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15 * Copyright (c) 2010 Advanced Micro Devices, Inc.
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44 * Miss Status and Handling Register (MSHR) definitions.
47 #include "mem/cache/mshr.hh"
52 #include "base/logging.hh"
53 #include "base/trace.hh"
54 #include "base/types.hh"
55 #include "debug/Cache.hh"
56 #include "mem/cache/base.hh"
57 #include "mem/request.hh"
58 #include "sim/core.hh"
60 MSHR::MSHR() : downstreamPending(false),
61 pendingModified(false),
62 postInvalidate(false), postDowngrade(false),
63 wasWholeLineWrite(false), isForward(false)
67 MSHR::TargetList::TargetList()
68 : needsWritable(false), hasUpgrade(false), allocOnFill(false),
74 MSHR::TargetList::updateFlags(PacketPtr pkt
, Target::Source source
,
77 if (source
!= Target::FromSnoop
) {
78 if (pkt
->needsWritable()) {
82 // StoreCondReq is effectively an upgrade if it's in an MSHR
83 // since it would have been failed already if we didn't have a
85 if (pkt
->isUpgrade() || pkt
->cmd
== MemCmd::StoreCondReq
) {
89 // potentially re-evaluate whether we should allocate on a fill or
91 allocOnFill
= allocOnFill
|| alloc_on_fill
;
93 if (source
!= Target::FromPrefetcher
) {
94 hasFromCache
= hasFromCache
|| pkt
->fromCache();
96 updateWriteFlags(pkt
);
102 MSHR::TargetList::populateFlags()
105 for (auto& t
: *this) {
106 updateFlags(t
.pkt
, t
.source
, t
.allocOnFill
);
111 MSHR::TargetList::updateWriteFlags(PacketPtr pkt
)
113 if (isWholeLineWrite()) {
114 // if we have already seen writes for the full block
115 // stop here, this might be a full line write followed
116 // by other compatible requests (e.g., reads)
120 if (canMergeWrites
) {
121 if (!pkt
->isWrite()) {
122 // We won't allow further merging if this hasn't
124 canMergeWrites
= false;
128 // Avoid merging requests with special flags (e.g.,
130 const Request::FlagsType no_merge_flags
=
131 Request::UNCACHEABLE
| Request::STRICT_ORDER
|
132 Request::PRIVILEGED
| Request::LLSC
| Request::MEM_SWAP
|
133 Request::MEM_SWAP_COND
| Request::SECURE
;
134 const auto &req_flags
= pkt
->req
->getFlags();
135 bool compat_write
= !req_flags
.isSet(no_merge_flags
);
137 // if this is the first write, it might be a whole
138 // line write and even if we can't merge any
139 // subsequent write requests, we still need to service
140 // it as a whole line write (e.g., SECURE whole line
142 bool first_write
= empty();
143 if (first_write
|| compat_write
) {
144 auto offset
= pkt
->getOffset(blkSize
);
145 auto begin
= writesBitmap
.begin() + offset
;
146 std::fill(begin
, begin
+ pkt
->getSize(), true);
149 // We won't allow further merging if this has been a
151 canMergeWrites
&= compat_write
;
156 MSHR::TargetList::add(PacketPtr pkt
, Tick readyTime
,
157 Counter order
, Target::Source source
, bool markPending
,
160 updateFlags(pkt
, source
, alloc_on_fill
);
162 // Iterate over the SenderState stack and see if we find
163 // an MSHR entry. If we do, set the downstreamPending
164 // flag. Otherwise, do nothing.
165 MSHR
*mshr
= pkt
->findNextSenderState
<MSHR
>();
166 if (mshr
!= nullptr) {
167 assert(!mshr
->downstreamPending
);
168 mshr
->downstreamPending
= true;
170 // No need to clear downstreamPending later
175 emplace_back(pkt
, readyTime
, order
, source
, markPending
, alloc_on_fill
);
180 replaceUpgrade(PacketPtr pkt
)
182 // remember if the current packet has data allocated
183 bool has_data
= pkt
->hasData() || pkt
->hasRespData();
185 if (pkt
->cmd
== MemCmd::UpgradeReq
) {
186 pkt
->cmd
= MemCmd::ReadExReq
;
187 DPRINTF(Cache
, "Replacing UpgradeReq with ReadExReq\n");
188 } else if (pkt
->cmd
== MemCmd::SCUpgradeReq
) {
189 pkt
->cmd
= MemCmd::SCUpgradeFailReq
;
190 DPRINTF(Cache
, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
191 } else if (pkt
->cmd
== MemCmd::StoreCondReq
) {
192 pkt
->cmd
= MemCmd::StoreCondFailReq
;
193 DPRINTF(Cache
, "Replacing StoreCondReq with StoreCondFailReq\n");
197 // there is no sensible way of setting the data field if the
198 // new command actually would carry data
199 assert(!pkt
->hasData());
201 if (pkt
->hasRespData()) {
202 // we went from a packet that had no data (neither request,
203 // nor response), to one that does, and therefore we need to
204 // actually allocate space for the data payload
212 MSHR::TargetList::replaceUpgrades()
217 for (auto& t
: *this) {
218 replaceUpgrade(t
.pkt
);
226 MSHR::TargetList::clearDownstreamPending(MSHR::TargetList::iterator begin
,
227 MSHR::TargetList::iterator end
)
229 for (auto t
= begin
; t
!= end
; t
++) {
230 if (t
->markedPending
) {
231 // Iterate over the SenderState stack and see if we find
232 // an MSHR entry. If we find one, clear the
233 // downstreamPending flag by calling
234 // clearDownstreamPending(). This recursively clears the
235 // downstreamPending flag in all caches this packet has
237 MSHR
*mshr
= t
->pkt
->findNextSenderState
<MSHR
>();
238 if (mshr
!= nullptr) {
239 mshr
->clearDownstreamPending();
241 t
->markedPending
= false;
247 MSHR::TargetList::clearDownstreamPending()
249 clearDownstreamPending(begin(), end());
254 MSHR::TargetList::trySatisfyFunctional(PacketPtr pkt
)
256 for (auto& t
: *this) {
257 if (pkt
->trySatisfyFunctional(t
.pkt
)) {
267 MSHR::TargetList::print(std::ostream
&os
, int verbosity
,
268 const std::string
&prefix
) const
270 for (auto& t
: *this) {
273 case Target::FromCPU
:
276 case Target::FromSnoop
:
279 case Target::FromPrefetcher
:
280 s
= "FromPrefetcher";
286 ccprintf(os
, "%s%s: ", prefix
, s
);
287 t
.pkt
->print(os
, verbosity
, "");
294 MSHR::allocate(Addr blk_addr
, unsigned blk_size
, PacketPtr target
,
295 Tick when_ready
, Counter _order
, bool alloc_on_fill
)
299 isSecure
= target
->isSecure();
300 readyTime
= when_ready
;
304 wasWholeLineWrite
= false;
305 _isUncacheable
= target
->req
->isUncacheable();
307 downstreamPending
= false;
309 targets
.init(blkAddr
, blkSize
);
310 deferredTargets
.init(blkAddr
, blkSize
);
312 // Don't know of a case where we would allocate a new MSHR for a
313 // snoop (mem-side request), so set source according to request here
314 Target::Source source
= (target
->cmd
== MemCmd::HardPFReq
) ?
315 Target::FromPrefetcher
: Target::FromCPU
;
316 targets
.add(target
, when_ready
, _order
, source
, true, alloc_on_fill
);
318 // All targets must refer to the same block
319 assert(target
->matchBlockAddr(targets
.front().pkt
, blkSize
));
324 MSHR::clearDownstreamPending()
326 assert(downstreamPending
);
327 downstreamPending
= false;
328 // recursively clear flag on any MSHRs we will be forwarding
330 targets
.clearDownstreamPending();
334 MSHR::markInService(bool pending_modified_resp
)
339 pendingModified
= targets
.needsWritable
|| pending_modified_resp
;
340 postInvalidate
= postDowngrade
= false;
342 if (!downstreamPending
) {
343 // let upstream caches know that the request has made it to a
344 // level where it's going to get a response
345 targets
.clearDownstreamPending();
347 // if the line is not considered a whole-line write when sent
348 // downstream, make sure it is also not considered a whole-line
349 // write when receiving the response, and vice versa
350 wasWholeLineWrite
= isWholeLineWrite();
357 assert(targets
.empty());
358 targets
.resetFlags();
359 assert(deferredTargets
.isReset());
364 * Adds a target to an MSHR
367 MSHR::allocateTarget(PacketPtr pkt
, Tick whenReady
, Counter _order
,
370 // assume we'd never issue a prefetch when we've got an
372 assert(pkt
->cmd
!= MemCmd::HardPFReq
);
374 // if there's a request already in service for this MSHR, we will
375 // have to defer the new target until after the response if any of
376 // the following are true:
377 // - there are other targets already deferred
378 // - there's a pending invalidate to be applied after the response
379 // comes back (but before this target is processed)
380 // - the MSHR's first (and only) non-deferred target is a cache
381 // maintenance packet
382 // - the new target is a cache maintenance packet (this is probably
383 // overly conservative but certainly safe)
384 // - this target requires a writable block and either we're not
385 // getting a writable block back or we have already snooped
386 // another read request that will downgrade our writable block
387 // to non-writable (Shared or Owned)
388 PacketPtr tgt_pkt
= targets
.front().pkt
;
389 if (pkt
->req
->isCacheMaintenance() ||
390 tgt_pkt
->req
->isCacheMaintenance() ||
391 !deferredTargets
.empty() ||
393 (hasPostInvalidate() ||
394 (pkt
->needsWritable() &&
395 (!isPendingModified() || hasPostDowngrade() || isForward
))))) {
396 // need to put on deferred list
397 if (inService
&& hasPostInvalidate())
399 deferredTargets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, true,
402 // No request outstanding, or still OK to append to
403 // outstanding request: append to regular target list. Only
404 // mark pending if current request hasn't been issued yet
405 // (isn't in service).
406 targets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, !inService
,
412 MSHR::handleSnoop(PacketPtr pkt
, Counter _order
)
414 DPRINTF(Cache
, "%s for %s\n", __func__
, pkt
->print());
416 // when we snoop packets the needsWritable and isInvalidate flags
417 // should always be the same, however, this assumes that we never
418 // snoop writes as they are currently not marked as invalidations
419 panic_if((pkt
->needsWritable() != pkt
->isInvalidate()) &&
420 !pkt
->req
->isCacheMaintenance(),
421 "%s got snoop %s where needsWritable, "
422 "does not match isInvalidate", name(), pkt
->print());
424 if (!inService
|| (pkt
->isExpressSnoop() && downstreamPending
)) {
425 // Request has not been issued yet, or it's been issued
426 // locally but is buffered unissued at some downstream cache
427 // which is forwarding us this snoop. Either way, the packet
428 // we're snooping logically precedes this MSHR's request, so
429 // the snoop has no impact on the MSHR, but must be processed
430 // in the standard way by the cache. The only exception is
431 // that if we're an L2+ cache buffering an UpgradeReq from a
432 // higher-level cache, and the snoop is invalidating, then our
433 // buffered upgrades must be converted to read exclusives,
434 // since the upper-level cache no longer has a valid copy.
435 // That is, even though the upper-level cache got out on its
436 // local bus first, some other invalidating transaction
437 // reached the global bus before the upgrade did.
438 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
439 targets
.replaceUpgrades();
440 deferredTargets
.replaceUpgrades();
446 // From here on down, the request issued by this MSHR logically
447 // precedes the request we're snooping.
448 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
449 // snooped request still precedes the re-request we'll have to
450 // issue for deferred targets, if any...
451 deferredTargets
.replaceUpgrades();
454 PacketPtr tgt_pkt
= targets
.front().pkt
;
455 if (hasPostInvalidate() || tgt_pkt
->req
->isCacheInvalidate()) {
456 // a prior snoop has already appended an invalidation or a
457 // cache invalidation operation is in progress, so logically
458 // we don't have the block anymore; no need for further
463 // Start by determining if we will eventually respond or not,
464 // matching the conditions checked in Cache::handleSnoop
465 const bool will_respond
= isPendingModified() && pkt
->needsResponse() &&
467 if (isPendingModified() || pkt
->isInvalidate()) {
468 // We need to save and replay the packet in two cases:
469 // 1. We're awaiting a writable copy (Modified or Exclusive),
470 // so this MSHR is the orgering point, and we need to respond
471 // after we receive data.
472 // 2. It's an invalidation (e.g., UpgradeReq), and we need
473 // to forward the snoop up the hierarchy after the current
474 // transaction completes.
476 // The packet we are snooping may be deleted by the time we
477 // actually process the target, and we consequently need to
478 // save a copy here. Clear flags and also allocate new data as
479 // the original packet data storage may have been deleted by
480 // the time we get to process this packet. In the cases where
481 // we are not responding after handling the snoop we also need
482 // to create a copy of the request to be on the safe side. In
483 // the latter case the cache is responsible for deleting both
484 // the packet and the request as part of handling the deferred
486 PacketPtr cp_pkt
= will_respond
? new Packet(pkt
, true, true) :
487 new Packet(std::make_shared
<Request
>(*pkt
->req
), pkt
->cmd
,
491 // we are the ordering point, and will consequently
492 // respond, and depending on whether the packet
493 // needsWritable or not we either pass a Shared line or a
495 pkt
->setCacheResponding();
497 // inform the cache hierarchy that this cache had the line
498 // in the Modified state, even if the response is passed
499 // as Shared (and thus non-writable)
500 pkt
->setResponderHadWritable();
502 // in the case of an uncacheable request there is no need
503 // to set the responderHadWritable flag, but since the
504 // recipient does not care there is no harm in doing so
505 } else if (isPendingModified() && pkt
->isClean()) {
506 // this cache doesn't respond to the clean request, a
507 // destination xbar will respond to this request, but to
508 // do so it needs to know if it should wait for the
513 targets
.add(cp_pkt
, curTick(), _order
, Target::FromSnoop
,
514 downstreamPending
&& targets
.needsWritable
, false);
516 if (pkt
->needsWritable() || pkt
->isInvalidate()) {
517 // This transaction will take away our pending copy
518 postInvalidate
= true;
522 if (!pkt
->needsWritable() && !pkt
->req
->isUncacheable()) {
523 // This transaction will get a read-shared copy, downgrading
524 // our copy if we had a writable one
525 postDowngrade
= true;
526 // make sure that any downstream cache does not respond with a
527 // writable (and dirty) copy even if it has one, unless it was
528 // explicitly asked for one
529 pkt
->setHasSharers();
536 MSHR::extractServiceableTargets(PacketPtr pkt
)
538 TargetList ready_targets
;
539 ready_targets
.init(blkAddr
, blkSize
);
540 // If the downstream MSHR got an invalidation request then we only
541 // service the first of the FromCPU targets and any other
542 // non-FromCPU target. This way the remaining FromCPU targets
543 // issue a new request and get a fresh copy of the block and we
544 // avoid memory consistency violations.
545 if (pkt
->cmd
== MemCmd::ReadRespWithInvalidate
) {
546 auto it
= targets
.begin();
547 assert((it
->source
== Target::FromCPU
) ||
548 (it
->source
== Target::FromPrefetcher
));
549 ready_targets
.push_back(*it
);
550 it
= targets
.erase(it
);
551 while (it
!= targets
.end()) {
552 if (it
->source
== Target::FromCPU
) {
555 assert(it
->source
== Target::FromSnoop
);
556 ready_targets
.push_back(*it
);
557 it
= targets
.erase(it
);
560 ready_targets
.populateFlags();
562 std::swap(ready_targets
, targets
);
564 targets
.populateFlags();
566 return ready_targets
;
570 MSHR::promoteDeferredTargets()
572 if (targets
.empty() && deferredTargets
.empty()) {
573 // nothing to promote
577 // the deferred targets can be generally promoted unless they
578 // contain a cache maintenance request
580 // find the first target that is a cache maintenance request
581 auto it
= std::find_if(deferredTargets
.begin(), deferredTargets
.end(),
582 [](MSHR::Target
&t
) {
583 return t
.pkt
->req
->isCacheMaintenance();
585 if (it
== deferredTargets
.begin()) {
586 // if the first deferred target is a cache maintenance packet
587 // then we can promote provided the targets list is empty and
588 // we can service it on its own
589 if (targets
.empty()) {
590 targets
.splice(targets
.end(), deferredTargets
, it
);
593 // if a cache maintenance operation exists, we promote all the
594 // deferred targets that precede it, or all deferred targets
596 targets
.splice(targets
.end(), deferredTargets
,
597 deferredTargets
.begin(), it
);
600 deferredTargets
.populateFlags();
601 targets
.populateFlags();
602 order
= targets
.front().order
;
603 readyTime
= std::max(curTick(), targets
.front().readyTime
);
609 MSHR::promoteIf(const std::function
<bool (Target
&)>& pred
)
611 // if any of the deferred targets were upper-level cache
612 // requests marked downstreamPending, need to clear that
613 assert(!downstreamPending
); // not pending here anymore
615 // find the first target does not satisfy the condition
616 auto last_it
= std::find_if_not(deferredTargets
.begin(),
617 deferredTargets
.end(),
620 // for the prefix of the deferredTargets [begin(), last_it) clear
621 // the downstreamPending flag and move them to the target list
622 deferredTargets
.clearDownstreamPending(deferredTargets
.begin(),
624 targets
.splice(targets
.end(), deferredTargets
,
625 deferredTargets
.begin(), last_it
);
626 // We need to update the flags for the target lists after the
628 deferredTargets
.populateFlags();
632 MSHR::promoteReadable()
634 if (!deferredTargets
.empty() && !hasPostInvalidate()) {
635 // We got a non invalidating response, and we have the block
636 // but we have deferred targets which are waiting and they do
637 // not need writable. This can happen if the original request
638 // was for a cache clean operation and we had a copy of the
639 // block. Since we serviced the cache clean operation and we
640 // have the block, there's no need to defer the targets, so
641 // move them up to the regular target list.
643 auto pred
= [](Target
&t
) {
644 assert(t
.source
== Target::FromCPU
);
645 return !t
.pkt
->req
->isCacheInvalidate() &&
646 !t
.pkt
->needsWritable();
653 MSHR::promoteWritable()
655 PacketPtr def_tgt_pkt
= deferredTargets
.front().pkt
;
656 if (deferredTargets
.needsWritable
&&
657 !(hasPostInvalidate() || hasPostDowngrade()) &&
658 !def_tgt_pkt
->req
->isCacheInvalidate()) {
659 // We got a writable response, but we have deferred targets
660 // which are waiting to request a writable copy (not because
661 // of a pending invalidate). This can happen if the original
662 // request was for a read-only block, but we got a writable
663 // response anyway. Since we got the writable copy there's no
664 // need to defer the targets, so move them up to the regular
666 assert(!targets
.needsWritable
);
667 targets
.needsWritable
= true;
669 auto pred
= [](Target
&t
) {
670 assert(t
.source
== Target::FromCPU
);
671 return !t
.pkt
->req
->isCacheInvalidate();
680 MSHR::trySatisfyFunctional(PacketPtr pkt
)
682 // For printing, we treat the MSHR as a whole as single entity.
683 // For other requests, we iterate over the individual targets
684 // since that's where the actual data lies.
685 if (pkt
->isPrint()) {
686 pkt
->trySatisfyFunctional(this, blkAddr
, isSecure
, blkSize
, nullptr);
689 return (targets
.trySatisfyFunctional(pkt
) ||
690 deferredTargets
.trySatisfyFunctional(pkt
));
695 MSHR::sendPacket(BaseCache
&cache
)
697 return cache
.sendMSHRQueuePacket(this);
701 MSHR::print(std::ostream
&os
, int verbosity
, const std::string
&prefix
) const
703 ccprintf(os
, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s %s\n",
704 prefix
, blkAddr
, blkAddr
+ blkSize
- 1,
705 isSecure
? "s" : "ns",
706 isForward
? "Forward" : "",
707 allocOnFill() ? "AllocOnFill" : "",
708 needsWritable() ? "Wrtbl" : "",
709 _isUncacheable
? "Unc" : "",
710 inService
? "InSvc" : "",
711 downstreamPending
? "DwnPend" : "",
712 postInvalidate
? "PostInv" : "",
713 postDowngrade
? "PostDowngr" : "",
714 hasFromCache() ? "HasFromCache" : "");
716 if (!targets
.empty()) {
717 ccprintf(os
, "%s Targets:\n", prefix
);
718 targets
.print(os
, verbosity
, prefix
+ " ");
720 if (!deferredTargets
.empty()) {
721 ccprintf(os
, "%s Deferred Targets:\n", prefix
);
722 deferredTargets
.print(os
, verbosity
, prefix
+ " ");
729 std::ostringstream str
;
735 MSHR::matchBlockAddr(const Addr addr
, const bool is_secure
) const
737 assert(hasTargets());
738 return (blkAddr
== addr
) && (isSecure
== is_secure
);
742 MSHR::matchBlockAddr(const PacketPtr pkt
) const
744 assert(hasTargets());
745 return pkt
->matchBlockAddr(blkAddr
, isSecure
, blkSize
);
749 MSHR::conflictAddr(const QueueEntry
* entry
) const
751 assert(hasTargets());
752 return entry
->matchBlockAddr(blkAddr
, isSecure
);