f1a9b985e3a84946a85a99043584111d61d227c1
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15 * Copyright (c) 2010 Advanced Micro Devices, Inc.
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41 * Authors: Erik Hallnor
47 * Miss Status and Handling Register (MSHR) definitions.
50 #include "mem/cache/mshr.hh"
57 #include "base/logging.hh"
58 #include "base/types.hh"
59 #include "debug/Cache.hh"
60 #include "mem/cache/cache.hh"
61 #include "sim/core.hh"
65 MSHR::MSHR() : downstreamPending(false),
66 pendingModified(false),
67 postInvalidate(false), postDowngrade(false),
72 MSHR::TargetList::TargetList()
73 : 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
;
100 MSHR::TargetList::populateFlags()
103 for (auto& t
: *this) {
104 updateFlags(t
.pkt
, t
.source
, t
.allocOnFill
);
109 MSHR::TargetList::add(PacketPtr pkt
, Tick readyTime
,
110 Counter order
, Target::Source source
, bool markPending
,
113 updateFlags(pkt
, source
, alloc_on_fill
);
115 // Iterate over the SenderState stack and see if we find
116 // an MSHR entry. If we do, set the downstreamPending
117 // flag. Otherwise, do nothing.
118 MSHR
*mshr
= pkt
->findNextSenderState
<MSHR
>();
119 if (mshr
!= nullptr) {
120 assert(!mshr
->downstreamPending
);
121 mshr
->downstreamPending
= true;
123 // No need to clear downstreamPending later
128 emplace_back(pkt
, readyTime
, order
, source
, markPending
, alloc_on_fill
);
133 replaceUpgrade(PacketPtr pkt
)
135 // remember if the current packet has data allocated
136 bool has_data
= pkt
->hasData() || pkt
->hasRespData();
138 if (pkt
->cmd
== MemCmd::UpgradeReq
) {
139 pkt
->cmd
= MemCmd::ReadExReq
;
140 DPRINTF(Cache
, "Replacing UpgradeReq with ReadExReq\n");
141 } else if (pkt
->cmd
== MemCmd::SCUpgradeReq
) {
142 pkt
->cmd
= MemCmd::SCUpgradeFailReq
;
143 DPRINTF(Cache
, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
144 } else if (pkt
->cmd
== MemCmd::StoreCondReq
) {
145 pkt
->cmd
= MemCmd::StoreCondFailReq
;
146 DPRINTF(Cache
, "Replacing StoreCondReq with StoreCondFailReq\n");
150 // there is no sensible way of setting the data field if the
151 // new command actually would carry data
152 assert(!pkt
->hasData());
154 if (pkt
->hasRespData()) {
155 // we went from a packet that had no data (neither request,
156 // nor response), to one that does, and therefore we need to
157 // actually allocate space for the data payload
165 MSHR::TargetList::replaceUpgrades()
170 for (auto& t
: *this) {
171 replaceUpgrade(t
.pkt
);
179 MSHR::TargetList::clearDownstreamPending()
181 for (auto& t
: *this) {
182 if (t
.markedPending
) {
183 // Iterate over the SenderState stack and see if we find
184 // an MSHR entry. If we find one, clear the
185 // downstreamPending flag by calling
186 // clearDownstreamPending(). This recursively clears the
187 // downstreamPending flag in all caches this packet has
189 MSHR
*mshr
= t
.pkt
->findNextSenderState
<MSHR
>();
190 if (mshr
!= nullptr) {
191 mshr
->clearDownstreamPending();
193 t
.markedPending
= false;
200 MSHR::TargetList::checkFunctional(PacketPtr pkt
)
202 for (auto& t
: *this) {
203 if (pkt
->checkFunctional(t
.pkt
)) {
213 MSHR::TargetList::print(std::ostream
&os
, int verbosity
,
214 const std::string
&prefix
) const
216 for (auto& t
: *this) {
219 case Target::FromCPU
:
222 case Target::FromSnoop
:
225 case Target::FromPrefetcher
:
226 s
= "FromPrefetcher";
232 ccprintf(os
, "%s%s: ", prefix
, s
);
233 t
.pkt
->print(os
, verbosity
, "");
240 MSHR::allocate(Addr blk_addr
, unsigned blk_size
, PacketPtr target
,
241 Tick when_ready
, Counter _order
, bool alloc_on_fill
)
245 isSecure
= target
->isSecure();
246 readyTime
= when_ready
;
250 _isUncacheable
= target
->req
->isUncacheable();
252 downstreamPending
= false;
253 assert(targets
.isReset());
254 // Don't know of a case where we would allocate a new MSHR for a
255 // snoop (mem-side request), so set source according to request here
256 Target::Source source
= (target
->cmd
== MemCmd::HardPFReq
) ?
257 Target::FromPrefetcher
: Target::FromCPU
;
258 targets
.add(target
, when_ready
, _order
, source
, true, alloc_on_fill
);
259 assert(deferredTargets
.isReset());
264 MSHR::clearDownstreamPending()
266 assert(downstreamPending
);
267 downstreamPending
= false;
268 // recursively clear flag on any MSHRs we will be forwarding
270 targets
.clearDownstreamPending();
274 MSHR::markInService(bool pending_modified_resp
)
279 pendingModified
= targets
.needsWritable
|| pending_modified_resp
;
280 postInvalidate
= postDowngrade
= false;
282 if (!downstreamPending
) {
283 // let upstream caches know that the request has made it to a
284 // level where it's going to get a response
285 targets
.clearDownstreamPending();
293 assert(targets
.empty());
294 targets
.resetFlags();
295 assert(deferredTargets
.isReset());
300 * Adds a target to an MSHR
303 MSHR::allocateTarget(PacketPtr pkt
, Tick whenReady
, Counter _order
,
306 // assume we'd never issue a prefetch when we've got an
308 assert(pkt
->cmd
!= MemCmd::HardPFReq
);
310 // uncacheable accesses always allocate a new MSHR, and cacheable
311 // accesses ignore any uncacheable MSHRs, thus we should never
312 // have targets addded if originally allocated uncacheable
313 assert(!_isUncacheable
);
315 // if there's a request already in service for this MSHR, we will
316 // have to defer the new target until after the response if any of
317 // the following are true:
318 // - there are other targets already deferred
319 // - there's a pending invalidate to be applied after the response
320 // comes back (but before this target is processed)
321 // - the MSHR's first (and only) non-deferred target is a cache
322 // maintenance packet
323 // - the new target is a cache maintenance packet (this is probably
324 // overly conservative but certainly safe)
325 // - this target requires a writable block and either we're not
326 // getting a writable block back or we have already snooped
327 // another read request that will downgrade our writable block
328 // to non-writable (Shared or Owned)
329 PacketPtr tgt_pkt
= targets
.front().pkt
;
330 if (pkt
->req
->isCacheMaintenance() ||
331 tgt_pkt
->req
->isCacheMaintenance() ||
332 !deferredTargets
.empty() ||
334 (hasPostInvalidate() ||
335 (pkt
->needsWritable() &&
336 (!isPendingModified() || hasPostDowngrade() || isForward
))))) {
337 // need to put on deferred list
338 if (inService
&& hasPostInvalidate())
340 deferredTargets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, true,
343 // No request outstanding, or still OK to append to
344 // outstanding request: append to regular target list. Only
345 // mark pending if current request hasn't been issued yet
346 // (isn't in service).
347 targets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, !inService
,
353 MSHR::handleSnoop(PacketPtr pkt
, Counter _order
)
355 DPRINTF(Cache
, "%s for %s\n", __func__
, pkt
->print());
357 // when we snoop packets the needsWritable and isInvalidate flags
358 // should always be the same, however, this assumes that we never
359 // snoop writes as they are currently not marked as invalidations
360 panic_if((pkt
->needsWritable() != pkt
->isInvalidate()) &&
361 !pkt
->req
->isCacheMaintenance(),
362 "%s got snoop %s where needsWritable, "
363 "does not match isInvalidate", name(), pkt
->print());
365 if (!inService
|| (pkt
->isExpressSnoop() && downstreamPending
)) {
366 // Request has not been issued yet, or it's been issued
367 // locally but is buffered unissued at some downstream cache
368 // which is forwarding us this snoop. Either way, the packet
369 // we're snooping logically precedes this MSHR's request, so
370 // the snoop has no impact on the MSHR, but must be processed
371 // in the standard way by the cache. The only exception is
372 // that if we're an L2+ cache buffering an UpgradeReq from a
373 // higher-level cache, and the snoop is invalidating, then our
374 // buffered upgrades must be converted to read exclusives,
375 // since the upper-level cache no longer has a valid copy.
376 // That is, even though the upper-level cache got out on its
377 // local bus first, some other invalidating transaction
378 // reached the global bus before the upgrade did.
379 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
380 targets
.replaceUpgrades();
381 deferredTargets
.replaceUpgrades();
387 // From here on down, the request issued by this MSHR logically
388 // precedes the request we're snooping.
389 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
390 // snooped request still precedes the re-request we'll have to
391 // issue for deferred targets, if any...
392 deferredTargets
.replaceUpgrades();
395 PacketPtr tgt_pkt
= targets
.front().pkt
;
396 if (hasPostInvalidate() || tgt_pkt
->req
->isCacheInvalidate()) {
397 // a prior snoop has already appended an invalidation or a
398 // cache invalidation operation is in progress, so logically
399 // we don't have the block anymore; no need for further
404 if (isPendingModified() || pkt
->isInvalidate()) {
405 // We need to save and replay the packet in two cases:
406 // 1. We're awaiting a writable copy (Modified or Exclusive),
407 // so this MSHR is the orgering point, and we need to respond
408 // after we receive data.
409 // 2. It's an invalidation (e.g., UpgradeReq), and we need
410 // to forward the snoop up the hierarchy after the current
411 // transaction completes.
413 // Start by determining if we will eventually respond or not,
414 // matching the conditions checked in Cache::handleSnoop
415 bool will_respond
= isPendingModified() && pkt
->needsResponse() &&
418 // The packet we are snooping may be deleted by the time we
419 // actually process the target, and we consequently need to
420 // save a copy here. Clear flags and also allocate new data as
421 // the original packet data storage may have been deleted by
422 // the time we get to process this packet. In the cases where
423 // we are not responding after handling the snoop we also need
424 // to create a copy of the request to be on the safe side. In
425 // the latter case the cache is responsible for deleting both
426 // the packet and the request as part of handling the deferred
428 PacketPtr cp_pkt
= will_respond
? new Packet(pkt
, true, true) :
429 new Packet(new Request(*pkt
->req
), pkt
->cmd
, blkSize
, pkt
->id
);
432 // we are the ordering point, and will consequently
433 // respond, and depending on whether the packet
434 // needsWritable or not we either pass a Shared line or a
436 pkt
->setCacheResponding();
438 // inform the cache hierarchy that this cache had the line
439 // in the Modified state, even if the response is passed
440 // as Shared (and thus non-writable)
441 pkt
->setResponderHadWritable();
443 // in the case of an uncacheable request there is no need
444 // to set the responderHadWritable flag, but since the
445 // recipient does not care there is no harm in doing so
447 targets
.add(cp_pkt
, curTick(), _order
, Target::FromSnoop
,
448 downstreamPending
&& targets
.needsWritable
, false);
450 if (pkt
->needsWritable() || pkt
->isInvalidate()) {
451 // This transaction will take away our pending copy
452 postInvalidate
= true;
455 if (pkt
->isClean()) {
460 if (!pkt
->needsWritable() && !pkt
->req
->isUncacheable()) {
461 // This transaction will get a read-shared copy, downgrading
462 // our copy if we had a writable one
463 postDowngrade
= true;
464 // make sure that any downstream cache does not respond with a
465 // writable (and dirty) copy even if it has one, unless it was
466 // explicitly asked for one
467 pkt
->setHasSharers();
474 MSHR::extractServiceableTargets(PacketPtr pkt
)
476 TargetList ready_targets
;
477 // If the downstream MSHR got an invalidation request then we only
478 // service the first of the FromCPU targets and any other
479 // non-FromCPU target. This way the remaining FromCPU targets
480 // issue a new request and get a fresh copy of the block and we
481 // avoid memory consistency violations.
482 if (pkt
->cmd
== MemCmd::ReadRespWithInvalidate
) {
483 auto it
= targets
.begin();
484 assert((it
->source
== Target::FromCPU
) ||
485 (it
->source
== Target::FromPrefetcher
));
486 ready_targets
.push_back(*it
);
487 it
= targets
.erase(it
);
488 while (it
!= targets
.end()) {
489 if (it
->source
== Target::FromCPU
) {
492 assert(it
->source
== Target::FromSnoop
);
493 ready_targets
.push_back(*it
);
494 it
= targets
.erase(it
);
497 ready_targets
.populateFlags();
499 std::swap(ready_targets
, targets
);
501 targets
.populateFlags();
503 return ready_targets
;
507 MSHR::promoteDeferredTargets()
509 if (targets
.empty() && deferredTargets
.empty()) {
510 // nothing to promote
514 // the deferred targets can be generally promoted unless they
515 // contain a cache maintenance request
517 // find the first target that is a cache maintenance request
518 auto it
= std::find_if(deferredTargets
.begin(), deferredTargets
.end(),
519 [](MSHR::Target
&t
) {
520 return t
.pkt
->req
->isCacheMaintenance();
522 if (it
== deferredTargets
.begin()) {
523 // if the first deferred target is a cache maintenance packet
524 // then we can promote provided the targets list is empty and
525 // we can service it on its own
526 if (targets
.empty()) {
527 targets
.splice(targets
.end(), deferredTargets
, it
);
530 // if a cache maintenance operation exists, we promote all the
531 // deferred targets that precede it, or all deferred targets
533 targets
.splice(targets
.end(), deferredTargets
,
534 deferredTargets
.begin(), it
);
537 deferredTargets
.populateFlags();
538 targets
.populateFlags();
539 order
= targets
.front().order
;
540 readyTime
= std::max(curTick(), targets
.front().readyTime
);
547 MSHR::promoteWritable()
549 if (deferredTargets
.needsWritable
&&
550 !(hasPostInvalidate() || hasPostDowngrade())) {
551 // We got a writable response, but we have deferred targets
552 // which are waiting to request a writable copy (not because
553 // of a pending invalidate). This can happen if the original
554 // request was for a read-only block, but we got a writable
555 // response anyway. Since we got the writable copy there's no
556 // need to defer the targets, so move them up to the regular
558 assert(!targets
.needsWritable
);
559 targets
.needsWritable
= true;
560 // if any of the deferred targets were upper-level cache
561 // requests marked downstreamPending, need to clear that
562 assert(!downstreamPending
); // not pending here anymore
563 deferredTargets
.clearDownstreamPending();
564 // this clears out deferredTargets too
565 targets
.splice(targets
.end(), deferredTargets
);
566 deferredTargets
.resetFlags();
572 MSHR::checkFunctional(PacketPtr pkt
)
574 // For printing, we treat the MSHR as a whole as single entity.
575 // For other requests, we iterate over the individual targets
576 // since that's where the actual data lies.
577 if (pkt
->isPrint()) {
578 pkt
->checkFunctional(this, blkAddr
, isSecure
, blkSize
, nullptr);
581 return (targets
.checkFunctional(pkt
) ||
582 deferredTargets
.checkFunctional(pkt
));
587 MSHR::sendPacket(Cache
&cache
)
589 return cache
.sendMSHRQueuePacket(this);
593 MSHR::print(std::ostream
&os
, int verbosity
, const std::string
&prefix
) const
595 ccprintf(os
, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
596 prefix
, blkAddr
, blkAddr
+ blkSize
- 1,
597 isSecure
? "s" : "ns",
598 isForward
? "Forward" : "",
599 allocOnFill() ? "AllocOnFill" : "",
600 needsWritable() ? "Wrtbl" : "",
601 _isUncacheable
? "Unc" : "",
602 inService
? "InSvc" : "",
603 downstreamPending
? "DwnPend" : "",
604 postInvalidate
? "PostInv" : "",
605 postDowngrade
? "PostDowngr" : "");
607 if (!targets
.empty()) {
608 ccprintf(os
, "%s Targets:\n", prefix
);
609 targets
.print(os
, verbosity
, prefix
+ " ");
611 if (!deferredTargets
.empty()) {
612 ccprintf(os
, "%s Deferred Targets:\n", prefix
);
613 deferredTargets
.print(os
, verbosity
, prefix
+ " ");