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40 * Authors: Erik Hallnor
46 * Miss Status and Handling Register (MSHR) declaration.
49 #ifndef __MEM_CACHE_MSHR_HH__
50 #define __MEM_CACHE_MSHR_HH__
58 #include "base/printable.hh"
59 #include "base/types.hh"
60 #include "mem/cache/queue_entry.hh"
61 #include "mem/packet.hh"
62 #include "mem/request.hh"
63 #include "sim/core.hh"
68 * Miss Status and handling Register. This class keeps all the information
69 * needed to handle a cache miss including a list of target requests.
70 * @sa \ref gem5MemorySystem "gem5 Memory System"
72 class MSHR : public QueueEntry, public Printable
76 * Consider the queues friends to avoid making everything public.
78 template<typename Entry>
80 friend class MSHRQueue;
84 /** Flag set by downstream caches */
85 bool downstreamPending;
88 * Here we use one flag to track both if:
90 * 1. We are going to become owner or not, i.e., we will get the
91 * block in an ownership state (Owned or Modified) with BlkDirty
92 * set. This determines whether or not we are going to become the
93 * responder and ordering point for future requests that we snoop.
95 * 2. We know that we are going to get a writable block, i.e. we
96 * will get the block in writable state (Exclusive or Modified
97 * state) with BlkWritable set. That determines whether additional
98 * targets with needsWritable set will be able to be satisfied, or
99 * if not should be put on the deferred list to possibly wait for
100 * another request that does give us writable access.
102 * Condition 2 is actually just a shortcut that saves us from
103 * possibly building a deferred target list and calling
104 * promoteWritable() every time we get a writable block. Condition
105 * 1, tracking ownership, is what is important. However, we never
106 * receive ownership without marking the block dirty, and
107 * consequently use pendingModified to track both ownership and
108 * writability rather than having separate pendingDirty and
109 * pendingWritable flags.
111 bool pendingModified;
113 /** Did we snoop an invalidate while waiting for data? */
116 /** Did we snoop a read while waiting for data? */
121 /** Track if we sent this as a whole line write or not */
122 bool wasWholeLineWrite;
124 /** True if the entry is just a simple forward from an upper level */
127 class Target : public QueueEntry::Target {
136 const Source source; //!< Request from cpu, memory, or prefetcher?
139 * We use this flag to track whether we have cleared the
140 * downstreamPending flag for the MSHR of the cache above
141 * where this packet originates from and guard noninitial
142 * attempts to clear it.
144 * The flag markedPending needs to be updated when the
145 * TargetList is in service which can be:
146 * 1) during the Target instantiation if the MSHR is in
147 * service and the target is not deferred,
148 * 2) when the MSHR becomes in service if the target is not
150 * 3) or when the TargetList is promoted (deferredTargets ->
155 const bool allocOnFill; //!< Should the response servicing this
156 //!< target list allocate in the cache?
158 Target(PacketPtr _pkt, Tick _readyTime, Counter _order,
159 Source _source, bool _markedPending, bool alloc_on_fill)
160 : QueueEntry::Target(_pkt, _readyTime, _order), source(_source),
161 markedPending(_markedPending), allocOnFill(alloc_on_fill)
165 class TargetList : public std::list<Target> {
170 /** Set when the response should allocate on fill */
173 * Determine whether there was at least one non-snooping
174 * target coming from another cache.
181 * Use the provided packet and the source to update the
182 * flags of this TargetList.
184 * @param pkt Packet considered for the flag update
185 * @param source Indicates the source of the packet
186 * @param alloc_on_fill Whether the pkt would allocate on a fill
188 void updateFlags(PacketPtr pkt, Target::Source source,
194 * @param blk_addr Address of the cache block
195 * @param blk_size Size of the cache block
197 void init(Addr blk_addr, Addr blk_size) {
200 writesBitmap.resize(blk_size);
207 std::fill(writesBitmap.begin(), writesBitmap.end(), false);
209 needsWritable = false;
212 hasFromCache = false;
216 * Goes through the list of targets and uses them to populate
217 * the flags of this TargetList. When the function returns the
218 * flags are consistent with the properties of packets in the
221 void populateFlags();
224 * Add the specified packet in the TargetList. This function
225 * stores information related to the added packet and updates
226 * accordingly the flags.
228 * @param pkt Packet considered for adding
230 void updateWriteFlags(PacketPtr pkt) {
231 const Request::FlagsType noMergeFlags =
232 Request::UNCACHEABLE |
233 Request::STRICT_ORDER | Request::MMAPPED_IPR |
234 Request::PRIVILEGED | Request::LLSC |
235 Request::MEM_SWAP | Request::MEM_SWAP_COND |
238 // if we have already seen writes for the full block stop
239 // here, this might be a full line write followed by
240 // other compatible requests (e.g., reads)
241 if (!isWholeLineWrite()) {
242 bool can_merge_write = pkt->isWrite() &&
243 ((pkt->req->getFlags() & noMergeFlags) == 0);
244 onlyWrites &= can_merge_write;
246 auto offset = pkt->getOffset(blkSize);
247 auto begin = writesBitmap.begin() + offset;
248 std::fill(begin, begin + pkt->getSize(), true);
254 * Tests if the flags of this TargetList have their default
257 * @return True if the TargetList are reset, false otherwise.
259 bool isReset() const {
260 return !needsWritable && !hasUpgrade && !allocOnFill &&
261 !hasFromCache && onlyWrites;
265 * Add the specified packet in the TargetList. This function
266 * stores information related to the added packet and updates
267 * accordingly the flags.
269 * @param pkt Packet considered for adding
270 * @param readTime Tick at which the packet is processed by this cache
271 * @param order A counter giving a unique id to each target
272 * @param source Indicates the source agent of the packet
273 * @param markPending Set for deferred targets or pending MSHRs
274 * @param alloc_on_fill Whether it should allocate on a fill
276 void add(PacketPtr pkt, Tick readyTime, Counter order,
277 Target::Source source, bool markPending, bool alloc_on_fill);
280 * Convert upgrades to the equivalent request if the cache line they
281 * refer to would have been invalid (Upgrade -> ReadEx, SC* -> Fail).
282 * Used to rejig ordering between targets waiting on an MSHR. */
283 void replaceUpgrades();
285 void clearDownstreamPending();
286 void clearDownstreamPending(iterator begin, iterator end);
287 bool trySatisfyFunctional(PacketPtr pkt);
288 void print(std::ostream &os, int verbosity,
289 const std::string &prefix) const;
292 * Check if this list contains only compatible writes, and if they
293 * span the entire cache line. This is used as part of the
294 * miss-packet creation. Note that new requests may arrive after a
295 * miss-packet has been created, and for the fill we therefore use
296 * the wasWholeLineWrite field.
298 bool isWholeLineWrite() const
301 std::all_of(writesBitmap.begin(),
302 writesBitmap.end(), [](bool i) { return i; });
306 /** Address of the cache block for this list of targets. */
309 /** Size of the cache block. */
312 /** Are we only dealing with writes. */
315 // NOTE: std::vector<bool> might not meet satisfy the
316 // ForwardIterator requirement and therefore cannot be used
319 * Track which bytes are written by requests in this target
322 std::vector<char> writesBitmap;
325 /** A list of MSHRs. */
326 typedef std::list<MSHR *> List;
327 /** MSHR list iterator. */
328 typedef List::iterator Iterator;
330 /** The pending* and post* flags are only valid if inService is
331 * true. Using the accessor functions lets us detect if these
332 * flags are accessed improperly.
335 /** True if we need to get a writable copy of the block. */
336 bool needsWritable() const { return targets.needsWritable; }
338 bool isCleaning() const {
339 PacketPtr pkt = targets.front().pkt;
340 return pkt->isClean();
343 bool isPendingModified() const {
344 assert(inService); return pendingModified;
347 bool hasPostInvalidate() const {
348 assert(inService); return postInvalidate;
351 bool hasPostDowngrade() const {
352 assert(inService); return postDowngrade;
355 bool sendPacket(BaseCache &cache);
357 bool allocOnFill() const {
358 return targets.allocOnFill;
362 * Determine if there are non-deferred requests from other caches
364 * @return true if any of the targets is from another cache
366 bool hasFromCache() const {
367 return targets.hasFromCache;
372 * Promotes deferred targets that satisfy a predicate
374 * Deferred targets are promoted to the target list if they
375 * satisfy a given condition. The operation stops at the first
376 * deferred target that doesn't satisfy the condition.
378 * @param pred A condition on a Target
380 void promoteIf(const std::function<bool (Target &)>& pred);
383 * Pointer to this MSHR on the ready list.
384 * @sa MissQueue, MSHRQueue::readyList
389 * Pointer to this MSHR on the allocated list.
390 * @sa MissQueue, MSHRQueue::allocatedList
394 /** List of all requests that match the address */
397 TargetList deferredTargets;
401 * Check if this MSHR contains only compatible writes, and if they
402 * span the entire cache line. This is used as part of the
403 * miss-packet creation. Note that new requests may arrive after a
404 * miss-packet has been created, and for the fill we therefore use
405 * the wasWholeLineWrite field.
407 bool isWholeLineWrite() const {
408 return targets.isWholeLineWrite();
412 * Allocate a miss to this MSHR.
413 * @param blk_addr The address of the block.
414 * @param blk_size The number of bytes to request.
415 * @param pkt The original miss.
416 * @param when_ready When should the MSHR be ready to act upon.
417 * @param _order The logical order of this MSHR
418 * @param alloc_on_fill Should the cache allocate a block on fill
420 void allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
421 Tick when_ready, Counter _order, bool alloc_on_fill);
423 void markInService(bool pending_modified_resp);
425 void clearDownstreamPending();
428 * Mark this MSHR as free.
433 * Add a request to the list of targets.
434 * @param target The target.
436 void allocateTarget(PacketPtr target, Tick when, Counter order,
438 bool handleSnoop(PacketPtr target, Counter order);
440 /** A simple constructor. */
444 * Returns the current number of allocated targets.
445 * @return The current number of allocated targets.
447 int getNumTargets() const
448 { return targets.size() + deferredTargets.size(); }
451 * Extracts the subset of the targets that can be serviced given a
452 * received response. This function returns the targets list
453 * unless the response is a ReadRespWithInvalidate. The
454 * ReadRespWithInvalidate is only invalidating response that its
455 * invalidation was not expected when the request (a
456 * ReadSharedReq) was sent out. For ReadRespWithInvalidate we can
457 * safely service only the first FromCPU target and all FromSnoop
458 * targets (inform all snoopers that we no longer have the block).
460 * @param pkt The response from the downstream memory
462 TargetList extractServiceableTargets(PacketPtr pkt);
465 * Returns true if there are targets left.
466 * @return true if there are targets
468 bool hasTargets() const { return !targets.empty(); }
471 * Returns a reference to the first target.
472 * @return A pointer to the first target.
474 QueueEntry::Target *getTarget() override
476 assert(hasTargets());
477 return &targets.front();
488 bool promoteDeferredTargets();
491 * Promotes deferred targets that do not require writable
493 * Move targets from the deferred targets list to the target list
494 * starting from the first deferred target until the first target
495 * that is a cache maintenance operation or needs a writable copy
498 void promoteReadable();
501 * Promotes deferred targets that do not require writable
503 * Requests in the deferred target list are moved to the target
504 * list up until the first target that is a cache maintenance
505 * operation or needs a writable copy of the block
507 void promoteWritable();
509 bool trySatisfyFunctional(PacketPtr pkt);
512 * Adds a delay relative to the current tick to the current MSHR
513 * @param delay_ticks the desired delay in ticks
515 void delay(Tick delay_ticks)
517 assert(readyTime <= curTick());
518 readyTime = curTick() + delay_ticks;
522 * Prints the contents of this MSHR for debugging.
524 void print(std::ostream &os,
526 const std::string &prefix = "") const;
528 * A no-args wrapper of print(std::ostream...) meant to be
529 * invoked from DPRINTFs avoiding string overheads in fast mode
531 * @return string with mshr fields + [deferred]targets
533 std::string print() const;
535 bool matchBlockAddr(const Addr addr, const bool is_secure) const override;
536 bool matchBlockAddr(const PacketPtr pkt) const override;
537 bool conflictAddr(const QueueEntry* entry) const override;
540 #endif // __MEM_CACHE_MSHR_HH__