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14 * Copyright (c) 2002-2005 The Regents of The University of Michigan
15 * Copyright (c) 2010 Advanced Micro Devices, Inc.
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19 * modification, are permitted provided that the following conditions are
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29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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31 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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34 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
35 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
36 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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39 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
41 * Authors: Erik Hallnor
48 * Miss Status and Handling Register (MSHR) definitions.
51 #include "mem/cache/mshr.hh"
56 #include "base/logging.hh"
57 #include "base/trace.hh"
58 #include "base/types.hh"
59 #include "debug/Cache.hh"
60 #include "mem/cache/base.hh"
61 #include "mem/request.hh"
62 #include "sim/core.hh"
64 MSHR::MSHR() : downstreamPending(false),
65 pendingModified(false),
66 postInvalidate(false), postDowngrade(false),
67 wasWholeLineWrite(false), isForward(false)
71 MSHR::TargetList::TargetList()
72 : needsWritable(false), hasUpgrade(false), allocOnFill(false),
78 MSHR::TargetList::updateFlags(PacketPtr pkt
, Target::Source source
,
81 if (source
!= Target::FromSnoop
) {
82 if (pkt
->needsWritable()) {
86 // StoreCondReq is effectively an upgrade if it's in an MSHR
87 // since it would have been failed already if we didn't have a
89 if (pkt
->isUpgrade() || pkt
->cmd
== MemCmd::StoreCondReq
) {
93 // potentially re-evaluate whether we should allocate on a fill or
95 allocOnFill
= allocOnFill
|| alloc_on_fill
;
97 if (source
!= Target::FromPrefetcher
) {
98 hasFromCache
= hasFromCache
|| pkt
->fromCache();
100 updateWriteFlags(pkt
);
106 MSHR::TargetList::populateFlags()
109 for (auto& t
: *this) {
110 updateFlags(t
.pkt
, t
.source
, t
.allocOnFill
);
115 MSHR::TargetList::add(PacketPtr pkt
, Tick readyTime
,
116 Counter order
, Target::Source source
, bool markPending
,
119 updateFlags(pkt
, source
, alloc_on_fill
);
121 // Iterate over the SenderState stack and see if we find
122 // an MSHR entry. If we do, set the downstreamPending
123 // flag. Otherwise, do nothing.
124 MSHR
*mshr
= pkt
->findNextSenderState
<MSHR
>();
125 if (mshr
!= nullptr) {
126 assert(!mshr
->downstreamPending
);
127 mshr
->downstreamPending
= true;
129 // No need to clear downstreamPending later
134 emplace_back(pkt
, readyTime
, order
, source
, markPending
, alloc_on_fill
);
139 replaceUpgrade(PacketPtr pkt
)
141 // remember if the current packet has data allocated
142 bool has_data
= pkt
->hasData() || pkt
->hasRespData();
144 if (pkt
->cmd
== MemCmd::UpgradeReq
) {
145 pkt
->cmd
= MemCmd::ReadExReq
;
146 DPRINTF(Cache
, "Replacing UpgradeReq with ReadExReq\n");
147 } else if (pkt
->cmd
== MemCmd::SCUpgradeReq
) {
148 pkt
->cmd
= MemCmd::SCUpgradeFailReq
;
149 DPRINTF(Cache
, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
150 } else if (pkt
->cmd
== MemCmd::StoreCondReq
) {
151 pkt
->cmd
= MemCmd::StoreCondFailReq
;
152 DPRINTF(Cache
, "Replacing StoreCondReq with StoreCondFailReq\n");
156 // there is no sensible way of setting the data field if the
157 // new command actually would carry data
158 assert(!pkt
->hasData());
160 if (pkt
->hasRespData()) {
161 // we went from a packet that had no data (neither request,
162 // nor response), to one that does, and therefore we need to
163 // actually allocate space for the data payload
171 MSHR::TargetList::replaceUpgrades()
176 for (auto& t
: *this) {
177 replaceUpgrade(t
.pkt
);
185 MSHR::TargetList::clearDownstreamPending(MSHR::TargetList::iterator begin
,
186 MSHR::TargetList::iterator end
)
188 for (auto t
= begin
; t
!= end
; t
++) {
189 if (t
->markedPending
) {
190 // Iterate over the SenderState stack and see if we find
191 // an MSHR entry. If we find one, clear the
192 // downstreamPending flag by calling
193 // clearDownstreamPending(). This recursively clears the
194 // downstreamPending flag in all caches this packet has
196 MSHR
*mshr
= t
->pkt
->findNextSenderState
<MSHR
>();
197 if (mshr
!= nullptr) {
198 mshr
->clearDownstreamPending();
200 t
->markedPending
= false;
206 MSHR::TargetList::clearDownstreamPending()
208 clearDownstreamPending(begin(), end());
213 MSHR::TargetList::trySatisfyFunctional(PacketPtr pkt
)
215 for (auto& t
: *this) {
216 if (pkt
->trySatisfyFunctional(t
.pkt
)) {
226 MSHR::TargetList::print(std::ostream
&os
, int verbosity
,
227 const std::string
&prefix
) const
229 for (auto& t
: *this) {
232 case Target::FromCPU
:
235 case Target::FromSnoop
:
238 case Target::FromPrefetcher
:
239 s
= "FromPrefetcher";
245 ccprintf(os
, "%s%s: ", prefix
, s
);
246 t
.pkt
->print(os
, verbosity
, "");
253 MSHR::allocate(Addr blk_addr
, unsigned blk_size
, PacketPtr target
,
254 Tick when_ready
, Counter _order
, bool alloc_on_fill
)
258 isSecure
= target
->isSecure();
259 readyTime
= when_ready
;
263 wasWholeLineWrite
= false;
264 _isUncacheable
= target
->req
->isUncacheable();
266 downstreamPending
= false;
268 targets
.init(blkAddr
, blkSize
);
269 deferredTargets
.init(blkAddr
, blkSize
);
271 // Don't know of a case where we would allocate a new MSHR for a
272 // snoop (mem-side request), so set source according to request here
273 Target::Source source
= (target
->cmd
== MemCmd::HardPFReq
) ?
274 Target::FromPrefetcher
: Target::FromCPU
;
275 targets
.add(target
, when_ready
, _order
, source
, true, alloc_on_fill
);
277 // All targets must refer to the same block
278 assert(target
->matchBlockAddr(targets
.front().pkt
, blkSize
));
283 MSHR::clearDownstreamPending()
285 assert(downstreamPending
);
286 downstreamPending
= false;
287 // recursively clear flag on any MSHRs we will be forwarding
289 targets
.clearDownstreamPending();
293 MSHR::markInService(bool pending_modified_resp
)
298 pendingModified
= targets
.needsWritable
|| pending_modified_resp
;
299 postInvalidate
= postDowngrade
= false;
301 if (!downstreamPending
) {
302 // let upstream caches know that the request has made it to a
303 // level where it's going to get a response
304 targets
.clearDownstreamPending();
306 // if the line is not considered a whole-line write when sent
307 // downstream, make sure it is also not considered a whole-line
308 // write when receiving the response, and vice versa
309 wasWholeLineWrite
= isWholeLineWrite();
316 assert(targets
.empty());
317 targets
.resetFlags();
318 assert(deferredTargets
.isReset());
323 * Adds a target to an MSHR
326 MSHR::allocateTarget(PacketPtr pkt
, Tick whenReady
, Counter _order
,
329 // assume we'd never issue a prefetch when we've got an
331 assert(pkt
->cmd
!= MemCmd::HardPFReq
);
333 // if there's a request already in service for this MSHR, we will
334 // have to defer the new target until after the response if any of
335 // the following are true:
336 // - there are other targets already deferred
337 // - there's a pending invalidate to be applied after the response
338 // comes back (but before this target is processed)
339 // - the MSHR's first (and only) non-deferred target is a cache
340 // maintenance packet
341 // - the new target is a cache maintenance packet (this is probably
342 // overly conservative but certainly safe)
343 // - this target requires a writable block and either we're not
344 // getting a writable block back or we have already snooped
345 // another read request that will downgrade our writable block
346 // to non-writable (Shared or Owned)
347 PacketPtr tgt_pkt
= targets
.front().pkt
;
348 if (pkt
->req
->isCacheMaintenance() ||
349 tgt_pkt
->req
->isCacheMaintenance() ||
350 !deferredTargets
.empty() ||
352 (hasPostInvalidate() ||
353 (pkt
->needsWritable() &&
354 (!isPendingModified() || hasPostDowngrade() || isForward
))))) {
355 // need to put on deferred list
356 if (inService
&& hasPostInvalidate())
358 deferredTargets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, true,
361 // No request outstanding, or still OK to append to
362 // outstanding request: append to regular target list. Only
363 // mark pending if current request hasn't been issued yet
364 // (isn't in service).
365 targets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, !inService
,
371 MSHR::handleSnoop(PacketPtr pkt
, Counter _order
)
373 DPRINTF(Cache
, "%s for %s\n", __func__
, pkt
->print());
375 // when we snoop packets the needsWritable and isInvalidate flags
376 // should always be the same, however, this assumes that we never
377 // snoop writes as they are currently not marked as invalidations
378 panic_if((pkt
->needsWritable() != pkt
->isInvalidate()) &&
379 !pkt
->req
->isCacheMaintenance(),
380 "%s got snoop %s where needsWritable, "
381 "does not match isInvalidate", name(), pkt
->print());
383 if (!inService
|| (pkt
->isExpressSnoop() && downstreamPending
)) {
384 // Request has not been issued yet, or it's been issued
385 // locally but is buffered unissued at some downstream cache
386 // which is forwarding us this snoop. Either way, the packet
387 // we're snooping logically precedes this MSHR's request, so
388 // the snoop has no impact on the MSHR, but must be processed
389 // in the standard way by the cache. The only exception is
390 // that if we're an L2+ cache buffering an UpgradeReq from a
391 // higher-level cache, and the snoop is invalidating, then our
392 // buffered upgrades must be converted to read exclusives,
393 // since the upper-level cache no longer has a valid copy.
394 // That is, even though the upper-level cache got out on its
395 // local bus first, some other invalidating transaction
396 // reached the global bus before the upgrade did.
397 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
398 targets
.replaceUpgrades();
399 deferredTargets
.replaceUpgrades();
405 // From here on down, the request issued by this MSHR logically
406 // precedes the request we're snooping.
407 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
408 // snooped request still precedes the re-request we'll have to
409 // issue for deferred targets, if any...
410 deferredTargets
.replaceUpgrades();
413 PacketPtr tgt_pkt
= targets
.front().pkt
;
414 if (hasPostInvalidate() || tgt_pkt
->req
->isCacheInvalidate()) {
415 // a prior snoop has already appended an invalidation or a
416 // cache invalidation operation is in progress, so logically
417 // we don't have the block anymore; no need for further
422 if (isPendingModified() || pkt
->isInvalidate()) {
423 // We need to save and replay the packet in two cases:
424 // 1. We're awaiting a writable copy (Modified or Exclusive),
425 // so this MSHR is the orgering point, and we need to respond
426 // after we receive data.
427 // 2. It's an invalidation (e.g., UpgradeReq), and we need
428 // to forward the snoop up the hierarchy after the current
429 // transaction completes.
431 // Start by determining if we will eventually respond or not,
432 // matching the conditions checked in Cache::handleSnoop
433 bool will_respond
= isPendingModified() && pkt
->needsResponse() &&
436 // The packet we are snooping may be deleted by the time we
437 // actually process the target, and we consequently need to
438 // save a copy here. Clear flags and also allocate new data as
439 // the original packet data storage may have been deleted by
440 // the time we get to process this packet. In the cases where
441 // we are not responding after handling the snoop we also need
442 // to create a copy of the request to be on the safe side. In
443 // the latter case the cache is responsible for deleting both
444 // the packet and the request as part of handling the deferred
446 PacketPtr cp_pkt
= will_respond
? new Packet(pkt
, true, true) :
447 new Packet(std::make_shared
<Request
>(*pkt
->req
), pkt
->cmd
,
451 // we are the ordering point, and will consequently
452 // respond, and depending on whether the packet
453 // needsWritable or not we either pass a Shared line or a
455 pkt
->setCacheResponding();
457 // inform the cache hierarchy that this cache had the line
458 // in the Modified state, even if the response is passed
459 // as Shared (and thus non-writable)
460 pkt
->setResponderHadWritable();
462 // in the case of an uncacheable request there is no need
463 // to set the responderHadWritable flag, but since the
464 // recipient does not care there is no harm in doing so
465 } else if (isPendingModified() && pkt
->isClean()) {
466 // this cache doesn't respond to the clean request, a
467 // destination xbar will respond to this request, but to
468 // do so it needs to know if it should wait for the
473 targets
.add(cp_pkt
, curTick(), _order
, Target::FromSnoop
,
474 downstreamPending
&& targets
.needsWritable
, false);
476 if (pkt
->needsWritable() || pkt
->isInvalidate()) {
477 // This transaction will take away our pending copy
478 postInvalidate
= true;
482 if (!pkt
->needsWritable() && !pkt
->req
->isUncacheable()) {
483 // This transaction will get a read-shared copy, downgrading
484 // our copy if we had a writable one
485 postDowngrade
= true;
486 // make sure that any downstream cache does not respond with a
487 // writable (and dirty) copy even if it has one, unless it was
488 // explicitly asked for one
489 pkt
->setHasSharers();
496 MSHR::extractServiceableTargets(PacketPtr pkt
)
498 TargetList ready_targets
;
499 ready_targets
.init(blkAddr
, blkSize
);
500 // If the downstream MSHR got an invalidation request then we only
501 // service the first of the FromCPU targets and any other
502 // non-FromCPU target. This way the remaining FromCPU targets
503 // issue a new request and get a fresh copy of the block and we
504 // avoid memory consistency violations.
505 if (pkt
->cmd
== MemCmd::ReadRespWithInvalidate
) {
506 auto it
= targets
.begin();
507 assert((it
->source
== Target::FromCPU
) ||
508 (it
->source
== Target::FromPrefetcher
));
509 ready_targets
.push_back(*it
);
510 it
= targets
.erase(it
);
511 while (it
!= targets
.end()) {
512 if (it
->source
== Target::FromCPU
) {
515 assert(it
->source
== Target::FromSnoop
);
516 ready_targets
.push_back(*it
);
517 it
= targets
.erase(it
);
520 ready_targets
.populateFlags();
522 std::swap(ready_targets
, targets
);
524 targets
.populateFlags();
526 return ready_targets
;
530 MSHR::promoteDeferredTargets()
532 if (targets
.empty() && deferredTargets
.empty()) {
533 // nothing to promote
537 // the deferred targets can be generally promoted unless they
538 // contain a cache maintenance request
540 // find the first target that is a cache maintenance request
541 auto it
= std::find_if(deferredTargets
.begin(), deferredTargets
.end(),
542 [](MSHR::Target
&t
) {
543 return t
.pkt
->req
->isCacheMaintenance();
545 if (it
== deferredTargets
.begin()) {
546 // if the first deferred target is a cache maintenance packet
547 // then we can promote provided the targets list is empty and
548 // we can service it on its own
549 if (targets
.empty()) {
550 targets
.splice(targets
.end(), deferredTargets
, it
);
553 // if a cache maintenance operation exists, we promote all the
554 // deferred targets that precede it, or all deferred targets
556 targets
.splice(targets
.end(), deferredTargets
,
557 deferredTargets
.begin(), it
);
560 deferredTargets
.populateFlags();
561 targets
.populateFlags();
562 order
= targets
.front().order
;
563 readyTime
= std::max(curTick(), targets
.front().readyTime
);
569 MSHR::promoteIf(const std::function
<bool (Target
&)>& pred
)
571 // if any of the deferred targets were upper-level cache
572 // requests marked downstreamPending, need to clear that
573 assert(!downstreamPending
); // not pending here anymore
575 // find the first target does not satisfy the condition
576 auto last_it
= std::find_if_not(deferredTargets
.begin(),
577 deferredTargets
.end(),
580 // for the prefix of the deferredTargets [begin(), last_it) clear
581 // the downstreamPending flag and move them to the target list
582 deferredTargets
.clearDownstreamPending(deferredTargets
.begin(),
584 targets
.splice(targets
.end(), deferredTargets
,
585 deferredTargets
.begin(), last_it
);
586 // We need to update the flags for the target lists after the
588 deferredTargets
.populateFlags();
592 MSHR::promoteReadable()
594 if (!deferredTargets
.empty() && !hasPostInvalidate()) {
595 // We got a non invalidating response, and we have the block
596 // but we have deferred targets which are waiting and they do
597 // not need writable. This can happen if the original request
598 // was for a cache clean operation and we had a copy of the
599 // block. Since we serviced the cache clean operation and we
600 // have the block, there's no need to defer the targets, so
601 // move them up to the regular target list.
603 auto pred
= [](Target
&t
) {
604 assert(t
.source
== Target::FromCPU
);
605 return !t
.pkt
->req
->isCacheInvalidate() &&
606 !t
.pkt
->needsWritable();
613 MSHR::promoteWritable()
615 if (deferredTargets
.needsWritable
&&
616 !(hasPostInvalidate() || hasPostDowngrade())) {
617 // We got a writable response, but we have deferred targets
618 // which are waiting to request a writable copy (not because
619 // of a pending invalidate). This can happen if the original
620 // request was for a read-only block, but we got a writable
621 // response anyway. Since we got the writable copy there's no
622 // need to defer the targets, so move them up to the regular
624 assert(!targets
.needsWritable
);
625 targets
.needsWritable
= true;
627 auto pred
= [](Target
&t
) {
628 assert(t
.source
== Target::FromCPU
);
629 return !t
.pkt
->req
->isCacheInvalidate();
638 MSHR::trySatisfyFunctional(PacketPtr pkt
)
640 // For printing, we treat the MSHR as a whole as single entity.
641 // For other requests, we iterate over the individual targets
642 // since that's where the actual data lies.
643 if (pkt
->isPrint()) {
644 pkt
->trySatisfyFunctional(this, blkAddr
, isSecure
, blkSize
, nullptr);
647 return (targets
.trySatisfyFunctional(pkt
) ||
648 deferredTargets
.trySatisfyFunctional(pkt
));
653 MSHR::sendPacket(BaseCache
&cache
)
655 return cache
.sendMSHRQueuePacket(this);
659 MSHR::print(std::ostream
&os
, int verbosity
, const std::string
&prefix
) const
661 ccprintf(os
, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s %s\n",
662 prefix
, blkAddr
, blkAddr
+ blkSize
- 1,
663 isSecure
? "s" : "ns",
664 isForward
? "Forward" : "",
665 allocOnFill() ? "AllocOnFill" : "",
666 needsWritable() ? "Wrtbl" : "",
667 _isUncacheable
? "Unc" : "",
668 inService
? "InSvc" : "",
669 downstreamPending
? "DwnPend" : "",
670 postInvalidate
? "PostInv" : "",
671 postDowngrade
? "PostDowngr" : "",
672 hasFromCache() ? "HasFromCache" : "");
674 if (!targets
.empty()) {
675 ccprintf(os
, "%s Targets:\n", prefix
);
676 targets
.print(os
, verbosity
, prefix
+ " ");
678 if (!deferredTargets
.empty()) {
679 ccprintf(os
, "%s Deferred Targets:\n", prefix
);
680 deferredTargets
.print(os
, verbosity
, prefix
+ " ");
687 std::ostringstream str
;
693 MSHR::matchBlockAddr(const Addr addr
, const bool is_secure
) const
695 assert(hasTargets());
696 return (blkAddr
== addr
) && (isSecure
== is_secure
);
700 MSHR::matchBlockAddr(const PacketPtr pkt
) const
702 assert(hasTargets());
703 return pkt
->matchBlockAddr(blkAddr
, isSecure
, blkSize
);
707 MSHR::conflictAddr(const QueueEntry
* entry
) const
709 assert(hasTargets());
710 return entry
->matchBlockAddr(blkAddr
, isSecure
);