61#include "sim/core.hh"
62
63MSHR::MSHR() : downstreamPending(false),
64 pendingModified(false),
65 postInvalidate(false), postDowngrade(false),
66 isForward(false)
67{
68}
69
70MSHR::TargetList::TargetList()
71 : needsWritable(false), hasUpgrade(false), allocOnFill(false),
72 hasFromCache(false)
73{}
74
75
76void
77MSHR::TargetList::updateFlags(PacketPtr pkt, Target::Source source,
78 bool alloc_on_fill)
79{
80 if (source != Target::FromSnoop) {
81 if (pkt->needsWritable()) {
82 needsWritable = true;
83 }
84
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
87 // read-only copy
88 if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
89 hasUpgrade = true;
90 }
91
92 // potentially re-evaluate whether we should allocate on a fill or
93 // not
94 allocOnFill = allocOnFill || alloc_on_fill;
95
96 if (source != Target::FromPrefetcher) {
97 hasFromCache = hasFromCache || pkt->fromCache();
98 }
99 }
100}
101
102void
103MSHR::TargetList::populateFlags()
104{
105 resetFlags();
106 for (auto& t: *this) {
107 updateFlags(t.pkt, t.source, t.allocOnFill);
108 }
109}
110
111inline void
112MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
113 Counter order, Target::Source source, bool markPending,
114 bool alloc_on_fill)
115{
116 updateFlags(pkt, source, alloc_on_fill);
117 if (markPending) {
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;
125 } else {
126 // No need to clear downstreamPending later
127 markPending = false;
128 }
129 }
130
131 emplace_back(pkt, readyTime, order, source, markPending, alloc_on_fill);
132}
133
134
135static void
136replaceUpgrade(PacketPtr pkt)
137{
138 // remember if the current packet has data allocated
139 bool has_data = pkt->hasData() || pkt->hasRespData();
140
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");
150 }
151
152 if (!has_data) {
153 // there is no sensible way of setting the data field if the
154 // new command actually would carry data
155 assert(!pkt->hasData());
156
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
161 pkt->allocate();
162 }
163 }
164}
165
166
167void
168MSHR::TargetList::replaceUpgrades()
169{
170 if (!hasUpgrade)
171 return;
172
173 for (auto& t : *this) {
174 replaceUpgrade(t.pkt);
175 }
176
177 hasUpgrade = false;
178}
179
180
181void
182MSHR::TargetList::clearDownstreamPending()
183{
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
191 // passed through.
192 MSHR *mshr = t.pkt->findNextSenderState<MSHR>();
193 if (mshr != nullptr) {
194 mshr->clearDownstreamPending();
195 }
196 t.markedPending = false;
197 }
198 }
199}
200
201
202bool
203MSHR::TargetList::checkFunctional(PacketPtr pkt)
204{
205 for (auto& t : *this) {
206 if (pkt->checkFunctional(t.pkt)) {
207 return true;
208 }
209 }
210
211 return false;
212}
213
214
215void
216MSHR::TargetList::print(std::ostream &os, int verbosity,
217 const std::string &prefix) const
218{
219 for (auto& t : *this) {
220 const char *s;
221 switch (t.source) {
222 case Target::FromCPU:
223 s = "FromCPU";
224 break;
225 case Target::FromSnoop:
226 s = "FromSnoop";
227 break;
228 case Target::FromPrefetcher:
229 s = "FromPrefetcher";
230 break;
231 default:
232 s = "";
233 break;
234 }
235 ccprintf(os, "%s%s: ", prefix, s);
236 t.pkt->print(os, verbosity, "");
237 ccprintf(os, "\n");
238 }
239}
240
241
242void
243MSHR::allocate(Addr blk_addr, unsigned blk_size, PacketPtr target,
244 Tick when_ready, Counter _order, bool alloc_on_fill)
245{
246 blkAddr = blk_addr;
247 blkSize = blk_size;
248 isSecure = target->isSecure();
249 readyTime = when_ready;
250 order = _order;
251 assert(target);
252 isForward = false;
253 _isUncacheable = target->req->isUncacheable();
254 inService = false;
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());
263}
264
265
266void
267MSHR::clearDownstreamPending()
268{
269 assert(downstreamPending);
270 downstreamPending = false;
271 // recursively clear flag on any MSHRs we will be forwarding
272 // responses to
273 targets.clearDownstreamPending();
274}
275
276void
277MSHR::markInService(bool pending_modified_resp)
278{
279 assert(!inService);
280
281 inService = true;
282 pendingModified = targets.needsWritable || pending_modified_resp;
283 postInvalidate = postDowngrade = false;
284
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();
289 }
290}
291
292
293void
294MSHR::deallocate()
295{
296 assert(targets.empty());
297 targets.resetFlags();
298 assert(deferredTargets.isReset());
299 inService = false;
300}
301
302/*
303 * Adds a target to an MSHR
304 */
305void
306MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order,
307 bool alloc_on_fill)
308{
309 // assume we'd never issue a prefetch when we've got an
310 // outstanding miss
311 assert(pkt->cmd != MemCmd::HardPFReq);
312
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() ||
331 (inService &&
332 (hasPostInvalidate() ||
333 (pkt->needsWritable() &&
334 (!isPendingModified() || hasPostDowngrade() || isForward))))) {
335 // need to put on deferred list
336 if (inService && hasPostInvalidate())
337 replaceUpgrade(pkt);
338 deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true,
339 alloc_on_fill);
340 } else {
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,
346 alloc_on_fill);
347 }
348}
349
350bool
351MSHR::handleSnoop(PacketPtr pkt, Counter _order)
352{
353 DPRINTF(Cache, "%s for %s\n", __func__, pkt->print());
354
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());
362
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();
380 }
381
382 return false;
383 }
384
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();
391 }
392
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
398 // snooping.
399 return true;
400 }
401
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.
410
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() &&
414 !pkt->isClean();
415
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
425 // snoop.
426 PacketPtr cp_pkt = will_respond ? new Packet(pkt, true, true) :
427 new Packet(new Request(*pkt->req), pkt->cmd, blkSize, pkt->id);
428
429 if (will_respond) {
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
433 // Modified line
434 pkt->setCacheResponding();
435
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();
440
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
444 }
445 targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
446 downstreamPending && targets.needsWritable, false);
447
448 if (pkt->needsWritable() || pkt->isInvalidate()) {
449 // This transaction will take away our pending copy
450 postInvalidate = true;
451 }
452
453 if (isPendingModified() && pkt->isClean()) {
454 pkt->setSatisfied();
455 }
456 }
457
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();
466 }
467
468 return true;
469}
470
471MSHR::TargetList
472MSHR::extractServiceableTargets(PacketPtr pkt)
473{
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) {
488 it++;
489 } else {
490 assert(it->source == Target::FromSnoop);
491 ready_targets.push_back(*it);
492 it = targets.erase(it);
493 }
494 }
495 ready_targets.populateFlags();
496 } else {
497 std::swap(ready_targets, targets);
498 }
499 targets.populateFlags();
500
501 return ready_targets;
502}
503
504bool
505MSHR::promoteDeferredTargets()
506{
507 if (targets.empty() && deferredTargets.empty()) {
508 // nothing to promote
509 return false;
510 }
511
512 // the deferred targets can be generally promoted unless they
513 // contain a cache maintenance request
514
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();
519 });
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);
526 }
527 } else {
528 // if a cache maintenance operation exists, we promote all the
529 // deferred targets that precede it, or all deferred targets
530 // otherwise
531 targets.splice(targets.end(), deferredTargets,
532 deferredTargets.begin(), it);
533 }
534
535 deferredTargets.populateFlags();
536 targets.populateFlags();
537 order = targets.front().order;
538 readyTime = std::max(curTick(), targets.front().readyTime);
539
540 return true;
541}
542
543
544void
545MSHR::promoteWritable()
546{
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
555 // target list.
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();
565 }
566}
567
568
569bool
570MSHR::checkFunctional(PacketPtr pkt)
571{
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);
577 return false;
578 } else {
579 return (targets.checkFunctional(pkt) ||
580 deferredTargets.checkFunctional(pkt));
581 }
582}
583
584bool
585MSHR::sendPacket(BaseCache &cache)
586{
587 return cache.sendMSHRQueuePacket(this);
588}
589
590void
591MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
592{
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" : "");
605
606 if (!targets.empty()) {
607 ccprintf(os, "%s Targets:\n", prefix);
608 targets.print(os, verbosity, prefix + " ");
609 }
610 if (!deferredTargets.empty()) {
611 ccprintf(os, "%s Deferred Targets:\n", prefix);
612 deferredTargets.print(os, verbosity, prefix + " ");
613 }
614}
615
616std::string
617MSHR::print() const
618{
619 std::ostringstream str;
620 print(str);
621 return str.str();
622}
|