2 * Copyright (c) 2012-2013, 2015-2018 ARM Limited
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8 * to a hardware implementation of the functionality of the software
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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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27 * this software without specific prior written permission.
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
32 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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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
37 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
38 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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
);
280 MSHR::clearDownstreamPending()
282 assert(downstreamPending
);
283 downstreamPending
= false;
284 // recursively clear flag on any MSHRs we will be forwarding
286 targets
.clearDownstreamPending();
290 MSHR::markInService(bool pending_modified_resp
)
295 pendingModified
= targets
.needsWritable
|| pending_modified_resp
;
296 postInvalidate
= postDowngrade
= false;
298 if (!downstreamPending
) {
299 // let upstream caches know that the request has made it to a
300 // level where it's going to get a response
301 targets
.clearDownstreamPending();
303 // if the line is not considered a whole-line write when sent
304 // downstream, make sure it is also not considered a whole-line
305 // write when receiving the response, and vice versa
306 wasWholeLineWrite
= isWholeLineWrite();
313 assert(targets
.empty());
314 targets
.resetFlags();
315 assert(deferredTargets
.isReset());
320 * Adds a target to an MSHR
323 MSHR::allocateTarget(PacketPtr pkt
, Tick whenReady
, Counter _order
,
326 // assume we'd never issue a prefetch when we've got an
328 assert(pkt
->cmd
!= MemCmd::HardPFReq
);
330 // if there's a request already in service for this MSHR, we will
331 // have to defer the new target until after the response if any of
332 // the following are true:
333 // - there are other targets already deferred
334 // - there's a pending invalidate to be applied after the response
335 // comes back (but before this target is processed)
336 // - the MSHR's first (and only) non-deferred target is a cache
337 // maintenance packet
338 // - the new target is a cache maintenance packet (this is probably
339 // overly conservative but certainly safe)
340 // - this target requires a writable block and either we're not
341 // getting a writable block back or we have already snooped
342 // another read request that will downgrade our writable block
343 // to non-writable (Shared or Owned)
344 PacketPtr tgt_pkt
= targets
.front().pkt
;
345 if (pkt
->req
->isCacheMaintenance() ||
346 tgt_pkt
->req
->isCacheMaintenance() ||
347 !deferredTargets
.empty() ||
349 (hasPostInvalidate() ||
350 (pkt
->needsWritable() &&
351 (!isPendingModified() || hasPostDowngrade() || isForward
))))) {
352 // need to put on deferred list
353 if (inService
&& hasPostInvalidate())
355 deferredTargets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, true,
358 // No request outstanding, or still OK to append to
359 // outstanding request: append to regular target list. Only
360 // mark pending if current request hasn't been issued yet
361 // (isn't in service).
362 targets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, !inService
,
368 MSHR::handleSnoop(PacketPtr pkt
, Counter _order
)
370 DPRINTF(Cache
, "%s for %s\n", __func__
, pkt
->print());
372 // when we snoop packets the needsWritable and isInvalidate flags
373 // should always be the same, however, this assumes that we never
374 // snoop writes as they are currently not marked as invalidations
375 panic_if((pkt
->needsWritable() != pkt
->isInvalidate()) &&
376 !pkt
->req
->isCacheMaintenance(),
377 "%s got snoop %s where needsWritable, "
378 "does not match isInvalidate", name(), pkt
->print());
380 if (!inService
|| (pkt
->isExpressSnoop() && downstreamPending
)) {
381 // Request has not been issued yet, or it's been issued
382 // locally but is buffered unissued at some downstream cache
383 // which is forwarding us this snoop. Either way, the packet
384 // we're snooping logically precedes this MSHR's request, so
385 // the snoop has no impact on the MSHR, but must be processed
386 // in the standard way by the cache. The only exception is
387 // that if we're an L2+ cache buffering an UpgradeReq from a
388 // higher-level cache, and the snoop is invalidating, then our
389 // buffered upgrades must be converted to read exclusives,
390 // since the upper-level cache no longer has a valid copy.
391 // That is, even though the upper-level cache got out on its
392 // local bus first, some other invalidating transaction
393 // reached the global bus before the upgrade did.
394 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
395 targets
.replaceUpgrades();
396 deferredTargets
.replaceUpgrades();
402 // From here on down, the request issued by this MSHR logically
403 // precedes the request we're snooping.
404 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
405 // snooped request still precedes the re-request we'll have to
406 // issue for deferred targets, if any...
407 deferredTargets
.replaceUpgrades();
410 PacketPtr tgt_pkt
= targets
.front().pkt
;
411 if (hasPostInvalidate() || tgt_pkt
->req
->isCacheInvalidate()) {
412 // a prior snoop has already appended an invalidation or a
413 // cache invalidation operation is in progress, so logically
414 // we don't have the block anymore; no need for further
419 if (isPendingModified() || pkt
->isInvalidate()) {
420 // We need to save and replay the packet in two cases:
421 // 1. We're awaiting a writable copy (Modified or Exclusive),
422 // so this MSHR is the orgering point, and we need to respond
423 // after we receive data.
424 // 2. It's an invalidation (e.g., UpgradeReq), and we need
425 // to forward the snoop up the hierarchy after the current
426 // transaction completes.
428 // Start by determining if we will eventually respond or not,
429 // matching the conditions checked in Cache::handleSnoop
430 bool will_respond
= isPendingModified() && pkt
->needsResponse() &&
433 // The packet we are snooping may be deleted by the time we
434 // actually process the target, and we consequently need to
435 // save a copy here. Clear flags and also allocate new data as
436 // the original packet data storage may have been deleted by
437 // the time we get to process this packet. In the cases where
438 // we are not responding after handling the snoop we also need
439 // to create a copy of the request to be on the safe side. In
440 // the latter case the cache is responsible for deleting both
441 // the packet and the request as part of handling the deferred
443 PacketPtr cp_pkt
= will_respond
? new Packet(pkt
, true, true) :
444 new Packet(std::make_shared
<Request
>(*pkt
->req
), pkt
->cmd
,
448 // we are the ordering point, and will consequently
449 // respond, and depending on whether the packet
450 // needsWritable or not we either pass a Shared line or a
452 pkt
->setCacheResponding();
454 // inform the cache hierarchy that this cache had the line
455 // in the Modified state, even if the response is passed
456 // as Shared (and thus non-writable)
457 pkt
->setResponderHadWritable();
459 // in the case of an uncacheable request there is no need
460 // to set the responderHadWritable flag, but since the
461 // recipient does not care there is no harm in doing so
463 targets
.add(cp_pkt
, curTick(), _order
, Target::FromSnoop
,
464 downstreamPending
&& targets
.needsWritable
, false);
466 if (pkt
->needsWritable() || pkt
->isInvalidate()) {
467 // This transaction will take away our pending copy
468 postInvalidate
= true;
471 if (isPendingModified() && pkt
->isClean()) {
476 if (!pkt
->needsWritable() && !pkt
->req
->isUncacheable()) {
477 // This transaction will get a read-shared copy, downgrading
478 // our copy if we had a writable one
479 postDowngrade
= true;
480 // make sure that any downstream cache does not respond with a
481 // writable (and dirty) copy even if it has one, unless it was
482 // explicitly asked for one
483 pkt
->setHasSharers();
490 MSHR::extractServiceableTargets(PacketPtr pkt
)
492 TargetList ready_targets
;
493 ready_targets
.init(blkAddr
, blkSize
);
494 // If the downstream MSHR got an invalidation request then we only
495 // service the first of the FromCPU targets and any other
496 // non-FromCPU target. This way the remaining FromCPU targets
497 // issue a new request and get a fresh copy of the block and we
498 // avoid memory consistency violations.
499 if (pkt
->cmd
== MemCmd::ReadRespWithInvalidate
) {
500 auto it
= targets
.begin();
501 assert((it
->source
== Target::FromCPU
) ||
502 (it
->source
== Target::FromPrefetcher
));
503 ready_targets
.push_back(*it
);
504 it
= targets
.erase(it
);
505 while (it
!= targets
.end()) {
506 if (it
->source
== Target::FromCPU
) {
509 assert(it
->source
== Target::FromSnoop
);
510 ready_targets
.push_back(*it
);
511 it
= targets
.erase(it
);
514 ready_targets
.populateFlags();
516 std::swap(ready_targets
, targets
);
518 targets
.populateFlags();
520 return ready_targets
;
524 MSHR::promoteDeferredTargets()
526 if (targets
.empty() && deferredTargets
.empty()) {
527 // nothing to promote
531 // the deferred targets can be generally promoted unless they
532 // contain a cache maintenance request
534 // find the first target that is a cache maintenance request
535 auto it
= std::find_if(deferredTargets
.begin(), deferredTargets
.end(),
536 [](MSHR::Target
&t
) {
537 return t
.pkt
->req
->isCacheMaintenance();
539 if (it
== deferredTargets
.begin()) {
540 // if the first deferred target is a cache maintenance packet
541 // then we can promote provided the targets list is empty and
542 // we can service it on its own
543 if (targets
.empty()) {
544 targets
.splice(targets
.end(), deferredTargets
, it
);
547 // if a cache maintenance operation exists, we promote all the
548 // deferred targets that precede it, or all deferred targets
550 targets
.splice(targets
.end(), deferredTargets
,
551 deferredTargets
.begin(), it
);
554 deferredTargets
.populateFlags();
555 targets
.populateFlags();
556 order
= targets
.front().order
;
557 readyTime
= std::max(curTick(), targets
.front().readyTime
);
563 MSHR::promoteIf(const std::function
<bool (Target
&)>& pred
)
565 // if any of the deferred targets were upper-level cache
566 // requests marked downstreamPending, need to clear that
567 assert(!downstreamPending
); // not pending here anymore
569 // find the first target does not satisfy the condition
570 auto last_it
= std::find_if_not(deferredTargets
.begin(),
571 deferredTargets
.end(),
574 // for the prefix of the deferredTargets [begin(), last_it) clear
575 // the downstreamPending flag and move them to the target list
576 deferredTargets
.clearDownstreamPending(deferredTargets
.begin(),
578 targets
.splice(targets
.end(), deferredTargets
,
579 deferredTargets
.begin(), last_it
);
580 // We need to update the flags for the target lists after the
582 deferredTargets
.populateFlags();
586 MSHR::promoteReadable()
588 if (!deferredTargets
.empty() && !hasPostInvalidate()) {
589 // We got a non invalidating response, and we have the block
590 // but we have deferred targets which are waiting and they do
591 // not need writable. This can happen if the original request
592 // was for a cache clean operation and we had a copy of the
593 // block. Since we serviced the cache clean operation and we
594 // have the block, there's no need to defer the targets, so
595 // move them up to the regular target list.
597 auto pred
= [](Target
&t
) {
598 assert(t
.source
== Target::FromCPU
);
599 return !t
.pkt
->req
->isCacheInvalidate() &&
600 !t
.pkt
->needsWritable();
607 MSHR::promoteWritable()
609 if (deferredTargets
.needsWritable
&&
610 !(hasPostInvalidate() || hasPostDowngrade())) {
611 // We got a writable response, but we have deferred targets
612 // which are waiting to request a writable copy (not because
613 // of a pending invalidate). This can happen if the original
614 // request was for a read-only block, but we got a writable
615 // response anyway. Since we got the writable copy there's no
616 // need to defer the targets, so move them up to the regular
618 assert(!targets
.needsWritable
);
619 targets
.needsWritable
= true;
621 auto pred
= [](Target
&t
) {
622 assert(t
.source
== Target::FromCPU
);
623 return !t
.pkt
->req
->isCacheInvalidate();
632 MSHR::trySatisfyFunctional(PacketPtr pkt
)
634 // For printing, we treat the MSHR as a whole as single entity.
635 // For other requests, we iterate over the individual targets
636 // since that's where the actual data lies.
637 if (pkt
->isPrint()) {
638 pkt
->trySatisfyFunctional(this, blkAddr
, isSecure
, blkSize
, nullptr);
641 return (targets
.trySatisfyFunctional(pkt
) ||
642 deferredTargets
.trySatisfyFunctional(pkt
));
647 MSHR::sendPacket(BaseCache
&cache
)
649 return cache
.sendMSHRQueuePacket(this);
653 MSHR::print(std::ostream
&os
, int verbosity
, const std::string
&prefix
) const
655 ccprintf(os
, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s %s\n",
656 prefix
, blkAddr
, blkAddr
+ blkSize
- 1,
657 isSecure
? "s" : "ns",
658 isForward
? "Forward" : "",
659 allocOnFill() ? "AllocOnFill" : "",
660 needsWritable() ? "Wrtbl" : "",
661 _isUncacheable
? "Unc" : "",
662 inService
? "InSvc" : "",
663 downstreamPending
? "DwnPend" : "",
664 postInvalidate
? "PostInv" : "",
665 postDowngrade
? "PostDowngr" : "",
666 hasFromCache() ? "HasFromCache" : "");
668 if (!targets
.empty()) {
669 ccprintf(os
, "%s Targets:\n", prefix
);
670 targets
.print(os
, verbosity
, prefix
+ " ");
672 if (!deferredTargets
.empty()) {
673 ccprintf(os
, "%s Deferred Targets:\n", prefix
);
674 deferredTargets
.print(os
, verbosity
, prefix
+ " ");
681 std::ostringstream str
;