1/*
2 * Copyright (c) 2012-2013, 2015 ARM Limited
3 * All rights reserved.
4 *
5 * The license below extends only to copyright in the software and shall
6 * not be construed as granting a license to any other intellectual
7 * property including but not limited to intellectual property relating
8 * to a hardware implementation of the functionality of the software

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57#include "debug/Cache.hh"
58#include "mem/cache/cache.hh"
59#include "mem/cache/mshr.hh"
60#include "sim/core.hh"
61
62using namespace std;
63
64MSHR::MSHR() : readyTime(0), _isUncacheable(false), downstreamPending(false),
65 pendingDirty(false),
66 postInvalidate(false), postDowngrade(false),
67 queue(NULL), order(0), blkAddr(0),
68 blkSize(0), isSecure(false), inService(false),
69 isForward(false), allocOnFill(false),
70 data(NULL)
71{
72}
73
74
75MSHR::TargetList::TargetList()
76 : needsExclusive(false), hasUpgrade(false)
77{}
78
79
80inline void
81MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
82 Counter order, Target::Source source, bool markPending)
83{
84 if (source != Target::FromSnoop) {
85 if (pkt->needsExclusive()) {
86 needsExclusive = true;
87 }
88
89 // StoreCondReq is effectively an upgrade if it's in an MSHR
90 // since it would have been failed already if we didn't have a
91 // read-only copy
92 if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
93 hasUpgrade = true;
94 }

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233 assert(downstreamPending);
234 downstreamPending = false;
235 // recursively clear flag on any MSHRs we will be forwarding
236 // responses to
237 targets.clearDownstreamPending();
238}
239
240bool
241MSHR::markInService(bool pending_dirty_resp)
242{
243 assert(!inService);
244 if (isForwardNoResponse()) {
245 // we just forwarded the request packet & don't expect a
246 // response, so get rid of it
247 assert(getNumTargets() == 1);
248 popTarget();
249 return true;
250 }
251
252 inService = true;
253 pendingDirty = targets.needsExclusive || pending_dirty_resp;
254 postInvalidate = postDowngrade = false;
255
256 if (!downstreamPending) {
257 // let upstream caches know that the request has made it to a
258 // level where it's going to get a response
259 targets.clearDownstreamPending();
260 }
261 return false;

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292 allocOnFill = allocOnFill || alloc_on_fill;
293
294 // if there's a request already in service for this MSHR, we will
295 // have to defer the new target until after the response if any of
296 // the following are true:
297 // - there are other targets already deferred
298 // - there's a pending invalidate to be applied after the response
299 // comes back (but before this target is processed)
300 // - this target requires an exclusive block and either we're not
301 // getting an exclusive block back or we have already snooped
302 // another read request that will downgrade our exclusive block
303 // to shared
304 if (inService &&
305 (!deferredTargets.empty() || hasPostInvalidate() ||
306 (pkt->needsExclusive() &&
307 (!isPendingDirty() || hasPostDowngrade() || isForward)))) {
308 // need to put on deferred list
309 if (hasPostInvalidate())
310 replaceUpgrade(pkt);
311 deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true);
312 } else {
313 // No request outstanding, or still OK to append to
314 // outstanding request: append to regular target list. Only
315 // mark pending if current request hasn't been issued yet
316 // (isn't in service).
317 targets.add(pkt, whenReady, _order, Target::FromCPU, !inService);
318 }
319}
320
321bool
322MSHR::handleSnoop(PacketPtr pkt, Counter _order)
323{
324 DPRINTF(Cache, "%s for %s addr %#llx size %d\n", __func__,
325 pkt->cmdString(), pkt->getAddr(), pkt->getSize());
326
327 // when we snoop packets the needsExclusive and isInvalidate flags
328 // should always be the same, however, this assumes that we never
329 // snoop writes as they are currently not marked as invalidations
330 panic_if(pkt->needsExclusive() != pkt->isInvalidate(),
331 "%s got snoop %s to addr %#llx where needsExclusive, "
332 "does not match isInvalidate", name(), pkt->cmdString(),
333 pkt->getAddr());
334
335 if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
336 // Request has not been issued yet, or it's been issued
337 // locally but is buffered unissued at some downstream cache
338 // which is forwarding us this snoop. Either way, the packet
339 // we're snooping logically precedes this MSHR's request, so
340 // the snoop has no impact on the MSHR, but must be processed
341 // in the standard way by the cache. The only exception is
342 // that if we're an L2+ cache buffering an UpgradeReq from a
343 // higher-level cache, and the snoop is invalidating, then our
344 // buffered upgrades must be converted to read exclusives,
345 // since the upper-level cache no longer has a valid copy.
346 // That is, even though the upper-level cache got out on its
347 // local bus first, some other invalidating transaction
348 // reached the global bus before the upgrade did.
349 if (pkt->needsExclusive()) {
350 targets.replaceUpgrades();
351 deferredTargets.replaceUpgrades();
352 }
353
354 return false;
355 }
356
357 // From here on down, the request issued by this MSHR logically
358 // precedes the request we're snooping.
359 if (pkt->needsExclusive()) {
360 // snooped request still precedes the re-request we'll have to
361 // issue for deferred targets, if any...
362 deferredTargets.replaceUpgrades();
363 }
364
365 if (hasPostInvalidate()) {
366 // a prior snoop has already appended an invalidation, so
367 // logically we don't have the block anymore; no need for
368 // further snooping.
369 return true;
370 }
371
372 if (isPendingDirty() || pkt->isInvalidate()) {
373 // We need to save and replay the packet in two cases:
374 // 1. We're awaiting an exclusive copy, so ownership is pending,
375 // and we need to deal with the snoop after we receive data.
376 // 2. It's an invalidation (e.g., UpgradeReq), and we need
377 // to forward the snoop up the hierarchy after the current
378 // transaction completes.
379
380 // Start by determining if we will eventually respond or not,
381 // matching the conditions checked in Cache::handleSnoop
382 bool will_respond = isPendingDirty() && pkt->needsResponse() &&
383 pkt->cmd != MemCmd::InvalidateReq;
384
385 // The packet we are snooping may be deleted by the time we
386 // actually process the target, and we consequently need to
387 // save a copy here. Clear flags and also allocate new data as
388 // the original packet data storage may have been deleted by
389 // the time we get to process this packet. In the cases where
390 // we are not responding after handling the snoop we also need
391 // to create a copy of the request to be on the safe side. In
392 // the latter case the cache is responsible for deleting both
393 // the packet and the request as part of handling the deferred
394 // snoop.
395 PacketPtr cp_pkt = will_respond ? new Packet(pkt, true, true) :
396 new Packet(new Request(*pkt->req), pkt->cmd);
397
398 if (isPendingDirty()) {
399 // The new packet will need to get the response from the
400 // MSHR already queued up here
401 pkt->assertMemInhibit();
402 // in the case of an uncacheable request there is no need
403 // to set the exclusive flag, but since the recipient does
404 // not care there is no harm in doing so
405 pkt->setSupplyExclusive();
406 }
407 targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
408 downstreamPending && targets.needsExclusive);
409
410 if (pkt->needsExclusive()) {
411 // This transaction will take away our pending copy
412 postInvalidate = true;
413 }
414 }
415
416 if (!pkt->needsExclusive() && !pkt->req->isUncacheable()) {
417 // This transaction will get a read-shared copy, downgrading
418 // our copy if we had an exclusive one
419 postDowngrade = true;
420 pkt->assertShared();
421 }
422
423 return true;
424}
425
426
427bool
428MSHR::promoteDeferredTargets()

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441 order = targets.front().order;
442 readyTime = std::max(curTick(), targets.front().readyTime);
443
444 return true;
445}
446
447
448void
449MSHR::promoteExclusive()
450{
451 if (deferredTargets.needsExclusive &&
452 !(hasPostInvalidate() || hasPostDowngrade())) {
453 // We got an exclusive response, but we have deferred targets
454 // which are waiting to request an exclusive copy (not because
455 // of a pending invalidate). This can happen if the original
456 // request was for a read-only (non-exclusive) block, but we
457 // got an exclusive copy anyway because of the E part of the
458 // MOESI/MESI protocol. Since we got the exclusive copy
459 // there's no need to defer the targets, so move them up to
460 // the regular target list.
461 assert(!targets.needsExclusive);
462 targets.needsExclusive = true;
463 // if any of the deferred targets were upper-level cache
464 // requests marked downstreamPending, need to clear that
465 assert(!downstreamPending); // not pending here anymore
466 deferredTargets.clearDownstreamPending();
467 // this clears out deferredTargets too
468 targets.splice(targets.end(), deferredTargets);
469 deferredTargets.resetFlags();
470 }

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491MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
492{
493 ccprintf(os, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
494 prefix, blkAddr, blkAddr + blkSize - 1,
495 isSecure ? "s" : "ns",
496 isForward ? "Forward" : "",
497 allocOnFill ? "AllocOnFill" : "",
498 isForwardNoResponse() ? "ForwNoResp" : "",
499 needsExclusive() ? "Excl" : "",
500 _isUncacheable ? "Unc" : "",
501 inService ? "InSvc" : "",
502 downstreamPending ? "DwnPend" : "",
503 hasPostInvalidate() ? "PostInv" : "",
504 hasPostDowngrade() ? "PostDowngr" : "");
505
506 ccprintf(os, "%s Targets:\n", prefix);
507 targets.print(os, verbosity, prefix + " ");

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