whether operation is successful or not.
*/
bool updateCompressionData(CacheBlk *&blk, const uint64_t* data,
PacketList &writebacks);
/**
* Perform any necessary updates to the block and perform any data
* exchange between the packet and the block. The flags of the
* packet are also set accordingly.
*
* @param pkt Request packet from upstream that hit a block
* @param blk Cache block that the packet hit
* @param deferred_response Whether this request originally missed
* @param pending_downgrade Whether the writable flag is to be removed
*/
virtual void satisfyRequest(PacketPtr pkt, CacheBlk *blk,
bool deferred_response = false,
bool pending_downgrade = false);
/**
* Maintain the clusivity of this cache by potentially
* invalidating a block. This method works in conjunction with
* satisfyRequest, but is separate to allow us to handle all MSHR
* targets before potentially dropping a block.
*
* @param from_cache Whether we have dealt with a packet from a cache
* @param blk The block that should potentially be dropped
*/
void maintainClusivity(bool from_cache, CacheBlk *blk);
/**
* Try to evict the given blocks. If any of them is a transient eviction,
* that is, the block is present in the MSHR queue all evictions are
* cancelled since handling such cases has not been implemented.
*
* @param evict_blks Blocks marked for eviction.
* @param writebacks List for any writebacks that need to be performed.
* @return False if any of the evicted blocks is in transient state.
*/
bool handleEvictions(std::vector<CacheBlk*> &evict_blks,
PacketList &writebacks);
/**
* Handle a fill operation caused by a received packet.
*
* Populates a cache block and handles all outstanding requests for the
* satisfied fill request. This version takes two memory requests. One
* contains the fill data, the other is an optional target to satisfy.
* 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).
*
* @param pkt The memory request with the fill data.
* @param blk The cache block if it already exists.
* @param writebacks List for any writebacks that need to be performed.
* @param allocate Whether to allocate a block or use the temp block
* @return Pointer to the new cache block.
*/
CacheBlk *handleFill(PacketPtr pkt, CacheBlk *blk,
PacketList &writebacks, bool allocate);
/**
* Allocate a new block and perform any necessary writebacks
*
* Find a victim block and if necessary prepare writebacks for any
* existing data. May return nullptr if there are no replaceable
* blocks. If a replaceable block is found, it inserts the new block in
* its place. The new block, however, is not set as valid yet.
*
* @param pkt Packet holding the address to update
* @param writebacks A list of writeback packets for the evicted blocks
* @return the allocated block
*/
CacheBlk *allocateBlock(const PacketPtr pkt, PacketList &writebacks);
/**
* Evict a cache block.
*
* Performs a writeback if necesssary and invalidates the block
*
* @param blk Block to invalidate
* @return A packet with the writeback, can be nullptr
*/
[[nodiscard]] virtual PacketPtr evictBlock(CacheBlk *blk) = 0;
/**
* Evict a cache block.
*
* Performs a writeback if necesssary and invalidates the block
*
* @param blk Block to invalidate
* @param writebacks Return a list of packets with writebacks
*/
void evictBlock(CacheBlk *blk, PacketList &writebacks);
/**
* Invalidate a cache block.
*
* @param blk Block to invalidate
*/
void invalidateBlock(CacheBlk *blk);
/**
* Create a writeback request for the given block.
*
* @param blk The block to writeback.
* @return The writeback request for the block.
*/
PacketPtr writebackBlk(CacheBlk *blk);
/**
* Create a writeclean request for the given block.
*
* Creates a request that writes the block to the cache below
* without evicting the block from the current cache.
*
* @param blk The block to write clean.
* @param dest The destination of the write clean operation.
* @param id Use the given packet id for the write clean operation.
* @return The generated write clean packet.
*/
PacketPtr writecleanBlk(CacheBlk *blk, Request::Flags dest, PacketId id);
/**
* Write back dirty blocks in the cache using functional accesses.
*/
virtual void memWriteback() override;
/**
* Invalidates all blocks in the cache.
*
* @warn Dirty cache lines will not be written back to
* memory. Make sure to call functionalWriteback() first if you
* want the to write them to memory.
*/
virtual void memInvalidate() override;
/**
* Determine if there are any dirty blocks in the cache.
*
* @return true if at least one block is dirty, false otherwise.
*/
bool isDirty() const;
/**
* Determine if an address is in the ranges covered by this
* cache. This is useful to filter snoops.
*
* @param addr Address to check against
*
* @return If the address in question is in range
*/
bool inRange(Addr addr) const;
/**
* Find next request ready time from among possible sources.
*/
Tick nextQueueReadyTime() const;
/** Block size of this cache */
const unsigned blkSize;
/**
* The latency of tag lookup of a cache. It occurs when there is
* an access to the cache.
*/
const Cycles lookupLatency;
/**
* The latency of data access of a cache. It occurs when there is
* an access to the cache.
*/
const Cycles dataLatency;
/**
* This is the forward latency of the cache. It occurs when there
* is a cache miss and a request is forwarded downstream, in
* particular an outbound miss.
*/
const Cycles forwardLatency;
/** The latency to fill a cache block */
const Cycles fillLatency;
/**
* The latency of sending reponse to its upper level cache/core on
* a linefill. The responseLatency parameter captures this
* latency.
*/
const Cycles responseLatency;
/**
* Whether tags and data are accessed sequentially.
*/
const bool sequentialAccess;
/** The number of targets for each MSHR. */
const int numTarget;
/** Do we forward snoops from mem side port through to cpu side port? */
bool forwardSnoops;
/**
* Clusivity with respect to the upstream cache, determining if we
* fill into both this cache and the cache above on a miss. Note
* that we currently do not support strict clusivity policies.
*/
const enums::Clusivity clusivity;
/**
* Is this cache read only, for example the instruction cache, or
* table-walker cache. A cache that is read only should never see
* any writes, and should never get any dirty data (and hence
* never have to do any writebacks).
*/
const bool isReadOnly;
/**
* when a data expansion of a compressed block happens it will not be
* able to co-allocate where it is at anymore. If true, the replacement
* policy is called to chose a new location for the block. Otherwise,
* all co-allocated blocks are evicted.
*/
const bool replaceExpansions;
/**
* Similar to data expansions, after a block improves its compression,
* it may need to be moved elsewhere compatible with the new compression
* factor, or, if not required by the compaction method, it may be moved
* to co-allocate with an existing block and thus free an entry.
*/
const bool moveContractions;
/**
* Bit vector of the blocking reasons for the access path.
* @sa #BlockedCause
*/
uint8_t blocked;
/** Increasing order number assigned to each incoming request. */
uint64_t order;
/** Stores time the cache blocked for statistics. */
Cycles blockedCycle;
/** Pointer to the MSHR that has no targets. */
MSHR *noTargetMSHR;
/** The number of misses to trigger an exit event. */
Counter missCount;
/**
* The address range to which the cache responds on the CPU side.
* Normally this is all possible memory addresses. */
const AddrRangeList addrRanges;
public:
/** System we are currently operating in. */
System *system;
struct CacheCmdStats : public statistics::Group
{
CacheCmdStats(BaseCache &c, const std::string &name);
/**
* Callback to register stats from parent
* CacheStats::regStats(). We can't use the normal flow since
* there is is no guaranteed order and CacheStats::regStats()
* needs to rely on these stats being initialised.
*/
void regStatsFromParent();
const BaseCache &cache;
/** Number of hits per thread for each type of command.
@sa Packet::Command */
statistics::Vector hits;
/** Number of misses per thread for each type of command.
@sa Packet::Command */
statistics::Vector misses;
/**
* Total number of ticks per thread/command spent waiting for a hit.
* Used to calculate the average hit latency.
*/
statistics::Vector hitLatency;
/**
* Total number of ticks per thread/command spent waiting for a miss.
* Used to calculate the average miss latency.
*/
statistics::Vector missLatency;
/** The number of accesses per command and thread. */
statistics::Formula accesses;
/** The miss rate per command and thread. */
statistics::Formula missRate;
/** The average miss latency per command and thread. */
statistics::Formula avgMissLatency;
/** Number of misses that hit in the MSHRs per command and thread. */
statistics::Vector mshrHits;
/** Number of misses that miss in the MSHRs, per command and thread. */
statistics::Vector mshrMisses;
/** Number of misses that miss in the MSHRs, per command and thread. */
statistics::Vector mshrUncacheable;
/** Total tick latency of each MSHR miss, per command and thread. */
statistics::Vector mshrMissLatency;
/** Total tick latency of each MSHR miss, per command and thread. */
statistics::Vector mshrUncacheableLatency;
/** The miss rate in the MSHRs pre command and thread. */
statistics::Formula mshrMissRate;
/** The average latency of an MSHR miss, per command and thread. */
statistics::Formula avgMshrMissLatency;
/** The average latency of an MSHR miss, per command and thread. */
statistics::Formula avgMshrUncacheableLatency;
};
struct CacheStats : public statistics::Group
{
CacheStats(BaseCache &c);
void regStats() override;
CacheCmdStats &cmdStats(const PacketPtr p) {
return *cmd[p->cmdToIndex()];
}
const BaseCache &cache;
/** Number of hits for demand accesses. */
statistics::Formula demandHits;
/** Number of hit for all accesses. */
statistics::Formula overallHits;
/** Total number of ticks spent waiting for demand hits. */
statistics::Formula demandHitLatency;
/** Total number of ticks spent waiting for all hits. */
statistics::Formula overallHitLatency;
/** Number of misses for demand accesses. */
statistics::Formula demandMisses;
/** Number of misses for all accesses. */
statistics::Formula overallMisses;
/** Total number of ticks spent waiting for demand misses. */
statistics::Formula demandMissLatency;
/** Total number of ticks spent waiting for all misses. */
statistics::Formula overallMissLatency;
/** The number of demand accesses. */
statistics::Formula demandAccesses;
/** The number of overall accesses. */
statistics::Formula overallAccesses;
/** The miss rate of all demand accesses. */
statistics::Formula demandMissRate;
/** The miss rate for all accesses. */
statistics::Formula overallMissRate;
/** The average miss latency for demand misses. */
statistics::Formula demandAvgMissLatency;
/** The average miss latency for all misses. */
statistics::Formula overallAvgMissLatency;
/** The total number of cycles blocked for each blocked cause. */
statistics::Vector blockedCycles;
/** The number of times this cache blocked for each blocked cause. */
statistics::Vector blockedCauses;
/** The average number of cycles blocked for each blocked cause. */
statistics::Formula avgBlocked;
/** Number of blocks written back per thread. */
statistics::Vector writebacks;
/** Demand misses that hit in the MSHRs. */
statistics::Formula demandMshrHits;
/** Total number of misses that hit in the MSHRs. */
statistics::Formula overallMshrHits;
/** Demand misses that miss in the MSHRs. */
statistics::Formula demandMshrMisses;
/** Total number of misses that miss in the MSHRs. */
statistics::Formula overallMshrMisses;
/** Total number of misses that miss in the MSHRs. */
statistics::Formula overallMshrUncacheable;
/** Total tick latency of demand MSHR misses. */
statistics::Formula demandMshrMissLatency;
/** Total tick latency of overall MSHR misses. */
statistics::Formula overallMshrMissLatency;
/** Total tick latency of overall MSHR misses. */
statistics::Formula overallMshrUncacheableLatency;
/** The demand miss rate in the MSHRs. */
statistics::Formula demandMshrMissRate;
/** The overall miss rate in the MSHRs. */
statistics::Formula overallMshrMissRate;
/** The average latency of a demand MSHR miss. */
statistics::Formula demandAvgMshrMissLatency;
/** The average overall latency of an MSHR miss. */
statistics::Formula overallAvgMshrMissLatency;
/** The average overall latency of an MSHR miss. */
statistics::Formula overallAvgMshrUncacheableLatency;
/** Number of replacements of valid blocks. */
statistics::Scalar replacements;
/** Number of data expansions. */
statistics::Scalar dataExpansions;
/**
* Number of data contractions (blocks that had their compression
* factor improved).
*/
statistics::Scalar dataContractions;
/** Per-command statistics */
std::vector<std::unique_ptr<CacheCmdStats>> cmd;
} stats;
/** Registers probes. */
void regProbePoints() override;
public:
BaseCache(const BaseCacheParams &p, unsigned blk_size);
~BaseCache();
void init() override;
Port &getPort(const std::string &if_name,
PortID idx=InvalidPortID) override;
/**
* Query block size of a cache.
* @return The block size
*/
unsigned
getBlockSize() const
{
return blkSize;
}
const AddrRangeList &getAddrRanges() const { return addrRanges; }
MSHR *allocateMissBuffer(PacketPtr pkt, Tick time, bool sched_send = true)
{
MSHR *mshr = mshrQueue.allocate(pkt->getBlockAddr(blkSize), blkSize,
pkt, time, order++,
allocOnFill(pkt->cmd));
if (mshrQueue.isFull()) {
setBlocked((BlockedCause)MSHRQueue_MSHRs);
}
if (sched_send) {
// schedule the send
schedMemSideSendEvent(time);
}
return mshr;
}
void allocateWriteBuffer(PacketPtr pkt, Tick time)
{
// should only see writes or clean evicts here
assert(pkt->isWrite() || pkt->cmd == MemCmd::CleanEvict);
Addr blk_addr = pkt->getBlockAddr(blkSize);
// If using compression, on evictions the block is decompressed and
// the operation's latency is added to the payload delay. Consume
// that payload delay here, meaning that the data is always stored
// uncompressed in the writebuffer
if (compressor) {
time += pkt->payloadDelay;
pkt->payloadDelay = 0;
}
WriteQueueEntry *wq_entry =
writeBuffer.findMatch(blk_addr, pkt->isSecure());
if (wq_entry && !wq_entry->inService) {
DPRINTF(Cache, "Potential to merge writeback %s", pkt->print());
}
writeBuffer.allocate(blk_addr, blkSize, pkt, time, order++);
if (writeBuffer.isFull()) {
setBlocked((BlockedCause)MSHRQueue_WriteBuffer);
}
// schedule the send
schedMemSideSendEvent(time);
}
/**
* Returns true if the cache is blocked for accesses.
*/
bool isBlocked() const
{
return blocked != 0;
}
/**
* Marks the access path of the cache as blocked for the given cause. This
* also sets the blocked flag in the response interface.
* @param cause The reason for the cache blocking.
*/
void setBlocked(BlockedCause cause)
{
uint8_t flag = 1 << cause;
if (blocked == 0) {
stats.blockedCauses[cause]++;
blockedCycle = curCycle();
cpuSidePort.setBlocked();
}
blocked |= flag;
DPRINTF(Cache,"Blocking for cause %d, mask=%d\n", cause, blocked);
}
/**
* Marks the cache as unblocked for the given cause. This also clears the
* blocked flags in the appropriate interfaces.
* @param cause The newly unblocked cause.
* @warning Calling this function can cause a blocked request on the bus to
* access the cache. The cache must be in a state to handle that request.
*/
void clearBlocked(BlockedCause cause)
{
uint8_t flag = 1 << cause;
blocked &= ~flag;
DPRINTF(Cache,"Unblocking for cause %d, mask=%d\n", cause, blocked);
if (blocked == 0) {
stats.blockedCycles[cause] += curCycle() - blockedCycle;
cpuSidePort.clearBlocked();
}
}
/**
* Schedule a send event for the memory-side port. If already
* scheduled, this may reschedule the event at an earlier
* time. When the specified time is reached, the port is free to
* send either a response, a request, or a prefetch request.
*
* @param time The time when to attempt sending a packet.
*/
void schedMemSideSendEvent(Tick time)
{
memSidePort.schedSendEvent(time);
}
bool inCache(Addr addr, bool is_secure) const {
return tags->findBlock(addr, is_secure);
}
bool hasBeenPrefetched(Addr addr, bool is_secure) const {
CacheBlk *block = tags->findBlock(addr, is_secure);
if (block) {
return block->wasPrefetched();
} else {
return false;
}
}
bool inMissQueue(Addr addr, bool is_secure) const {
return mshrQueue.findMatch(addr, is_secure);
}
void incMissCount(PacketPtr pkt)
{
assert(pkt->req->requestorId() < system->maxRequestors());
stats.cmdStats(pkt).misses[pkt->req->requestorId()]++;
pkt->req->incAccessDepth();
if (missCount) {
--missCount;
if (missCount == 0)
exitSimLoop("A cache reached the maximum miss count");
}
}
void incHitCount(PacketPtr pkt)
{
assert(pkt->req->requestorId() < system->maxRequestors());
stats.cmdStats(pkt).hits[pkt->req->requestorId()]++;
}
/**
* Checks if the cache is coalescing writes
*
* @return True if the cache is coalescing writes
*/
bool coalesce() const;
/**
* Cache block visitor that writes back dirty cache blocks using
* functional writes.
*/
void writebackVisitor(CacheBlk &blk);
/**
* Cache block visitor that invalidates all blocks in the cache.
*
* @warn Dirty cache lines will not be written back to memory.
*/
void invalidateVisitor(CacheBlk &blk);
/**
* Take an MSHR, turn it into a suitable downstream packet, and
* send it out. This construct allows a queue entry to choose a suitable
* approach based on its type.
*
* @param mshr The MSHR to turn into a packet and send
* @return True if the port is waiting for a retry
*/
virtual bool sendMSHRQueuePacket(MSHR* mshr);
/**
* Similar to sendMSHR, but for a write-queue entry
* instead. Create the packet, and send it, and if successful also
* mark the entry in service.
*
* @param wq_entry The write-queue entry to turn into a packet and send
* @return True if the port is waiting for a retry
*/
bool sendWriteQueuePacket(WriteQueueEntry* wq_entry);
/**
* Serialize the state of the caches
*
* We currently don't support checkpointing cache state, so this panics.
*/
void serialize(CheckpointOut &cp) const override;
void unserialize(CheckpointIn &cp) override;
};
/**
* The write allocator inspects write packets and detects streaming
* patterns. The write allocator supports a single stream where writes
* are expected to access consecutive locations and keeps track of
* size of the area covered by the concecutive writes in byteCount.
*
* 1) When byteCount has surpassed the coallesceLimit the mode
* switches from ALLOCATE to COALESCE where writes should be delayed
* until the whole block is written at which point a single packet
* (whole line write) can service them.
*
* 2) When byteCount has also exceeded the noAllocateLimit (whole
* line) we switch to NO_ALLOCATE when writes should not allocate in
* the cache but rather send a whole line write to the memory below.
*/
class WriteAllocator : public SimObject
{
public:
WriteAllocator(const WriteAllocatorParams &p) :
SimObject(p),
coalesceLimit(p.coalesce_limit * p.block_size),
noAllocateLimit(p.no_allocate_limit * p.block_size),
delayThreshold(p.delay_threshold)
{
reset();
}
/**
* Should writes be coalesced? This is true if the mode is set to
* NO_ALLOCATE.
*
* @return return true if the cache should coalesce writes.
*/
bool coalesce() const {
return mode != WriteMode::ALLOCATE;
}
/**
* Should writes allocate?
*
* @return return true if the cache should not allocate for writes.
*/
bool allocate() const {
return mode != WriteMode::NO_ALLOCATE;
}
/**
* Reset the write allocator state, meaning that it allocates for
* writes and has not recorded any information about qualifying
* writes that might trigger a switch to coalescing and later no
* allocation.
*/
void reset() {
mode = WriteMode::ALLOCATE;
byteCount = 0;
nextAddr = 0;
}
/**
* Access whether we need to delay the current write.
*
* @param blk_addr The block address the packet writes to
* @return true if the current packet should be delayed
*/
bool delay(Addr blk_addr) {
if (delayCtr[blk_addr] > 0) {
--delayCtr[blk_addr];
return true;
} else {
return false;
}
}
/**
* Clear delay counter for the input block
*
* @param blk_addr The accessed cache block
*/
void resetDelay(Addr blk_addr) {
delayCtr.erase(blk_addr);
}
/**
* Update the write mode based on the current write
* packet. This method compares the packet's address with any
* current stream, and updates the tracking and the mode
* accordingly.
*
* @param write_addr Start address of the write request
* @param write_size Size of the write request
* @param blk_addr The block address that this packet writes to
*/
void updateMode(Addr write_addr, unsigned write_size, Addr blk_addr);
private:
/**
* The current mode for write coalescing and allocation, either
* normal operation (ALLOCATE), write coalescing (COALESCE), or
* write coalescing without allocation (NO_ALLOCATE).
*/
enum class WriteMode : char
{
ALLOCATE,
COALESCE,
NO_ALLOCATE,
};
WriteMode mode;
/** Address to match writes against to detect streams. */
Addr nextAddr;
/**
* Bytes written contiguously. Saturating once we no longer
* allocate.
*/
uint32_t byteCount;
/**
* Limits for when to switch between the different write modes.
*/
const uint32_t coalesceLimit;
const uint32_t noAllocateLimit;
/**
* The number of times the allocator will delay an WriteReq MSHR.
*/
const uint32_t delayThreshold;
/**
* Keep track of the number of times the allocator has delayed an
* WriteReq MSHR.
*/
std::unordered_map<Addr, Counter> delayCtr;
};
} // namespace gem5
#endif //__MEM_CACHE_BASE_HH__