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15 * Copyright (c) 2010 Advanced Micro Devices, Inc.
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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"
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 // - this target requires a writable block and either we're not
322 // getting a writable block back or we have already snooped
323 // another read request that will downgrade our writable block
324 // to non-writable (Shared or Owned)
326 (!deferredTargets
.empty() || hasPostInvalidate() ||
327 (pkt
->needsWritable() &&
328 (!isPendingModified() || hasPostDowngrade() || isForward
)))) {
329 // need to put on deferred list
330 if (hasPostInvalidate())
332 deferredTargets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, true,
335 // No request outstanding, or still OK to append to
336 // outstanding request: append to regular target list. Only
337 // mark pending if current request hasn't been issued yet
338 // (isn't in service).
339 targets
.add(pkt
, whenReady
, _order
, Target::FromCPU
, !inService
,
345 MSHR::handleSnoop(PacketPtr pkt
, Counter _order
)
347 DPRINTF(Cache
, "%s for %s\n", __func__
, pkt
->print());
349 // when we snoop packets the needsWritable and isInvalidate flags
350 // should always be the same, however, this assumes that we never
351 // snoop writes as they are currently not marked as invalidations
352 panic_if(pkt
->needsWritable() != pkt
->isInvalidate(),
353 "%s got snoop %s where needsWritable, "
354 "does not match isInvalidate", name(), pkt
->print());
356 if (!inService
|| (pkt
->isExpressSnoop() && downstreamPending
)) {
357 // Request has not been issued yet, or it's been issued
358 // locally but is buffered unissued at some downstream cache
359 // which is forwarding us this snoop. Either way, the packet
360 // we're snooping logically precedes this MSHR's request, so
361 // the snoop has no impact on the MSHR, but must be processed
362 // in the standard way by the cache. The only exception is
363 // that if we're an L2+ cache buffering an UpgradeReq from a
364 // higher-level cache, and the snoop is invalidating, then our
365 // buffered upgrades must be converted to read exclusives,
366 // since the upper-level cache no longer has a valid copy.
367 // That is, even though the upper-level cache got out on its
368 // local bus first, some other invalidating transaction
369 // reached the global bus before the upgrade did.
370 if (pkt
->needsWritable()) {
371 targets
.replaceUpgrades();
372 deferredTargets
.replaceUpgrades();
378 // From here on down, the request issued by this MSHR logically
379 // precedes the request we're snooping.
380 if (pkt
->needsWritable()) {
381 // snooped request still precedes the re-request we'll have to
382 // issue for deferred targets, if any...
383 deferredTargets
.replaceUpgrades();
386 if (hasPostInvalidate()) {
387 // a prior snoop has already appended an invalidation, so
388 // logically we don't have the block anymore; no need for
393 if (isPendingModified() || pkt
->isInvalidate()) {
394 // We need to save and replay the packet in two cases:
395 // 1. We're awaiting a writable copy (Modified or Exclusive),
396 // so this MSHR is the orgering point, and we need to respond
397 // after we receive data.
398 // 2. It's an invalidation (e.g., UpgradeReq), and we need
399 // to forward the snoop up the hierarchy after the current
400 // transaction completes.
402 // Start by determining if we will eventually respond or not,
403 // matching the conditions checked in Cache::handleSnoop
404 bool will_respond
= isPendingModified() && pkt
->needsResponse();
406 // The packet we are snooping may be deleted by the time we
407 // actually process the target, and we consequently need to
408 // save a copy here. Clear flags and also allocate new data as
409 // the original packet data storage may have been deleted by
410 // the time we get to process this packet. In the cases where
411 // we are not responding after handling the snoop we also need
412 // to create a copy of the request to be on the safe side. In
413 // the latter case the cache is responsible for deleting both
414 // the packet and the request as part of handling the deferred
416 PacketPtr cp_pkt
= will_respond
? new Packet(pkt
, true, true) :
417 new Packet(new Request(*pkt
->req
), pkt
->cmd
, blkSize
);
420 // we are the ordering point, and will consequently
421 // respond, and depending on whether the packet
422 // needsWritable or not we either pass a Shared line or a
424 pkt
->setCacheResponding();
426 // inform the cache hierarchy that this cache had the line
427 // in the Modified state, even if the response is passed
428 // as Shared (and thus non-writable)
429 pkt
->setResponderHadWritable();
431 // in the case of an uncacheable request there is no need
432 // to set the responderHadWritable flag, but since the
433 // recipient does not care there is no harm in doing so
435 targets
.add(cp_pkt
, curTick(), _order
, Target::FromSnoop
,
436 downstreamPending
&& targets
.needsWritable
, false);
438 if (pkt
->needsWritable()) {
439 // This transaction will take away our pending copy
440 postInvalidate
= true;
444 if (!pkt
->needsWritable() && !pkt
->req
->isUncacheable()) {
445 // This transaction will get a read-shared copy, downgrading
446 // our copy if we had a writable one
447 postDowngrade
= true;
448 // make sure that any downstream cache does not respond with a
449 // writable (and dirty) copy even if it has one, unless it was
450 // explicitly asked for one
451 pkt
->setHasSharers();
458 MSHR::extractServiceableTargets(PacketPtr pkt
)
460 TargetList ready_targets
;
461 // If the downstream MSHR got an invalidation request then we only
462 // service the first of the FromCPU targets and any other
463 // non-FromCPU target. This way the remaining FromCPU targets
464 // issue a new request and get a fresh copy of the block and we
465 // avoid memory consistency violations.
466 if (pkt
->cmd
== MemCmd::ReadRespWithInvalidate
) {
467 auto it
= targets
.begin();
468 assert((it
->source
== Target::FromCPU
) ||
469 (it
->source
== Target::FromPrefetcher
));
470 ready_targets
.push_back(*it
);
471 it
= targets
.erase(it
);
472 while (it
!= targets
.end()) {
473 if (it
->source
== Target::FromCPU
) {
476 assert(it
->source
== Target::FromSnoop
);
477 ready_targets
.push_back(*it
);
478 it
= targets
.erase(it
);
481 ready_targets
.populateFlags();
483 std::swap(ready_targets
, targets
);
485 targets
.populateFlags();
487 return ready_targets
;
491 MSHR::promoteDeferredTargets()
493 if (targets
.empty()) {
494 if (deferredTargets
.empty()) {
498 std::swap(targets
, deferredTargets
);
500 // If the targets list is not empty then we have one targets
501 // from the deferredTargets list to the targets list. A new
502 // request will then service the targets list.
503 targets
.splice(targets
.end(), deferredTargets
);
504 targets
.populateFlags();
507 // clear deferredTargets flags
508 deferredTargets
.resetFlags();
510 order
= targets
.front().order
;
511 readyTime
= std::max(curTick(), targets
.front().readyTime
);
518 MSHR::promoteWritable()
520 if (deferredTargets
.needsWritable
&&
521 !(hasPostInvalidate() || hasPostDowngrade())) {
522 // We got a writable response, but we have deferred targets
523 // which are waiting to request a writable copy (not because
524 // of a pending invalidate). This can happen if the original
525 // request was for a read-only block, but we got a writable
526 // response anyway. Since we got the writable copy there's no
527 // need to defer the targets, so move them up to the regular
529 assert(!targets
.needsWritable
);
530 targets
.needsWritable
= true;
531 // if any of the deferred targets were upper-level cache
532 // requests marked downstreamPending, need to clear that
533 assert(!downstreamPending
); // not pending here anymore
534 deferredTargets
.clearDownstreamPending();
535 // this clears out deferredTargets too
536 targets
.splice(targets
.end(), deferredTargets
);
537 deferredTargets
.resetFlags();
543 MSHR::checkFunctional(PacketPtr pkt
)
545 // For printing, we treat the MSHR as a whole as single entity.
546 // For other requests, we iterate over the individual targets
547 // since that's where the actual data lies.
548 if (pkt
->isPrint()) {
549 pkt
->checkFunctional(this, blkAddr
, isSecure
, blkSize
, nullptr);
552 return (targets
.checkFunctional(pkt
) ||
553 deferredTargets
.checkFunctional(pkt
));
558 MSHR::sendPacket(Cache
&cache
)
560 return cache
.sendMSHRQueuePacket(this);
564 MSHR::print(std::ostream
&os
, int verbosity
, const std::string
&prefix
) const
566 ccprintf(os
, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
567 prefix
, blkAddr
, blkAddr
+ blkSize
- 1,
568 isSecure
? "s" : "ns",
569 isForward
? "Forward" : "",
570 allocOnFill() ? "AllocOnFill" : "",
571 needsWritable() ? "Wrtbl" : "",
572 _isUncacheable
? "Unc" : "",
573 inService
? "InSvc" : "",
574 downstreamPending
? "DwnPend" : "",
575 postInvalidate
? "PostInv" : "",
576 postDowngrade
? "PostDowngr" : "");
578 if (!targets
.empty()) {
579 ccprintf(os
, "%s Targets:\n", prefix
);
580 targets
.print(os
, verbosity
, prefix
+ " ");
582 if (!deferredTargets
.empty()) {
583 ccprintf(os
, "%s Deferred Targets:\n", prefix
);
584 deferredTargets
.print(os
, verbosity
, prefix
+ " ");