cache.cc revision 13017
1/* 2 * Copyright (c) 2010-2018 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 9 * licensed hereunder. You may use the software subject to the license 10 * terms below provided that you ensure that this notice is replicated 11 * unmodified and in its entirety in all distributions of the software, 12 * modified or unmodified, in source code or in binary form. 13 * 14 * Copyright (c) 2002-2005 The Regents of The University of Michigan 15 * Copyright (c) 2010,2015 Advanced Micro Devices, Inc. 16 * All rights reserved. 17 * 18 * Redistribution and use in source and binary forms, with or without 19 * modification, are permitted provided that the following conditions are 20 * met: redistributions of source code must retain the above copyright 21 * notice, this list of conditions and the following disclaimer; 22 * redistributions in binary form must reproduce the above copyright 23 * notice, this list of conditions and the following disclaimer in the 24 * documentation and/or other materials provided with the distribution; 25 * neither the name of the copyright holders nor the names of its 26 * contributors may be used to endorse or promote products derived from 27 * this software without specific prior written permission. 28 * 29 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 30 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 31 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 32 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 33 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 34 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 35 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 36 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 37 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 38 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 39 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 40 * 41 * Authors: Erik Hallnor 42 * Dave Greene 43 * Nathan Binkert 44 * Steve Reinhardt 45 * Ron Dreslinski 46 * Andreas Sandberg 47 * Nikos Nikoleris 48 */ 49 50/** 51 * @file 52 * Cache definitions. 53 */ 54 55#include "mem/cache/cache.hh" 56 57#include <cassert> 58 59#include "base/compiler.hh" 60#include "base/logging.hh" 61#include "base/trace.hh" 62#include "base/types.hh" 63#include "debug/Cache.hh" 64#include "debug/CacheTags.hh" 65#include "debug/CacheVerbose.hh" 66#include "enums/Clusivity.hh" 67#include "mem/cache/blk.hh" 68#include "mem/cache/mshr.hh" 69#include "mem/cache/tags/base.hh" 70#include "mem/cache/write_queue_entry.hh" 71#include "mem/request.hh" 72#include "params/Cache.hh" 73 74Cache::Cache(const CacheParams *p) 75 : BaseCache(p, p->system->cacheLineSize()), 76 doFastWrites(true) 77{ 78} 79 80void 81Cache::satisfyRequest(PacketPtr pkt, CacheBlk *blk, 82 bool deferred_response, bool pending_downgrade) 83{ 84 BaseCache::satisfyRequest(pkt, blk); 85 86 if (pkt->isRead()) { 87 // determine if this read is from a (coherent) cache or not 88 if (pkt->fromCache()) { 89 assert(pkt->getSize() == blkSize); 90 // special handling for coherent block requests from 91 // upper-level caches 92 if (pkt->needsWritable()) { 93 // sanity check 94 assert(pkt->cmd == MemCmd::ReadExReq || 95 pkt->cmd == MemCmd::SCUpgradeFailReq); 96 assert(!pkt->hasSharers()); 97 98 // if we have a dirty copy, make sure the recipient 99 // keeps it marked dirty (in the modified state) 100 if (blk->isDirty()) { 101 pkt->setCacheResponding(); 102 blk->status &= ~BlkDirty; 103 } 104 } else if (blk->isWritable() && !pending_downgrade && 105 !pkt->hasSharers() && 106 pkt->cmd != MemCmd::ReadCleanReq) { 107 // we can give the requester a writable copy on a read 108 // request if: 109 // - we have a writable copy at this level (& below) 110 // - we don't have a pending snoop from below 111 // signaling another read request 112 // - no other cache above has a copy (otherwise it 113 // would have set hasSharers flag when 114 // snooping the packet) 115 // - the read has explicitly asked for a clean 116 // copy of the line 117 if (blk->isDirty()) { 118 // special considerations if we're owner: 119 if (!deferred_response) { 120 // respond with the line in Modified state 121 // (cacheResponding set, hasSharers not set) 122 pkt->setCacheResponding(); 123 124 // if this cache is mostly inclusive, we 125 // keep the block in the Exclusive state, 126 // and pass it upwards as Modified 127 // (writable and dirty), hence we have 128 // multiple caches, all on the same path 129 // towards memory, all considering the 130 // same block writable, but only one 131 // considering it Modified 132 133 // we get away with multiple caches (on 134 // the same path to memory) considering 135 // the block writeable as we always enter 136 // the cache hierarchy through a cache, 137 // and first snoop upwards in all other 138 // branches 139 blk->status &= ~BlkDirty; 140 } else { 141 // if we're responding after our own miss, 142 // there's a window where the recipient didn't 143 // know it was getting ownership and may not 144 // have responded to snoops correctly, so we 145 // have to respond with a shared line 146 pkt->setHasSharers(); 147 } 148 } 149 } else { 150 // otherwise only respond with a shared copy 151 pkt->setHasSharers(); 152 } 153 } 154 } 155} 156 157///////////////////////////////////////////////////// 158// 159// Access path: requests coming in from the CPU side 160// 161///////////////////////////////////////////////////// 162 163bool 164Cache::access(PacketPtr pkt, CacheBlk *&blk, Cycles &lat, 165 PacketList &writebacks) 166{ 167 168 if (pkt->req->isUncacheable()) { 169 assert(pkt->isRequest()); 170 171 chatty_assert(!(isReadOnly && pkt->isWrite()), 172 "Should never see a write in a read-only cache %s\n", 173 name()); 174 175 DPRINTF(Cache, "%s for %s\n", __func__, pkt->print()); 176 177 // flush and invalidate any existing block 178 CacheBlk *old_blk(tags->findBlock(pkt->getAddr(), pkt->isSecure())); 179 if (old_blk && old_blk->isValid()) { 180 evictBlock(old_blk, writebacks); 181 } 182 183 blk = nullptr; 184 // lookupLatency is the latency in case the request is uncacheable. 185 lat = lookupLatency; 186 return false; 187 } 188 189 return BaseCache::access(pkt, blk, lat, writebacks); 190} 191 192void 193Cache::doWritebacks(PacketList& writebacks, Tick forward_time) 194{ 195 while (!writebacks.empty()) { 196 PacketPtr wbPkt = writebacks.front(); 197 // We use forwardLatency here because we are copying writebacks to 198 // write buffer. 199 200 // Call isCachedAbove for Writebacks, CleanEvicts and 201 // WriteCleans to discover if the block is cached above. 202 if (isCachedAbove(wbPkt)) { 203 if (wbPkt->cmd == MemCmd::CleanEvict) { 204 // Delete CleanEvict because cached copies exist above. The 205 // packet destructor will delete the request object because 206 // this is a non-snoop request packet which does not require a 207 // response. 208 delete wbPkt; 209 } else if (wbPkt->cmd == MemCmd::WritebackClean) { 210 // clean writeback, do not send since the block is 211 // still cached above 212 assert(writebackClean); 213 delete wbPkt; 214 } else { 215 assert(wbPkt->cmd == MemCmd::WritebackDirty || 216 wbPkt->cmd == MemCmd::WriteClean); 217 // Set BLOCK_CACHED flag in Writeback and send below, so that 218 // the Writeback does not reset the bit corresponding to this 219 // address in the snoop filter below. 220 wbPkt->setBlockCached(); 221 allocateWriteBuffer(wbPkt, forward_time); 222 } 223 } else { 224 // If the block is not cached above, send packet below. Both 225 // CleanEvict and Writeback with BLOCK_CACHED flag cleared will 226 // reset the bit corresponding to this address in the snoop filter 227 // below. 228 allocateWriteBuffer(wbPkt, forward_time); 229 } 230 writebacks.pop_front(); 231 } 232} 233 234void 235Cache::doWritebacksAtomic(PacketList& writebacks) 236{ 237 while (!writebacks.empty()) { 238 PacketPtr wbPkt = writebacks.front(); 239 // Call isCachedAbove for both Writebacks and CleanEvicts. If 240 // isCachedAbove returns true we set BLOCK_CACHED flag in Writebacks 241 // and discard CleanEvicts. 242 if (isCachedAbove(wbPkt, false)) { 243 if (wbPkt->cmd == MemCmd::WritebackDirty || 244 wbPkt->cmd == MemCmd::WriteClean) { 245 // Set BLOCK_CACHED flag in Writeback and send below, 246 // so that the Writeback does not reset the bit 247 // corresponding to this address in the snoop filter 248 // below. We can discard CleanEvicts because cached 249 // copies exist above. Atomic mode isCachedAbove 250 // modifies packet to set BLOCK_CACHED flag 251 memSidePort.sendAtomic(wbPkt); 252 } 253 } else { 254 // If the block is not cached above, send packet below. Both 255 // CleanEvict and Writeback with BLOCK_CACHED flag cleared will 256 // reset the bit corresponding to this address in the snoop filter 257 // below. 258 memSidePort.sendAtomic(wbPkt); 259 } 260 writebacks.pop_front(); 261 // In case of CleanEvicts, the packet destructor will delete the 262 // request object because this is a non-snoop request packet which 263 // does not require a response. 264 delete wbPkt; 265 } 266} 267 268 269void 270Cache::recvTimingSnoopResp(PacketPtr pkt) 271{ 272 DPRINTF(Cache, "%s for %s\n", __func__, pkt->print()); 273 274 // determine if the response is from a snoop request we created 275 // (in which case it should be in the outstandingSnoop), or if we 276 // merely forwarded someone else's snoop request 277 const bool forwardAsSnoop = outstandingSnoop.find(pkt->req) == 278 outstandingSnoop.end(); 279 280 if (!forwardAsSnoop) { 281 // the packet came from this cache, so sink it here and do not 282 // forward it 283 assert(pkt->cmd == MemCmd::HardPFResp); 284 285 outstandingSnoop.erase(pkt->req); 286 287 DPRINTF(Cache, "Got prefetch response from above for addr " 288 "%#llx (%s)\n", pkt->getAddr(), pkt->isSecure() ? "s" : "ns"); 289 recvTimingResp(pkt); 290 return; 291 } 292 293 // forwardLatency is set here because there is a response from an 294 // upper level cache. 295 // To pay the delay that occurs if the packet comes from the bus, 296 // we charge also headerDelay. 297 Tick snoop_resp_time = clockEdge(forwardLatency) + pkt->headerDelay; 298 // Reset the timing of the packet. 299 pkt->headerDelay = pkt->payloadDelay = 0; 300 memSidePort.schedTimingSnoopResp(pkt, snoop_resp_time); 301} 302 303void 304Cache::promoteWholeLineWrites(PacketPtr pkt) 305{ 306 // Cache line clearing instructions 307 if (doFastWrites && (pkt->cmd == MemCmd::WriteReq) && 308 (pkt->getSize() == blkSize) && (pkt->getOffset(blkSize) == 0)) { 309 pkt->cmd = MemCmd::WriteLineReq; 310 DPRINTF(Cache, "packet promoted from Write to WriteLineReq\n"); 311 } 312} 313 314void 315Cache::handleTimingReqHit(PacketPtr pkt, CacheBlk *blk, Tick request_time) 316{ 317 // should never be satisfying an uncacheable access as we 318 // flush and invalidate any existing block as part of the 319 // lookup 320 assert(!pkt->req->isUncacheable()); 321 322 BaseCache::handleTimingReqHit(pkt, blk, request_time); 323} 324 325void 326Cache::handleTimingReqMiss(PacketPtr pkt, CacheBlk *blk, Tick forward_time, 327 Tick request_time) 328{ 329 if (pkt->req->isUncacheable()) { 330 // ignore any existing MSHR if we are dealing with an 331 // uncacheable request 332 333 // should have flushed and have no valid block 334 assert(!blk || !blk->isValid()); 335 336 mshr_uncacheable[pkt->cmdToIndex()][pkt->req->masterId()]++; 337 338 if (pkt->isWrite()) { 339 allocateWriteBuffer(pkt, forward_time); 340 } else { 341 assert(pkt->isRead()); 342 343 // uncacheable accesses always allocate a new MSHR 344 345 // Here we are using forward_time, modelling the latency of 346 // a miss (outbound) just as forwardLatency, neglecting the 347 // lookupLatency component. 348 allocateMissBuffer(pkt, forward_time); 349 } 350 351 return; 352 } 353 354 Addr blk_addr = pkt->getBlockAddr(blkSize); 355 356 MSHR *mshr = mshrQueue.findMatch(blk_addr, pkt->isSecure()); 357 358 // Software prefetch handling: 359 // To keep the core from waiting on data it won't look at 360 // anyway, send back a response with dummy data. Miss handling 361 // will continue asynchronously. Unfortunately, the core will 362 // insist upon freeing original Packet/Request, so we have to 363 // create a new pair with a different lifecycle. Note that this 364 // processing happens before any MSHR munging on the behalf of 365 // this request because this new Request will be the one stored 366 // into the MSHRs, not the original. 367 if (pkt->cmd.isSWPrefetch()) { 368 assert(pkt->needsResponse()); 369 assert(pkt->req->hasPaddr()); 370 assert(!pkt->req->isUncacheable()); 371 372 // There's no reason to add a prefetch as an additional target 373 // to an existing MSHR. If an outstanding request is already 374 // in progress, there is nothing for the prefetch to do. 375 // If this is the case, we don't even create a request at all. 376 PacketPtr pf = nullptr; 377 378 if (!mshr) { 379 // copy the request and create a new SoftPFReq packet 380 RequestPtr req = std::make_shared<Request>(pkt->req->getPaddr(), 381 pkt->req->getSize(), 382 pkt->req->getFlags(), 383 pkt->req->masterId()); 384 pf = new Packet(req, pkt->cmd); 385 pf->allocate(); 386 assert(pf->getAddr() == pkt->getAddr()); 387 assert(pf->getSize() == pkt->getSize()); 388 } 389 390 pkt->makeTimingResponse(); 391 392 // request_time is used here, taking into account lat and the delay 393 // charged if the packet comes from the xbar. 394 cpuSidePort.schedTimingResp(pkt, request_time, true); 395 396 // If an outstanding request is in progress (we found an 397 // MSHR) this is set to null 398 pkt = pf; 399 } 400 401 BaseCache::handleTimingReqMiss(pkt, mshr, blk, forward_time, request_time); 402} 403 404void 405Cache::recvTimingReq(PacketPtr pkt) 406{ 407 DPRINTF(CacheTags, "%s tags:\n%s\n", __func__, tags->print()); 408 409 promoteWholeLineWrites(pkt); 410 411 if (pkt->cacheResponding()) { 412 // a cache above us (but not where the packet came from) is 413 // responding to the request, in other words it has the line 414 // in Modified or Owned state 415 DPRINTF(Cache, "Cache above responding to %s: not responding\n", 416 pkt->print()); 417 418 // if the packet needs the block to be writable, and the cache 419 // that has promised to respond (setting the cache responding 420 // flag) is not providing writable (it is in Owned rather than 421 // the Modified state), we know that there may be other Shared 422 // copies in the system; go out and invalidate them all 423 assert(pkt->needsWritable() && !pkt->responderHadWritable()); 424 425 // an upstream cache that had the line in Owned state 426 // (dirty, but not writable), is responding and thus 427 // transferring the dirty line from one branch of the 428 // cache hierarchy to another 429 430 // send out an express snoop and invalidate all other 431 // copies (snooping a packet that needs writable is the 432 // same as an invalidation), thus turning the Owned line 433 // into a Modified line, note that we don't invalidate the 434 // block in the current cache or any other cache on the 435 // path to memory 436 437 // create a downstream express snoop with cleared packet 438 // flags, there is no need to allocate any data as the 439 // packet is merely used to co-ordinate state transitions 440 Packet *snoop_pkt = new Packet(pkt, true, false); 441 442 // also reset the bus time that the original packet has 443 // not yet paid for 444 snoop_pkt->headerDelay = snoop_pkt->payloadDelay = 0; 445 446 // make this an instantaneous express snoop, and let the 447 // other caches in the system know that the another cache 448 // is responding, because we have found the authorative 449 // copy (Modified or Owned) that will supply the right 450 // data 451 snoop_pkt->setExpressSnoop(); 452 snoop_pkt->setCacheResponding(); 453 454 // this express snoop travels towards the memory, and at 455 // every crossbar it is snooped upwards thus reaching 456 // every cache in the system 457 bool M5_VAR_USED success = memSidePort.sendTimingReq(snoop_pkt); 458 // express snoops always succeed 459 assert(success); 460 461 // main memory will delete the snoop packet 462 463 // queue for deletion, as opposed to immediate deletion, as 464 // the sending cache is still relying on the packet 465 pendingDelete.reset(pkt); 466 467 // no need to take any further action in this particular cache 468 // as an upstram cache has already committed to responding, 469 // and we have already sent out any express snoops in the 470 // section above to ensure all other copies in the system are 471 // invalidated 472 return; 473 } 474 475 BaseCache::recvTimingReq(pkt); 476} 477 478PacketPtr 479Cache::createMissPacket(PacketPtr cpu_pkt, CacheBlk *blk, 480 bool needsWritable) const 481{ 482 // should never see evictions here 483 assert(!cpu_pkt->isEviction()); 484 485 bool blkValid = blk && blk->isValid(); 486 487 if (cpu_pkt->req->isUncacheable() || 488 (!blkValid && cpu_pkt->isUpgrade()) || 489 cpu_pkt->cmd == MemCmd::InvalidateReq || cpu_pkt->isClean()) { 490 // uncacheable requests and upgrades from upper-level caches 491 // that missed completely just go through as is 492 return nullptr; 493 } 494 495 assert(cpu_pkt->needsResponse()); 496 497 MemCmd cmd; 498 // @TODO make useUpgrades a parameter. 499 // Note that ownership protocols require upgrade, otherwise a 500 // write miss on a shared owned block will generate a ReadExcl, 501 // which will clobber the owned copy. 502 const bool useUpgrades = true; 503 if (cpu_pkt->cmd == MemCmd::WriteLineReq) { 504 assert(!blkValid || !blk->isWritable()); 505 // forward as invalidate to all other caches, this gives us 506 // the line in Exclusive state, and invalidates all other 507 // copies 508 cmd = MemCmd::InvalidateReq; 509 } else if (blkValid && useUpgrades) { 510 // only reason to be here is that blk is read only and we need 511 // it to be writable 512 assert(needsWritable); 513 assert(!blk->isWritable()); 514 cmd = cpu_pkt->isLLSC() ? MemCmd::SCUpgradeReq : MemCmd::UpgradeReq; 515 } else if (cpu_pkt->cmd == MemCmd::SCUpgradeFailReq || 516 cpu_pkt->cmd == MemCmd::StoreCondFailReq) { 517 // Even though this SC will fail, we still need to send out the 518 // request and get the data to supply it to other snoopers in the case 519 // where the determination the StoreCond fails is delayed due to 520 // all caches not being on the same local bus. 521 cmd = MemCmd::SCUpgradeFailReq; 522 } else { 523 // block is invalid 524 525 // If the request does not need a writable there are two cases 526 // where we need to ensure the response will not fetch the 527 // block in dirty state: 528 // * this cache is read only and it does not perform 529 // writebacks, 530 // * this cache is mostly exclusive and will not fill (since 531 // it does not fill it will have to writeback the dirty data 532 // immediately which generates uneccesary writebacks). 533 bool force_clean_rsp = isReadOnly || clusivity == Enums::mostly_excl; 534 cmd = needsWritable ? MemCmd::ReadExReq : 535 (force_clean_rsp ? MemCmd::ReadCleanReq : MemCmd::ReadSharedReq); 536 } 537 PacketPtr pkt = new Packet(cpu_pkt->req, cmd, blkSize); 538 539 // if there are upstream caches that have already marked the 540 // packet as having sharers (not passing writable), pass that info 541 // downstream 542 if (cpu_pkt->hasSharers() && !needsWritable) { 543 // note that cpu_pkt may have spent a considerable time in the 544 // MSHR queue and that the information could possibly be out 545 // of date, however, there is no harm in conservatively 546 // assuming the block has sharers 547 pkt->setHasSharers(); 548 DPRINTF(Cache, "%s: passing hasSharers from %s to %s\n", 549 __func__, cpu_pkt->print(), pkt->print()); 550 } 551 552 // the packet should be block aligned 553 assert(pkt->getAddr() == pkt->getBlockAddr(blkSize)); 554 555 pkt->allocate(); 556 DPRINTF(Cache, "%s: created %s from %s\n", __func__, pkt->print(), 557 cpu_pkt->print()); 558 return pkt; 559} 560 561 562Cycles 563Cache::handleAtomicReqMiss(PacketPtr pkt, CacheBlk *&blk, 564 PacketList &writebacks) 565{ 566 // deal with the packets that go through the write path of 567 // the cache, i.e. any evictions and writes 568 if (pkt->isEviction() || pkt->cmd == MemCmd::WriteClean || 569 (pkt->req->isUncacheable() && pkt->isWrite())) { 570 Cycles latency = ticksToCycles(memSidePort.sendAtomic(pkt)); 571 572 // at this point, if the request was an uncacheable write 573 // request, it has been satisfied by a memory below and the 574 // packet carries the response back 575 assert(!(pkt->req->isUncacheable() && pkt->isWrite()) || 576 pkt->isResponse()); 577 578 return latency; 579 } 580 581 // only misses left 582 583 PacketPtr bus_pkt = createMissPacket(pkt, blk, pkt->needsWritable()); 584 585 bool is_forward = (bus_pkt == nullptr); 586 587 if (is_forward) { 588 // just forwarding the same request to the next level 589 // no local cache operation involved 590 bus_pkt = pkt; 591 } 592 593 DPRINTF(Cache, "%s: Sending an atomic %s\n", __func__, 594 bus_pkt->print()); 595 596#if TRACING_ON 597 CacheBlk::State old_state = blk ? blk->status : 0; 598#endif 599 600 Cycles latency = ticksToCycles(memSidePort.sendAtomic(bus_pkt)); 601 602 bool is_invalidate = bus_pkt->isInvalidate(); 603 604 // We are now dealing with the response handling 605 DPRINTF(Cache, "%s: Receive response: %s in state %i\n", __func__, 606 bus_pkt->print(), old_state); 607 608 // If packet was a forward, the response (if any) is already 609 // in place in the bus_pkt == pkt structure, so we don't need 610 // to do anything. Otherwise, use the separate bus_pkt to 611 // generate response to pkt and then delete it. 612 if (!is_forward) { 613 if (pkt->needsResponse()) { 614 assert(bus_pkt->isResponse()); 615 if (bus_pkt->isError()) { 616 pkt->makeAtomicResponse(); 617 pkt->copyError(bus_pkt); 618 } else if (pkt->cmd == MemCmd::WriteLineReq) { 619 // note the use of pkt, not bus_pkt here. 620 621 // write-line request to the cache that promoted 622 // the write to a whole line 623 blk = handleFill(pkt, blk, writebacks, 624 allocOnFill(pkt->cmd)); 625 assert(blk != NULL); 626 is_invalidate = false; 627 satisfyRequest(pkt, blk); 628 } else if (bus_pkt->isRead() || 629 bus_pkt->cmd == MemCmd::UpgradeResp) { 630 // we're updating cache state to allow us to 631 // satisfy the upstream request from the cache 632 blk = handleFill(bus_pkt, blk, writebacks, 633 allocOnFill(pkt->cmd)); 634 satisfyRequest(pkt, blk); 635 maintainClusivity(pkt->fromCache(), blk); 636 } else { 637 // we're satisfying the upstream request without 638 // modifying cache state, e.g., a write-through 639 pkt->makeAtomicResponse(); 640 } 641 } 642 delete bus_pkt; 643 } 644 645 if (is_invalidate && blk && blk->isValid()) { 646 invalidateBlock(blk); 647 } 648 649 return latency; 650} 651 652Tick 653Cache::recvAtomic(PacketPtr pkt) 654{ 655 promoteWholeLineWrites(pkt); 656 657 return BaseCache::recvAtomic(pkt); 658} 659 660 661///////////////////////////////////////////////////// 662// 663// Response handling: responses from the memory side 664// 665///////////////////////////////////////////////////// 666 667 668void 669Cache::serviceMSHRTargets(MSHR *mshr, const PacketPtr pkt, CacheBlk *blk, 670 PacketList &writebacks) 671{ 672 MSHR::Target *initial_tgt = mshr->getTarget(); 673 // First offset for critical word first calculations 674 const int initial_offset = initial_tgt->pkt->getOffset(blkSize); 675 676 const bool is_error = pkt->isError(); 677 // allow invalidation responses originating from write-line 678 // requests to be discarded 679 bool is_invalidate = pkt->isInvalidate(); 680 681 MSHR::TargetList targets = mshr->extractServiceableTargets(pkt); 682 for (auto &target: targets) { 683 Packet *tgt_pkt = target.pkt; 684 switch (target.source) { 685 case MSHR::Target::FromCPU: 686 Tick completion_time; 687 // Here we charge on completion_time the delay of the xbar if the 688 // packet comes from it, charged on headerDelay. 689 completion_time = pkt->headerDelay; 690 691 // Software prefetch handling for cache closest to core 692 if (tgt_pkt->cmd.isSWPrefetch()) { 693 // a software prefetch would have already been ack'd 694 // immediately with dummy data so the core would be able to 695 // retire it. This request completes right here, so we 696 // deallocate it. 697 delete tgt_pkt; 698 break; // skip response 699 } 700 701 // unlike the other packet flows, where data is found in other 702 // caches or memory and brought back, write-line requests always 703 // have the data right away, so the above check for "is fill?" 704 // cannot actually be determined until examining the stored MSHR 705 // state. We "catch up" with that logic here, which is duplicated 706 // from above. 707 if (tgt_pkt->cmd == MemCmd::WriteLineReq) { 708 assert(!is_error); 709 // we got the block in a writable state, so promote 710 // any deferred targets if possible 711 mshr->promoteWritable(); 712 // NB: we use the original packet here and not the response! 713 blk = handleFill(tgt_pkt, blk, writebacks, 714 targets.allocOnFill); 715 assert(blk); 716 717 // discard the invalidation response 718 is_invalidate = false; 719 } 720 721 if (blk && blk->isValid() && !mshr->isForward) { 722 satisfyRequest(tgt_pkt, blk, true, mshr->hasPostDowngrade()); 723 724 // How many bytes past the first request is this one 725 int transfer_offset = 726 tgt_pkt->getOffset(blkSize) - initial_offset; 727 if (transfer_offset < 0) { 728 transfer_offset += blkSize; 729 } 730 731 // If not critical word (offset) return payloadDelay. 732 // responseLatency is the latency of the return path 733 // from lower level caches/memory to an upper level cache or 734 // the core. 735 completion_time += clockEdge(responseLatency) + 736 (transfer_offset ? pkt->payloadDelay : 0); 737 738 assert(!tgt_pkt->req->isUncacheable()); 739 740 assert(tgt_pkt->req->masterId() < system->maxMasters()); 741 missLatency[tgt_pkt->cmdToIndex()][tgt_pkt->req->masterId()] += 742 completion_time - target.recvTime; 743 } else if (pkt->cmd == MemCmd::UpgradeFailResp) { 744 // failed StoreCond upgrade 745 assert(tgt_pkt->cmd == MemCmd::StoreCondReq || 746 tgt_pkt->cmd == MemCmd::StoreCondFailReq || 747 tgt_pkt->cmd == MemCmd::SCUpgradeFailReq); 748 // responseLatency is the latency of the return path 749 // from lower level caches/memory to an upper level cache or 750 // the core. 751 completion_time += clockEdge(responseLatency) + 752 pkt->payloadDelay; 753 tgt_pkt->req->setExtraData(0); 754 } else { 755 // We are about to send a response to a cache above 756 // that asked for an invalidation; we need to 757 // invalidate our copy immediately as the most 758 // up-to-date copy of the block will now be in the 759 // cache above. It will also prevent this cache from 760 // responding (if the block was previously dirty) to 761 // snoops as they should snoop the caches above where 762 // they will get the response from. 763 if (is_invalidate && blk && blk->isValid()) { 764 invalidateBlock(blk); 765 } 766 // not a cache fill, just forwarding response 767 // responseLatency is the latency of the return path 768 // from lower level cahces/memory to the core. 769 completion_time += clockEdge(responseLatency) + 770 pkt->payloadDelay; 771 if (pkt->isRead() && !is_error) { 772 // sanity check 773 assert(pkt->getAddr() == tgt_pkt->getAddr()); 774 assert(pkt->getSize() >= tgt_pkt->getSize()); 775 776 tgt_pkt->setData(pkt->getConstPtr<uint8_t>()); 777 } 778 } 779 tgt_pkt->makeTimingResponse(); 780 // if this packet is an error copy that to the new packet 781 if (is_error) 782 tgt_pkt->copyError(pkt); 783 if (tgt_pkt->cmd == MemCmd::ReadResp && 784 (is_invalidate || mshr->hasPostInvalidate())) { 785 // If intermediate cache got ReadRespWithInvalidate, 786 // propagate that. Response should not have 787 // isInvalidate() set otherwise. 788 tgt_pkt->cmd = MemCmd::ReadRespWithInvalidate; 789 DPRINTF(Cache, "%s: updated cmd to %s\n", __func__, 790 tgt_pkt->print()); 791 } 792 // Reset the bus additional time as it is now accounted for 793 tgt_pkt->headerDelay = tgt_pkt->payloadDelay = 0; 794 cpuSidePort.schedTimingResp(tgt_pkt, completion_time, true); 795 break; 796 797 case MSHR::Target::FromPrefetcher: 798 assert(tgt_pkt->cmd == MemCmd::HardPFReq); 799 if (blk) 800 blk->status |= BlkHWPrefetched; 801 delete tgt_pkt; 802 break; 803 804 case MSHR::Target::FromSnoop: 805 // I don't believe that a snoop can be in an error state 806 assert(!is_error); 807 // response to snoop request 808 DPRINTF(Cache, "processing deferred snoop...\n"); 809 // If the response is invalidating, a snooping target can 810 // be satisfied if it is also invalidating. If the reponse is, not 811 // only invalidating, but more specifically an InvalidateResp and 812 // the MSHR was created due to an InvalidateReq then a cache above 813 // is waiting to satisfy a WriteLineReq. In this case even an 814 // non-invalidating snoop is added as a target here since this is 815 // the ordering point. When the InvalidateResp reaches this cache, 816 // the snooping target will snoop further the cache above with the 817 // WriteLineReq. 818 assert(!is_invalidate || pkt->cmd == MemCmd::InvalidateResp || 819 pkt->req->isCacheMaintenance() || 820 mshr->hasPostInvalidate()); 821 handleSnoop(tgt_pkt, blk, true, true, mshr->hasPostInvalidate()); 822 break; 823 824 default: 825 panic("Illegal target->source enum %d\n", target.source); 826 } 827 } 828 829 maintainClusivity(targets.hasFromCache, blk); 830 831 if (blk && blk->isValid()) { 832 // an invalidate response stemming from a write line request 833 // should not invalidate the block, so check if the 834 // invalidation should be discarded 835 if (is_invalidate || mshr->hasPostInvalidate()) { 836 invalidateBlock(blk); 837 } else if (mshr->hasPostDowngrade()) { 838 blk->status &= ~BlkWritable; 839 } 840 } 841} 842 843PacketPtr 844Cache::evictBlock(CacheBlk *blk) 845{ 846 PacketPtr pkt = (blk->isDirty() || writebackClean) ? 847 writebackBlk(blk) : cleanEvictBlk(blk); 848 849 invalidateBlock(blk); 850 851 return pkt; 852} 853 854void 855Cache::evictBlock(CacheBlk *blk, PacketList &writebacks) 856{ 857 PacketPtr pkt = evictBlock(blk); 858 if (pkt) { 859 writebacks.push_back(pkt); 860 } 861} 862 863PacketPtr 864Cache::cleanEvictBlk(CacheBlk *blk) 865{ 866 assert(!writebackClean); 867 assert(blk && blk->isValid() && !blk->isDirty()); 868 869 // Creating a zero sized write, a message to the snoop filter 870 RequestPtr req = std::make_shared<Request>( 871 regenerateBlkAddr(blk), blkSize, 0, Request::wbMasterId); 872 873 if (blk->isSecure()) 874 req->setFlags(Request::SECURE); 875 876 req->taskId(blk->task_id); 877 878 PacketPtr pkt = new Packet(req, MemCmd::CleanEvict); 879 pkt->allocate(); 880 DPRINTF(Cache, "Create CleanEvict %s\n", pkt->print()); 881 882 return pkt; 883} 884 885///////////////////////////////////////////////////// 886// 887// Snoop path: requests coming in from the memory side 888// 889///////////////////////////////////////////////////// 890 891void 892Cache::doTimingSupplyResponse(PacketPtr req_pkt, const uint8_t *blk_data, 893 bool already_copied, bool pending_inval) 894{ 895 // sanity check 896 assert(req_pkt->isRequest()); 897 assert(req_pkt->needsResponse()); 898 899 DPRINTF(Cache, "%s: for %s\n", __func__, req_pkt->print()); 900 // timing-mode snoop responses require a new packet, unless we 901 // already made a copy... 902 PacketPtr pkt = req_pkt; 903 if (!already_copied) 904 // do not clear flags, and allocate space for data if the 905 // packet needs it (the only packets that carry data are read 906 // responses) 907 pkt = new Packet(req_pkt, false, req_pkt->isRead()); 908 909 assert(req_pkt->req->isUncacheable() || req_pkt->isInvalidate() || 910 pkt->hasSharers()); 911 pkt->makeTimingResponse(); 912 if (pkt->isRead()) { 913 pkt->setDataFromBlock(blk_data, blkSize); 914 } 915 if (pkt->cmd == MemCmd::ReadResp && pending_inval) { 916 // Assume we defer a response to a read from a far-away cache 917 // A, then later defer a ReadExcl from a cache B on the same 918 // bus as us. We'll assert cacheResponding in both cases, but 919 // in the latter case cacheResponding will keep the 920 // invalidation from reaching cache A. This special response 921 // tells cache A that it gets the block to satisfy its read, 922 // but must immediately invalidate it. 923 pkt->cmd = MemCmd::ReadRespWithInvalidate; 924 } 925 // Here we consider forward_time, paying for just forward latency and 926 // also charging the delay provided by the xbar. 927 // forward_time is used as send_time in next allocateWriteBuffer(). 928 Tick forward_time = clockEdge(forwardLatency) + pkt->headerDelay; 929 // Here we reset the timing of the packet. 930 pkt->headerDelay = pkt->payloadDelay = 0; 931 DPRINTF(CacheVerbose, "%s: created response: %s tick: %lu\n", __func__, 932 pkt->print(), forward_time); 933 memSidePort.schedTimingSnoopResp(pkt, forward_time, true); 934} 935 936uint32_t 937Cache::handleSnoop(PacketPtr pkt, CacheBlk *blk, bool is_timing, 938 bool is_deferred, bool pending_inval) 939{ 940 DPRINTF(CacheVerbose, "%s: for %s\n", __func__, pkt->print()); 941 // deferred snoops can only happen in timing mode 942 assert(!(is_deferred && !is_timing)); 943 // pending_inval only makes sense on deferred snoops 944 assert(!(pending_inval && !is_deferred)); 945 assert(pkt->isRequest()); 946 947 // the packet may get modified if we or a forwarded snooper 948 // responds in atomic mode, so remember a few things about the 949 // original packet up front 950 bool invalidate = pkt->isInvalidate(); 951 bool M5_VAR_USED needs_writable = pkt->needsWritable(); 952 953 // at the moment we could get an uncacheable write which does not 954 // have the invalidate flag, and we need a suitable way of dealing 955 // with this case 956 panic_if(invalidate && pkt->req->isUncacheable(), 957 "%s got an invalidating uncacheable snoop request %s", 958 name(), pkt->print()); 959 960 uint32_t snoop_delay = 0; 961 962 if (forwardSnoops) { 963 // first propagate snoop upward to see if anyone above us wants to 964 // handle it. save & restore packet src since it will get 965 // rewritten to be relative to cpu-side bus (if any) 966 bool alreadyResponded = pkt->cacheResponding(); 967 if (is_timing) { 968 // copy the packet so that we can clear any flags before 969 // forwarding it upwards, we also allocate data (passing 970 // the pointer along in case of static data), in case 971 // there is a snoop hit in upper levels 972 Packet snoopPkt(pkt, true, true); 973 snoopPkt.setExpressSnoop(); 974 // the snoop packet does not need to wait any additional 975 // time 976 snoopPkt.headerDelay = snoopPkt.payloadDelay = 0; 977 cpuSidePort.sendTimingSnoopReq(&snoopPkt); 978 979 // add the header delay (including crossbar and snoop 980 // delays) of the upward snoop to the snoop delay for this 981 // cache 982 snoop_delay += snoopPkt.headerDelay; 983 984 if (snoopPkt.cacheResponding()) { 985 // cache-to-cache response from some upper cache 986 assert(!alreadyResponded); 987 pkt->setCacheResponding(); 988 } 989 // upstream cache has the block, or has an outstanding 990 // MSHR, pass the flag on 991 if (snoopPkt.hasSharers()) { 992 pkt->setHasSharers(); 993 } 994 // If this request is a prefetch or clean evict and an upper level 995 // signals block present, make sure to propagate the block 996 // presence to the requester. 997 if (snoopPkt.isBlockCached()) { 998 pkt->setBlockCached(); 999 } 1000 // If the request was satisfied by snooping the cache 1001 // above, mark the original packet as satisfied too. 1002 if (snoopPkt.satisfied()) { 1003 pkt->setSatisfied(); 1004 } 1005 } else { 1006 cpuSidePort.sendAtomicSnoop(pkt); 1007 if (!alreadyResponded && pkt->cacheResponding()) { 1008 // cache-to-cache response from some upper cache: 1009 // forward response to original requester 1010 assert(pkt->isResponse()); 1011 } 1012 } 1013 } 1014 1015 bool respond = false; 1016 bool blk_valid = blk && blk->isValid(); 1017 if (pkt->isClean()) { 1018 if (blk_valid && blk->isDirty()) { 1019 DPRINTF(CacheVerbose, "%s: packet (snoop) %s found block: %s\n", 1020 __func__, pkt->print(), blk->print()); 1021 PacketPtr wb_pkt = writecleanBlk(blk, pkt->req->getDest(), pkt->id); 1022 PacketList writebacks; 1023 writebacks.push_back(wb_pkt); 1024 1025 if (is_timing) { 1026 // anything that is merely forwarded pays for the forward 1027 // latency and the delay provided by the crossbar 1028 Tick forward_time = clockEdge(forwardLatency) + 1029 pkt->headerDelay; 1030 doWritebacks(writebacks, forward_time); 1031 } else { 1032 doWritebacksAtomic(writebacks); 1033 } 1034 pkt->setSatisfied(); 1035 } 1036 } else if (!blk_valid) { 1037 DPRINTF(CacheVerbose, "%s: snoop miss for %s\n", __func__, 1038 pkt->print()); 1039 if (is_deferred) { 1040 // we no longer have the block, and will not respond, but a 1041 // packet was allocated in MSHR::handleSnoop and we have 1042 // to delete it 1043 assert(pkt->needsResponse()); 1044 1045 // we have passed the block to a cache upstream, that 1046 // cache should be responding 1047 assert(pkt->cacheResponding()); 1048 1049 delete pkt; 1050 } 1051 return snoop_delay; 1052 } else { 1053 DPRINTF(Cache, "%s: snoop hit for %s, old state is %s\n", __func__, 1054 pkt->print(), blk->print()); 1055 1056 // We may end up modifying both the block state and the packet (if 1057 // we respond in atomic mode), so just figure out what to do now 1058 // and then do it later. We respond to all snoops that need 1059 // responses provided we have the block in dirty state. The 1060 // invalidation itself is taken care of below. We don't respond to 1061 // cache maintenance operations as this is done by the destination 1062 // xbar. 1063 respond = blk->isDirty() && pkt->needsResponse(); 1064 1065 chatty_assert(!(isReadOnly && blk->isDirty()), "Should never have " 1066 "a dirty block in a read-only cache %s\n", name()); 1067 } 1068 1069 // Invalidate any prefetch's from below that would strip write permissions 1070 // MemCmd::HardPFReq is only observed by upstream caches. After missing 1071 // above and in it's own cache, a new MemCmd::ReadReq is created that 1072 // downstream caches observe. 1073 if (pkt->mustCheckAbove()) { 1074 DPRINTF(Cache, "Found addr %#llx in upper level cache for snoop %s " 1075 "from lower cache\n", pkt->getAddr(), pkt->print()); 1076 pkt->setBlockCached(); 1077 return snoop_delay; 1078 } 1079 1080 if (pkt->isRead() && !invalidate) { 1081 // reading without requiring the line in a writable state 1082 assert(!needs_writable); 1083 pkt->setHasSharers(); 1084 1085 // if the requesting packet is uncacheable, retain the line in 1086 // the current state, otherwhise unset the writable flag, 1087 // which means we go from Modified to Owned (and will respond 1088 // below), remain in Owned (and will respond below), from 1089 // Exclusive to Shared, or remain in Shared 1090 if (!pkt->req->isUncacheable()) 1091 blk->status &= ~BlkWritable; 1092 DPRINTF(Cache, "new state is %s\n", blk->print()); 1093 } 1094 1095 if (respond) { 1096 // prevent anyone else from responding, cache as well as 1097 // memory, and also prevent any memory from even seeing the 1098 // request 1099 pkt->setCacheResponding(); 1100 if (!pkt->isClean() && blk->isWritable()) { 1101 // inform the cache hierarchy that this cache had the line 1102 // in the Modified state so that we avoid unnecessary 1103 // invalidations (see Packet::setResponderHadWritable) 1104 pkt->setResponderHadWritable(); 1105 1106 // in the case of an uncacheable request there is no point 1107 // in setting the responderHadWritable flag, but since the 1108 // recipient does not care there is no harm in doing so 1109 } else { 1110 // if the packet has needsWritable set we invalidate our 1111 // copy below and all other copies will be invalidates 1112 // through express snoops, and if needsWritable is not set 1113 // we already called setHasSharers above 1114 } 1115 1116 // if we are returning a writable and dirty (Modified) line, 1117 // we should be invalidating the line 1118 panic_if(!invalidate && !pkt->hasSharers(), 1119 "%s is passing a Modified line through %s, " 1120 "but keeping the block", name(), pkt->print()); 1121 1122 if (is_timing) { 1123 doTimingSupplyResponse(pkt, blk->data, is_deferred, pending_inval); 1124 } else { 1125 pkt->makeAtomicResponse(); 1126 // packets such as upgrades do not actually have any data 1127 // payload 1128 if (pkt->hasData()) 1129 pkt->setDataFromBlock(blk->data, blkSize); 1130 } 1131 } 1132 1133 if (!respond && is_deferred) { 1134 assert(pkt->needsResponse()); 1135 delete pkt; 1136 } 1137 1138 // Do this last in case it deallocates block data or something 1139 // like that 1140 if (blk_valid && invalidate) { 1141 invalidateBlock(blk); 1142 DPRINTF(Cache, "new state is %s\n", blk->print()); 1143 } 1144 1145 return snoop_delay; 1146} 1147 1148 1149void 1150Cache::recvTimingSnoopReq(PacketPtr pkt) 1151{ 1152 DPRINTF(CacheVerbose, "%s: for %s\n", __func__, pkt->print()); 1153 1154 // no need to snoop requests that are not in range 1155 if (!inRange(pkt->getAddr())) { 1156 return; 1157 } 1158 1159 bool is_secure = pkt->isSecure(); 1160 CacheBlk *blk = tags->findBlock(pkt->getAddr(), is_secure); 1161 1162 Addr blk_addr = pkt->getBlockAddr(blkSize); 1163 MSHR *mshr = mshrQueue.findMatch(blk_addr, is_secure); 1164 1165 // Update the latency cost of the snoop so that the crossbar can 1166 // account for it. Do not overwrite what other neighbouring caches 1167 // have already done, rather take the maximum. The update is 1168 // tentative, for cases where we return before an upward snoop 1169 // happens below. 1170 pkt->snoopDelay = std::max<uint32_t>(pkt->snoopDelay, 1171 lookupLatency * clockPeriod()); 1172 1173 // Inform request(Prefetch, CleanEvict or Writeback) from below of 1174 // MSHR hit, set setBlockCached. 1175 if (mshr && pkt->mustCheckAbove()) { 1176 DPRINTF(Cache, "Setting block cached for %s from lower cache on " 1177 "mshr hit\n", pkt->print()); 1178 pkt->setBlockCached(); 1179 return; 1180 } 1181 1182 // Bypass any existing cache maintenance requests if the request 1183 // has been satisfied already (i.e., the dirty block has been 1184 // found). 1185 if (mshr && pkt->req->isCacheMaintenance() && pkt->satisfied()) { 1186 return; 1187 } 1188 1189 // Let the MSHR itself track the snoop and decide whether we want 1190 // to go ahead and do the regular cache snoop 1191 if (mshr && mshr->handleSnoop(pkt, order++)) { 1192 DPRINTF(Cache, "Deferring snoop on in-service MSHR to blk %#llx (%s)." 1193 "mshrs: %s\n", blk_addr, is_secure ? "s" : "ns", 1194 mshr->print()); 1195 1196 if (mshr->getNumTargets() > numTarget) 1197 warn("allocating bonus target for snoop"); //handle later 1198 return; 1199 } 1200 1201 //We also need to check the writeback buffers and handle those 1202 WriteQueueEntry *wb_entry = writeBuffer.findMatch(blk_addr, is_secure); 1203 if (wb_entry) { 1204 DPRINTF(Cache, "Snoop hit in writeback to addr %#llx (%s)\n", 1205 pkt->getAddr(), is_secure ? "s" : "ns"); 1206 // Expect to see only Writebacks and/or CleanEvicts here, both of 1207 // which should not be generated for uncacheable data. 1208 assert(!wb_entry->isUncacheable()); 1209 // There should only be a single request responsible for generating 1210 // Writebacks/CleanEvicts. 1211 assert(wb_entry->getNumTargets() == 1); 1212 PacketPtr wb_pkt = wb_entry->getTarget()->pkt; 1213 assert(wb_pkt->isEviction() || wb_pkt->cmd == MemCmd::WriteClean); 1214 1215 if (pkt->isEviction()) { 1216 // if the block is found in the write queue, set the BLOCK_CACHED 1217 // flag for Writeback/CleanEvict snoop. On return the snoop will 1218 // propagate the BLOCK_CACHED flag in Writeback packets and prevent 1219 // any CleanEvicts from travelling down the memory hierarchy. 1220 pkt->setBlockCached(); 1221 DPRINTF(Cache, "%s: Squashing %s from lower cache on writequeue " 1222 "hit\n", __func__, pkt->print()); 1223 return; 1224 } 1225 1226 // conceptually writebacks are no different to other blocks in 1227 // this cache, so the behaviour is modelled after handleSnoop, 1228 // the difference being that instead of querying the block 1229 // state to determine if it is dirty and writable, we use the 1230 // command and fields of the writeback packet 1231 bool respond = wb_pkt->cmd == MemCmd::WritebackDirty && 1232 pkt->needsResponse(); 1233 bool have_writable = !wb_pkt->hasSharers(); 1234 bool invalidate = pkt->isInvalidate(); 1235 1236 if (!pkt->req->isUncacheable() && pkt->isRead() && !invalidate) { 1237 assert(!pkt->needsWritable()); 1238 pkt->setHasSharers(); 1239 wb_pkt->setHasSharers(); 1240 } 1241 1242 if (respond) { 1243 pkt->setCacheResponding(); 1244 1245 if (have_writable) { 1246 pkt->setResponderHadWritable(); 1247 } 1248 1249 doTimingSupplyResponse(pkt, wb_pkt->getConstPtr<uint8_t>(), 1250 false, false); 1251 } 1252 1253 if (invalidate && wb_pkt->cmd != MemCmd::WriteClean) { 1254 // Invalidation trumps our writeback... discard here 1255 // Note: markInService will remove entry from writeback buffer. 1256 markInService(wb_entry); 1257 delete wb_pkt; 1258 } 1259 } 1260 1261 // If this was a shared writeback, there may still be 1262 // other shared copies above that require invalidation. 1263 // We could be more selective and return here if the 1264 // request is non-exclusive or if the writeback is 1265 // exclusive. 1266 uint32_t snoop_delay = handleSnoop(pkt, blk, true, false, false); 1267 1268 // Override what we did when we first saw the snoop, as we now 1269 // also have the cost of the upwards snoops to account for 1270 pkt->snoopDelay = std::max<uint32_t>(pkt->snoopDelay, snoop_delay + 1271 lookupLatency * clockPeriod()); 1272} 1273 1274Tick 1275Cache::recvAtomicSnoop(PacketPtr pkt) 1276{ 1277 // no need to snoop requests that are not in range. 1278 if (!inRange(pkt->getAddr())) { 1279 return 0; 1280 } 1281 1282 CacheBlk *blk = tags->findBlock(pkt->getAddr(), pkt->isSecure()); 1283 uint32_t snoop_delay = handleSnoop(pkt, blk, false, false, false); 1284 return snoop_delay + lookupLatency * clockPeriod(); 1285} 1286 1287bool 1288Cache::isCachedAbove(PacketPtr pkt, bool is_timing) 1289{ 1290 if (!forwardSnoops) 1291 return false; 1292 // Mirroring the flow of HardPFReqs, the cache sends CleanEvict and 1293 // Writeback snoops into upper level caches to check for copies of the 1294 // same block. Using the BLOCK_CACHED flag with the Writeback/CleanEvict 1295 // packet, the cache can inform the crossbar below of presence or absence 1296 // of the block. 1297 if (is_timing) { 1298 Packet snoop_pkt(pkt, true, false); 1299 snoop_pkt.setExpressSnoop(); 1300 // Assert that packet is either Writeback or CleanEvict and not a 1301 // prefetch request because prefetch requests need an MSHR and may 1302 // generate a snoop response. 1303 assert(pkt->isEviction() || pkt->cmd == MemCmd::WriteClean); 1304 snoop_pkt.senderState = nullptr; 1305 cpuSidePort.sendTimingSnoopReq(&snoop_pkt); 1306 // Writeback/CleanEvict snoops do not generate a snoop response. 1307 assert(!(snoop_pkt.cacheResponding())); 1308 return snoop_pkt.isBlockCached(); 1309 } else { 1310 cpuSidePort.sendAtomicSnoop(pkt); 1311 return pkt->isBlockCached(); 1312 } 1313} 1314 1315bool 1316Cache::sendMSHRQueuePacket(MSHR* mshr) 1317{ 1318 assert(mshr); 1319 1320 // use request from 1st target 1321 PacketPtr tgt_pkt = mshr->getTarget()->pkt; 1322 1323 if (tgt_pkt->cmd == MemCmd::HardPFReq && forwardSnoops) { 1324 DPRINTF(Cache, "%s: MSHR %s\n", __func__, tgt_pkt->print()); 1325 1326 // we should never have hardware prefetches to allocated 1327 // blocks 1328 assert(!tags->findBlock(mshr->blkAddr, mshr->isSecure)); 1329 1330 // We need to check the caches above us to verify that 1331 // they don't have a copy of this block in the dirty state 1332 // at the moment. Without this check we could get a stale 1333 // copy from memory that might get used in place of the 1334 // dirty one. 1335 Packet snoop_pkt(tgt_pkt, true, false); 1336 snoop_pkt.setExpressSnoop(); 1337 // We are sending this packet upwards, but if it hits we will 1338 // get a snoop response that we end up treating just like a 1339 // normal response, hence it needs the MSHR as its sender 1340 // state 1341 snoop_pkt.senderState = mshr; 1342 cpuSidePort.sendTimingSnoopReq(&snoop_pkt); 1343 1344 // Check to see if the prefetch was squashed by an upper cache (to 1345 // prevent us from grabbing the line) or if a Check to see if a 1346 // writeback arrived between the time the prefetch was placed in 1347 // the MSHRs and when it was selected to be sent or if the 1348 // prefetch was squashed by an upper cache. 1349 1350 // It is important to check cacheResponding before 1351 // prefetchSquashed. If another cache has committed to 1352 // responding, it will be sending a dirty response which will 1353 // arrive at the MSHR allocated for this request. Checking the 1354 // prefetchSquash first may result in the MSHR being 1355 // prematurely deallocated. 1356 if (snoop_pkt.cacheResponding()) { 1357 auto M5_VAR_USED r = outstandingSnoop.insert(snoop_pkt.req); 1358 assert(r.second); 1359 1360 // if we are getting a snoop response with no sharers it 1361 // will be allocated as Modified 1362 bool pending_modified_resp = !snoop_pkt.hasSharers(); 1363 markInService(mshr, pending_modified_resp); 1364 1365 DPRINTF(Cache, "Upward snoop of prefetch for addr" 1366 " %#x (%s) hit\n", 1367 tgt_pkt->getAddr(), tgt_pkt->isSecure()? "s": "ns"); 1368 return false; 1369 } 1370 1371 if (snoop_pkt.isBlockCached()) { 1372 DPRINTF(Cache, "Block present, prefetch squashed by cache. " 1373 "Deallocating mshr target %#x.\n", 1374 mshr->blkAddr); 1375 1376 // Deallocate the mshr target 1377 if (mshrQueue.forceDeallocateTarget(mshr)) { 1378 // Clear block if this deallocation resulted freed an 1379 // mshr when all had previously been utilized 1380 clearBlocked(Blocked_NoMSHRs); 1381 } 1382 1383 // given that no response is expected, delete Request and Packet 1384 delete tgt_pkt; 1385 1386 return false; 1387 } 1388 } 1389 1390 return BaseCache::sendMSHRQueuePacket(mshr); 1391} 1392 1393Cache* 1394CacheParams::create() 1395{ 1396 assert(tags); 1397 assert(replacement_policy); 1398 1399 return new Cache(this); 1400} 1401