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40 * Authors: Erik Hallnor
45 * Miss Status and Handling Register (MSHR) declaration.
48 #ifndef __MEM_CACHE_MSHR_HH__
49 #define __MEM_CACHE_MSHR_HH__
56 #include "base/printable.hh"
57 #include "base/types.hh"
58 #include "mem/cache/queue_entry.hh"
59 #include "mem/packet.hh"
60 #include "sim/core.hh"
65 * Miss Status and handling Register. This class keeps all the information
66 * needed to handle a cache miss including a list of target requests.
67 * @sa \ref gem5MemorySystem "gem5 Memory System"
69 class MSHR : public QueueEntry, public Printable
73 * Consider the queues friends to avoid making everything public.
75 template<typename Entry>
77 friend class MSHRQueue;
81 /** Flag set by downstream caches */
82 bool downstreamPending;
85 * Here we use one flag to track both if:
87 * 1. We are going to become owner or not, i.e., we will get the
88 * block in an ownership state (Owned or Modified) with BlkDirty
89 * set. This determines whether or not we are going to become the
90 * responder and ordering point for future requests that we snoop.
92 * 2. We know that we are going to get a writable block, i.e. we
93 * will get the block in writable state (Exclusive or Modified
94 * state) with BlkWritable set. That determines whether additional
95 * targets with needsWritable set will be able to be satisfied, or
96 * if not should be put on the deferred list to possibly wait for
97 * another request that does give us writable access.
99 * Condition 2 is actually just a shortcut that saves us from
100 * possibly building a deferred target list and calling
101 * promoteWritable() every time we get a writable block. Condition
102 * 1, tracking ownership, is what is important. However, we never
103 * receive ownership without marking the block dirty, and
104 * consequently use pendingModified to track both ownership and
105 * writability rather than having separate pendingDirty and
106 * pendingWritable flags.
108 bool pendingModified;
110 /** Did we snoop an invalidate while waiting for data? */
113 /** Did we snoop a read while waiting for data? */
118 /** True if the entry is just a simple forward from an upper level */
130 const Tick recvTime; //!< Time when request was received (for stats)
131 const Tick readyTime; //!< Time when request is ready to be serviced
132 const Counter order; //!< Global order (for memory consistency mgmt)
133 const PacketPtr pkt; //!< Pending request packet.
134 const Source source; //!< Request from cpu, memory, or prefetcher?
137 * We use this flag to track whether we have cleared the
138 * downstreamPending flag for the MSHR of the cache above
139 * where this packet originates from and guard noninitial
140 * attempts to clear it.
142 * The flag markedPending needs to be updated when the
143 * TargetList is in service which can be:
144 * 1) during the Target instantiation if the MSHR is in
145 * service and the target is not deferred,
146 * 2) when the MSHR becomes in service if the target is not
148 * 3) or when the TargetList is promoted (deferredTargets ->
153 const bool allocOnFill; //!< Should the response servicing this
154 //!< target list allocate in the cache?
156 Target(PacketPtr _pkt, Tick _readyTime, Counter _order,
157 Source _source, bool _markedPending, bool alloc_on_fill)
158 : recvTime(curTick()), readyTime(_readyTime), order(_order),
159 pkt(_pkt), source(_source), markedPending(_markedPending),
160 allocOnFill(alloc_on_fill)
164 class TargetList : public std::list<Target> {
169 /** Set when the response should allocate on fill */
172 * Determine whether there was at least one non-snooping
173 * target coming from another cache.
180 * Use the provided packet and the source to update the
181 * flags of this TargetList.
183 * @param pkt Packet considered for the flag update
184 * @param source Indicates the source of the packet
185 * @param alloc_on_fill Whether the pkt would allocate on a fill
187 void updateFlags(PacketPtr pkt, Target::Source source,
191 needsWritable = false;
194 hasFromCache = false;
198 * Goes through the list of targets and uses them to populate
199 * the flags of this TargetList. When the function returns the
200 * flags are consistent with the properties of packets in the
203 void populateFlags();
206 * Tests if the flags of this TargetList have their default
209 bool isReset() const {
210 return !needsWritable && !hasUpgrade && !allocOnFill &&
215 * Add the specified packet in the TargetList. This function
216 * stores information related to the added packet and updates
217 * accordingly the flags.
219 * @param pkt Packet considered for adding
220 * @param readTime Tick at which the packet is processed by this cache
221 * @param order A counter giving a unique id to each target
222 * @param source Indicates the source agent of the packet
223 * @param markPending Set for deferred targets or pending MSHRs
224 * @param alloc_on_fill Whether it should allocate on a fill
226 void add(PacketPtr pkt, Tick readyTime, Counter order,
227 Target::Source source, bool markPending,
231 * Convert upgrades to the equivalent request if the cache line they
232 * refer to would have been invalid (Upgrade -> ReadEx, SC* -> Fail).
233 * Used to rejig ordering between targets waiting on an MSHR. */
234 void replaceUpgrades();
236 void clearDownstreamPending();
237 void clearDownstreamPending(iterator begin, iterator end);
238 bool trySatisfyFunctional(PacketPtr pkt);
239 void print(std::ostream &os, int verbosity,
240 const std::string &prefix) const;
243 /** A list of MSHRs. */
244 typedef std::list<MSHR *> List;
245 /** MSHR list iterator. */
246 typedef List::iterator Iterator;
248 /** The pending* and post* flags are only valid if inService is
249 * true. Using the accessor functions lets us detect if these
250 * flags are accessed improperly.
253 /** True if we need to get a writable copy of the block. */
254 bool needsWritable() const { return targets.needsWritable; }
256 bool isCleaning() const {
257 PacketPtr pkt = targets.front().pkt;
258 return pkt->isClean();
261 bool isPendingModified() const {
262 assert(inService); return pendingModified;
265 bool hasPostInvalidate() const {
266 assert(inService); return postInvalidate;
269 bool hasPostDowngrade() const {
270 assert(inService); return postDowngrade;
273 bool sendPacket(BaseCache &cache);
275 bool allocOnFill() const {
276 return targets.allocOnFill;
280 * Determine if there are non-deferred requests from other caches
282 * @return true if any of the targets is from another cache
284 bool hasFromCache() const {
285 return targets.hasFromCache;
290 * Promotes deferred targets that satisfy a predicate
292 * Deferred targets are promoted to the target list if they
293 * satisfy a given condition. The operation stops at the first
294 * deferred target that doesn't satisfy the condition.
296 * @param pred A condition on a Target
298 void promoteIf(const std::function<bool (Target &)>& pred);
301 * Pointer to this MSHR on the ready list.
302 * @sa MissQueue, MSHRQueue::readyList
307 * Pointer to this MSHR on the allocated list.
308 * @sa MissQueue, MSHRQueue::allocatedList
312 /** List of all requests that match the address */
315 TargetList deferredTargets;
320 * Allocate a miss to this MSHR.
321 * @param blk_addr The address of the block.
322 * @param blk_size The number of bytes to request.
323 * @param pkt The original miss.
324 * @param when_ready When should the MSHR be ready to act upon.
325 * @param _order The logical order of this MSHR
326 * @param alloc_on_fill Should the cache allocate a block on fill
328 void allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
329 Tick when_ready, Counter _order, bool alloc_on_fill);
331 void markInService(bool pending_modified_resp);
333 void clearDownstreamPending();
336 * Mark this MSHR as free.
341 * Add a request to the list of targets.
342 * @param target The target.
344 void allocateTarget(PacketPtr target, Tick when, Counter order,
346 bool handleSnoop(PacketPtr target, Counter order);
348 /** A simple constructor. */
352 * Returns the current number of allocated targets.
353 * @return The current number of allocated targets.
355 int getNumTargets() const
356 { return targets.size() + deferredTargets.size(); }
359 * Extracts the subset of the targets that can be serviced given a
360 * received response. This function returns the targets list
361 * unless the response is a ReadRespWithInvalidate. The
362 * ReadRespWithInvalidate is only invalidating response that its
363 * invalidation was not expected when the request (a
364 * ReadSharedReq) was sent out. For ReadRespWithInvalidate we can
365 * safely service only the first FromCPU target and all FromSnoop
366 * targets (inform all snoopers that we no longer have the block).
368 * @param pkt The response from the downstream memory
370 TargetList extractServiceableTargets(PacketPtr pkt);
373 * Returns true if there are targets left.
374 * @return true if there are targets
376 bool hasTargets() const { return !targets.empty(); }
379 * Returns a reference to the first target.
380 * @return A pointer to the first target.
384 assert(hasTargets());
385 return &targets.front();
396 bool promoteDeferredTargets();
399 * Promotes deferred targets that do not require writable
401 * Move targets from the deferred targets list to the target list
402 * starting from the first deferred target until the first target
403 * that is a cache maintenance operation or needs a writable copy
406 void promoteReadable();
409 * Promotes deferred targets that do not require writable
411 * Requests in the deferred target list are moved to the target
412 * list up until the first target that is a cache maintenance
413 * operation or needs a writable copy of the block
415 void promoteWritable();
417 bool trySatisfyFunctional(PacketPtr pkt);
420 * Prints the contents of this MSHR for debugging.
422 void print(std::ostream &os,
424 const std::string &prefix = "") const;
426 * A no-args wrapper of print(std::ostream...) meant to be
427 * invoked from DPRINTFs avoiding string overheads in fast mode
429 * @return string with mshr fields + [deferred]targets
431 std::string print() const;
434 #endif // __MEM_CACHE_MSHR_HH__