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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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35 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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39 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
41 * Authors: Erik Hallnor
47 * Miss Status and Handling Register (MSHR) definitions.
50 #include "mem/cache/mshr.hh"
55 #include "base/logging.hh"
56 #include "base/trace.hh"
57 #include "base/types.hh"
58 #include "debug/Cache.hh"
59 #include "mem/cache/base.hh"
60 #include "mem/request.hh"
61 #include "sim/core.hh"
63 MSHR::MSHR() : downstreamPending(false),
64 pendingModified(false),
65 postInvalidate(false), postDowngrade(false),
70 MSHR::TargetList::TargetList()
71 : needsWritable(false), hasUpgrade(false), allocOnFill(false),
77 MSHR::TargetList::updateFlags(PacketPtr pkt
, Target::Source source
,
80 if (source
!= Target::FromSnoop
) {
81 if (pkt
->needsWritable()) {
85 // StoreCondReq is effectively an upgrade if it's in an MSHR
86 // since it would have been failed already if we didn't have a
88 if (pkt
->isUpgrade() || pkt
->cmd
== MemCmd::StoreCondReq
) {
92 // potentially re-evaluate whether we should allocate on a fill or
94 allocOnFill
= allocOnFill
|| alloc_on_fill
;
96 if (source
!= Target::FromPrefetcher
) {
97 hasFromCache
= hasFromCache
|| pkt
->fromCache();
103 MSHR::TargetList::populateFlags()
106 for (auto& t
: *this) {
107 updateFlags(t
.pkt
, t
.source
, t
.allocOnFill
);
112 MSHR::TargetList::add(PacketPtr pkt
, Tick readyTime
,
113 Counter order
, Target::Source source
, bool markPending
,
116 updateFlags(pkt
, source
, alloc_on_fill
);
118 // Iterate over the SenderState stack and see if we find
119 // an MSHR entry. If we do, set the downstreamPending
120 // flag. Otherwise, do nothing.
121 MSHR
*mshr
= pkt
->findNextSenderState
<MSHR
>();
122 if (mshr
!= nullptr) {
123 assert(!mshr
->downstreamPending
);
124 mshr
->downstreamPending
= true;
126 // No need to clear downstreamPending later
131 emplace_back(pkt
, readyTime
, order
, source
, markPending
, alloc_on_fill
);
136 replaceUpgrade(PacketPtr pkt
)
138 // remember if the current packet has data allocated
139 bool has_data
= pkt
->hasData() || pkt
->hasRespData();
141 if (pkt
->cmd
== MemCmd::UpgradeReq
) {
142 pkt
->cmd
= MemCmd::ReadExReq
;
143 DPRINTF(Cache
, "Replacing UpgradeReq with ReadExReq\n");
144 } else if (pkt
->cmd
== MemCmd::SCUpgradeReq
) {
145 pkt
->cmd
= MemCmd::SCUpgradeFailReq
;
146 DPRINTF(Cache
, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
147 } else if (pkt
->cmd
== MemCmd::StoreCondReq
) {
148 pkt
->cmd
= MemCmd::StoreCondFailReq
;
149 DPRINTF(Cache
, "Replacing StoreCondReq with StoreCondFailReq\n");
153 // there is no sensible way of setting the data field if the
154 // new command actually would carry data
155 assert(!pkt
->hasData());
157 if (pkt
->hasRespData()) {
158 // we went from a packet that had no data (neither request,
159 // nor response), to one that does, and therefore we need to
160 // actually allocate space for the data payload
168 MSHR::TargetList::replaceUpgrades()
173 for (auto& t
: *this) {
174 replaceUpgrade(t
.pkt
);
182 MSHR::TargetList::clearDownstreamPending()
184 for (auto& t
: *this) {
185 if (t
.markedPending
) {
186 // Iterate over the SenderState stack and see if we find
187 // an MSHR entry. If we find one, clear the
188 // downstreamPending flag by calling
189 // clearDownstreamPending(). This recursively clears the
190 // downstreamPending flag in all caches this packet has
192 MSHR
*mshr
= t
.pkt
->findNextSenderState
<MSHR
>();
193 if (mshr
!= nullptr) {
194 mshr
->clearDownstreamPending();
196 t
.markedPending
= false;
203 MSHR::TargetList::checkFunctional(PacketPtr pkt
)
205 for (auto& t
: *this) {
206 if (pkt
->checkFunctional(t
.pkt
)) {
216 MSHR::TargetList::print(std::ostream
&os
, int verbosity
,
217 const std::string
&prefix
) const
219 for (auto& t
: *this) {
222 case Target::FromCPU
:
225 case Target::FromSnoop
:
228 case Target::FromPrefetcher
:
229 s
= "FromPrefetcher";
235 ccprintf(os
, "%s%s: ", prefix
, s
);
236 t
.pkt
->print(os
, verbosity
, "");
243 MSHR::allocate(Addr blk_addr
, unsigned blk_size
, PacketPtr target
,
244 Tick when_ready
, Counter _order
, bool alloc_on_fill
)
248 isSecure
= target
->isSecure();
249 readyTime
= when_ready
;
253 _isUncacheable
= target
->req
->isUncacheable();
255 downstreamPending
= false;
256 assert(targets
.isReset());
257 // Don't know of a case where we would allocate a new MSHR for a
258 // snoop (mem-side request), so set source according to request here
259 Target::Source source
= (target
->cmd
== MemCmd::HardPFReq
) ?
260 Target::FromPrefetcher
: Target::FromCPU
;
261 targets
.add(target
, when_ready
, _order
, source
, true, alloc_on_fill
);
262 assert(deferredTargets
.isReset());
267 MSHR::clearDownstreamPending()
269 assert(downstreamPending
);
270 downstreamPending
= false;
271 // recursively clear flag on any MSHRs we will be forwarding
273 targets
.clearDownstreamPending();
277 MSHR::markInService(bool pending_modified_resp
)
282 pendingModified
= targets
.needsWritable
|| pending_modified_resp
;
283 postInvalidate
= postDowngrade
= false;
285 if (!downstreamPending
) {
286 // let upstream caches know that the request has made it to a
287 // level where it's going to get a response
288 targets
.clearDownstreamPending();
296 assert(targets
.empty());
297 targets
.resetFlags();
298 assert(deferredTargets
.isReset());
303 * Adds a target to an MSHR
306 MSHR::allocateTarget(PacketPtr pkt
, Tick whenReady
, Counter _order
,
309 // assume we'd never issue a prefetch when we've got an
311 assert(pkt
->cmd
!= MemCmd::HardPFReq
);
313 // if there's a request already in service for this MSHR, we will
314 // have to defer the new target until after the response if any of
315 // the following are true:
316 // - there are other targets already deferred
317 // - there's a pending invalidate to be applied after the response
318 // comes back (but before this target is processed)
319 // - the MSHR's first (and only) non-deferred target is a cache
320 // maintenance packet
321 // - the new target is a cache maintenance packet (this is probably
322 // overly conservative but certainly safe)
323 // - this target requires a writable block and either we're not
324 // getting a writable block back or we have already snooped
325 // another read request that will downgrade our writable block
326 // to non-writable (Shared or Owned)
327 PacketPtr tgt_pkt
= targets
.front().pkt
;
328 if (pkt
->req
->isCacheMaintenance() ||
329 tgt_pkt
->req
->isCacheMaintenance() ||
330 !deferredTargets
.empty() ||
332 (hasPostInvalidate() ||
333 (pkt
->needsWritable() &&
334 (!isPendingModified() || hasPostDowngrade() || isForward
))))) {
335 // need to put on deferred list
336 if (inService
&& hasPostInvalidate())
338 deferredTargets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, true,
341 // No request outstanding, or still OK to append to
342 // outstanding request: append to regular target list. Only
343 // mark pending if current request hasn't been issued yet
344 // (isn't in service).
345 targets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, !inService
,
351 MSHR::handleSnoop(PacketPtr pkt
, Counter _order
)
353 DPRINTF(Cache
, "%s for %s\n", __func__
, pkt
->print());
355 // when we snoop packets the needsWritable and isInvalidate flags
356 // should always be the same, however, this assumes that we never
357 // snoop writes as they are currently not marked as invalidations
358 panic_if((pkt
->needsWritable() != pkt
->isInvalidate()) &&
359 !pkt
->req
->isCacheMaintenance(),
360 "%s got snoop %s where needsWritable, "
361 "does not match isInvalidate", name(), pkt
->print());
363 if (!inService
|| (pkt
->isExpressSnoop() && downstreamPending
)) {
364 // Request has not been issued yet, or it's been issued
365 // locally but is buffered unissued at some downstream cache
366 // which is forwarding us this snoop. Either way, the packet
367 // we're snooping logically precedes this MSHR's request, so
368 // the snoop has no impact on the MSHR, but must be processed
369 // in the standard way by the cache. The only exception is
370 // that if we're an L2+ cache buffering an UpgradeReq from a
371 // higher-level cache, and the snoop is invalidating, then our
372 // buffered upgrades must be converted to read exclusives,
373 // since the upper-level cache no longer has a valid copy.
374 // That is, even though the upper-level cache got out on its
375 // local bus first, some other invalidating transaction
376 // reached the global bus before the upgrade did.
377 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
378 targets
.replaceUpgrades();
379 deferredTargets
.replaceUpgrades();
385 // From here on down, the request issued by this MSHR logically
386 // precedes the request we're snooping.
387 if (pkt
->needsWritable() || pkt
->req
->isCacheInvalidate()) {
388 // snooped request still precedes the re-request we'll have to
389 // issue for deferred targets, if any...
390 deferredTargets
.replaceUpgrades();
393 PacketPtr tgt_pkt
= targets
.front().pkt
;
394 if (hasPostInvalidate() || tgt_pkt
->req
->isCacheInvalidate()) {
395 // a prior snoop has already appended an invalidation or a
396 // cache invalidation operation is in progress, so logically
397 // we don't have the block anymore; no need for further
402 if (isPendingModified() || pkt
->isInvalidate()) {
403 // We need to save and replay the packet in two cases:
404 // 1. We're awaiting a writable copy (Modified or Exclusive),
405 // so this MSHR is the orgering point, and we need to respond
406 // after we receive data.
407 // 2. It's an invalidation (e.g., UpgradeReq), and we need
408 // to forward the snoop up the hierarchy after the current
409 // transaction completes.
411 // Start by determining if we will eventually respond or not,
412 // matching the conditions checked in Cache::handleSnoop
413 bool will_respond
= isPendingModified() && pkt
->needsResponse() &&
416 // The packet we are snooping may be deleted by the time we
417 // actually process the target, and we consequently need to
418 // save a copy here. Clear flags and also allocate new data as
419 // the original packet data storage may have been deleted by
420 // the time we get to process this packet. In the cases where
421 // we are not responding after handling the snoop we also need
422 // to create a copy of the request to be on the safe side. In
423 // the latter case the cache is responsible for deleting both
424 // the packet and the request as part of handling the deferred
426 PacketPtr cp_pkt
= will_respond
? new Packet(pkt
, true, true) :
427 new Packet(new Request(*pkt
->req
), pkt
->cmd
, blkSize
, pkt
->id
);
430 // we are the ordering point, and will consequently
431 // respond, and depending on whether the packet
432 // needsWritable or not we either pass a Shared line or a
434 pkt
->setCacheResponding();
436 // inform the cache hierarchy that this cache had the line
437 // in the Modified state, even if the response is passed
438 // as Shared (and thus non-writable)
439 pkt
->setResponderHadWritable();
441 // in the case of an uncacheable request there is no need
442 // to set the responderHadWritable flag, but since the
443 // recipient does not care there is no harm in doing so
445 targets
.add(cp_pkt
, curTick(), _order
, Target::FromSnoop
,
446 downstreamPending
&& targets
.needsWritable
, false);
448 if (pkt
->needsWritable() || pkt
->isInvalidate()) {
449 // This transaction will take away our pending copy
450 postInvalidate
= true;
453 if (isPendingModified() && pkt
->isClean()) {
458 if (!pkt
->needsWritable() && !pkt
->req
->isUncacheable()) {
459 // This transaction will get a read-shared copy, downgrading
460 // our copy if we had a writable one
461 postDowngrade
= true;
462 // make sure that any downstream cache does not respond with a
463 // writable (and dirty) copy even if it has one, unless it was
464 // explicitly asked for one
465 pkt
->setHasSharers();
472 MSHR::extractServiceableTargets(PacketPtr pkt
)
474 TargetList ready_targets
;
475 // If the downstream MSHR got an invalidation request then we only
476 // service the first of the FromCPU targets and any other
477 // non-FromCPU target. This way the remaining FromCPU targets
478 // issue a new request and get a fresh copy of the block and we
479 // avoid memory consistency violations.
480 if (pkt
->cmd
== MemCmd::ReadRespWithInvalidate
) {
481 auto it
= targets
.begin();
482 assert((it
->source
== Target::FromCPU
) ||
483 (it
->source
== Target::FromPrefetcher
));
484 ready_targets
.push_back(*it
);
485 it
= targets
.erase(it
);
486 while (it
!= targets
.end()) {
487 if (it
->source
== Target::FromCPU
) {
490 assert(it
->source
== Target::FromSnoop
);
491 ready_targets
.push_back(*it
);
492 it
= targets
.erase(it
);
495 ready_targets
.populateFlags();
497 std::swap(ready_targets
, targets
);
499 targets
.populateFlags();
501 return ready_targets
;
505 MSHR::promoteDeferredTargets()
507 if (targets
.empty() && deferredTargets
.empty()) {
508 // nothing to promote
512 // the deferred targets can be generally promoted unless they
513 // contain a cache maintenance request
515 // find the first target that is a cache maintenance request
516 auto it
= std::find_if(deferredTargets
.begin(), deferredTargets
.end(),
517 [](MSHR::Target
&t
) {
518 return t
.pkt
->req
->isCacheMaintenance();
520 if (it
== deferredTargets
.begin()) {
521 // if the first deferred target is a cache maintenance packet
522 // then we can promote provided the targets list is empty and
523 // we can service it on its own
524 if (targets
.empty()) {
525 targets
.splice(targets
.end(), deferredTargets
, it
);
528 // if a cache maintenance operation exists, we promote all the
529 // deferred targets that precede it, or all deferred targets
531 targets
.splice(targets
.end(), deferredTargets
,
532 deferredTargets
.begin(), it
);
535 deferredTargets
.populateFlags();
536 targets
.populateFlags();
537 order
= targets
.front().order
;
538 readyTime
= std::max(curTick(), targets
.front().readyTime
);
545 MSHR::promoteWritable()
547 if (deferredTargets
.needsWritable
&&
548 !(hasPostInvalidate() || hasPostDowngrade())) {
549 // We got a writable response, but we have deferred targets
550 // which are waiting to request a writable copy (not because
551 // of a pending invalidate). This can happen if the original
552 // request was for a read-only block, but we got a writable
553 // response anyway. Since we got the writable copy there's no
554 // need to defer the targets, so move them up to the regular
556 assert(!targets
.needsWritable
);
557 targets
.needsWritable
= true;
558 // if any of the deferred targets were upper-level cache
559 // requests marked downstreamPending, need to clear that
560 assert(!downstreamPending
); // not pending here anymore
561 deferredTargets
.clearDownstreamPending();
562 // this clears out deferredTargets too
563 targets
.splice(targets
.end(), deferredTargets
);
564 deferredTargets
.resetFlags();
570 MSHR::checkFunctional(PacketPtr pkt
)
572 // For printing, we treat the MSHR as a whole as single entity.
573 // For other requests, we iterate over the individual targets
574 // since that's where the actual data lies.
575 if (pkt
->isPrint()) {
576 pkt
->checkFunctional(this, blkAddr
, isSecure
, blkSize
, nullptr);
579 return (targets
.checkFunctional(pkt
) ||
580 deferredTargets
.checkFunctional(pkt
));
585 MSHR::sendPacket(BaseCache
&cache
)
587 return cache
.sendMSHRQueuePacket(this);
591 MSHR::print(std::ostream
&os
, int verbosity
, const std::string
&prefix
) const
593 ccprintf(os
, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s %s\n",
594 prefix
, blkAddr
, blkAddr
+ blkSize
- 1,
595 isSecure
? "s" : "ns",
596 isForward
? "Forward" : "",
597 allocOnFill() ? "AllocOnFill" : "",
598 needsWritable() ? "Wrtbl" : "",
599 _isUncacheable
? "Unc" : "",
600 inService
? "InSvc" : "",
601 downstreamPending
? "DwnPend" : "",
602 postInvalidate
? "PostInv" : "",
603 postDowngrade
? "PostDowngr" : "",
604 hasFromCache() ? "HasFromCache" : "");
606 if (!targets
.empty()) {
607 ccprintf(os
, "%s Targets:\n", prefix
);
608 targets
.print(os
, verbosity
, prefix
+ " ");
610 if (!deferredTargets
.empty()) {
611 ccprintf(os
, "%s Deferred Targets:\n", prefix
);
612 deferredTargets
.print(os
, verbosity
, prefix
+ " ");
619 std::ostringstream str
;