cache.cc revision 12724
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 assert(pkt->isResponse()); 275 assert(!system->bypassCaches()); 276 277 // determine if the response is from a snoop request we created 278 // (in which case it should be in the outstandingSnoop), or if we 279 // merely forwarded someone else's snoop request 280 const bool forwardAsSnoop = outstandingSnoop.find(pkt->req) == 281 outstandingSnoop.end(); 282 283 if (!forwardAsSnoop) { 284 // the packet came from this cache, so sink it here and do not 285 // forward it 286 assert(pkt->cmd == MemCmd::HardPFResp); 287 288 outstandingSnoop.erase(pkt->req); 289 290 DPRINTF(Cache, "Got prefetch response from above for addr " 291 "%#llx (%s)\n", pkt->getAddr(), pkt->isSecure() ? "s" : "ns"); 292 recvTimingResp(pkt); 293 return; 294 } 295 296 // forwardLatency is set here because there is a response from an 297 // upper level cache. 298 // To pay the delay that occurs if the packet comes from the bus, 299 // we charge also headerDelay. 300 Tick snoop_resp_time = clockEdge(forwardLatency) + pkt->headerDelay; 301 // Reset the timing of the packet. 302 pkt->headerDelay = pkt->payloadDelay = 0; 303 memSidePort.schedTimingSnoopResp(pkt, snoop_resp_time); 304} 305 306void 307Cache::promoteWholeLineWrites(PacketPtr pkt) 308{ 309 // Cache line clearing instructions 310 if (doFastWrites && (pkt->cmd == MemCmd::WriteReq) && 311 (pkt->getSize() == blkSize) && (pkt->getOffset(blkSize) == 0)) { 312 pkt->cmd = MemCmd::WriteLineReq; 313 DPRINTF(Cache, "packet promoted from Write to WriteLineReq\n"); 314 } 315} 316 317void 318Cache::handleTimingReqHit(PacketPtr pkt, CacheBlk *blk, Tick request_time) 319{ 320 // should never be satisfying an uncacheable access as we 321 // flush and invalidate any existing block as part of the 322 // lookup 323 assert(!pkt->req->isUncacheable()); 324 325 BaseCache::handleTimingReqHit(pkt, blk, request_time); 326} 327 328void 329Cache::handleTimingReqMiss(PacketPtr pkt, CacheBlk *blk, Tick forward_time, 330 Tick request_time) 331{ 332 if (pkt->req->isUncacheable()) { 333 // ignore any existing MSHR if we are dealing with an 334 // uncacheable request 335 336 // should have flushed and have no valid block 337 assert(!blk || !blk->isValid()); 338 339 mshr_uncacheable[pkt->cmdToIndex()][pkt->req->masterId()]++; 340 341 if (pkt->isWrite()) { 342 allocateWriteBuffer(pkt, forward_time); 343 } else { 344 assert(pkt->isRead()); 345 346 // uncacheable accesses always allocate a new MSHR 347 348 // Here we are using forward_time, modelling the latency of 349 // a miss (outbound) just as forwardLatency, neglecting the 350 // lookupLatency component. 351 allocateMissBuffer(pkt, forward_time); 352 } 353 354 return; 355 } 356 357 Addr blk_addr = pkt->getBlockAddr(blkSize); 358 359 MSHR *mshr = mshrQueue.findMatch(blk_addr, pkt->isSecure()); 360 361 // Software prefetch handling: 362 // To keep the core from waiting on data it won't look at 363 // anyway, send back a response with dummy data. Miss handling 364 // will continue asynchronously. Unfortunately, the core will 365 // insist upon freeing original Packet/Request, so we have to 366 // create a new pair with a different lifecycle. Note that this 367 // processing happens before any MSHR munging on the behalf of 368 // this request because this new Request will be the one stored 369 // into the MSHRs, not the original. 370 if (pkt->cmd.isSWPrefetch()) { 371 assert(pkt->needsResponse()); 372 assert(pkt->req->hasPaddr()); 373 assert(!pkt->req->isUncacheable()); 374 375 // There's no reason to add a prefetch as an additional target 376 // to an existing MSHR. If an outstanding request is already 377 // in progress, there is nothing for the prefetch to do. 378 // If this is the case, we don't even create a request at all. 379 PacketPtr pf = nullptr; 380 381 if (!mshr) { 382 // copy the request and create a new SoftPFReq packet 383 RequestPtr req = new Request(pkt->req->getPaddr(), 384 pkt->req->getSize(), 385 pkt->req->getFlags(), 386 pkt->req->masterId()); 387 pf = new Packet(req, pkt->cmd); 388 pf->allocate(); 389 assert(pf->getAddr() == pkt->getAddr()); 390 assert(pf->getSize() == pkt->getSize()); 391 } 392 393 pkt->makeTimingResponse(); 394 395 // request_time is used here, taking into account lat and the delay 396 // charged if the packet comes from the xbar. 397 cpuSidePort.schedTimingResp(pkt, request_time, true); 398 399 // If an outstanding request is in progress (we found an 400 // MSHR) this is set to null 401 pkt = pf; 402 } 403 404 BaseCache::handleTimingReqMiss(pkt, mshr, blk, forward_time, request_time); 405} 406 407void 408Cache::recvTimingReq(PacketPtr pkt) 409{ 410 DPRINTF(CacheTags, "%s tags:\n%s\n", __func__, tags->print()); 411 412 assert(pkt->isRequest()); 413 414 // Just forward the packet if caches are disabled. 415 if (system->bypassCaches()) { 416 // @todo This should really enqueue the packet rather 417 bool M5_VAR_USED success = memSidePort.sendTimingReq(pkt); 418 assert(success); 419 return; 420 } 421 422 promoteWholeLineWrites(pkt); 423 424 if (pkt->cacheResponding()) { 425 // a cache above us (but not where the packet came from) is 426 // responding to the request, in other words it has the line 427 // in Modified or Owned state 428 DPRINTF(Cache, "Cache above responding to %s: not responding\n", 429 pkt->print()); 430 431 // if the packet needs the block to be writable, and the cache 432 // that has promised to respond (setting the cache responding 433 // flag) is not providing writable (it is in Owned rather than 434 // the Modified state), we know that there may be other Shared 435 // copies in the system; go out and invalidate them all 436 assert(pkt->needsWritable() && !pkt->responderHadWritable()); 437 438 // an upstream cache that had the line in Owned state 439 // (dirty, but not writable), is responding and thus 440 // transferring the dirty line from one branch of the 441 // cache hierarchy to another 442 443 // send out an express snoop and invalidate all other 444 // copies (snooping a packet that needs writable is the 445 // same as an invalidation), thus turning the Owned line 446 // into a Modified line, note that we don't invalidate the 447 // block in the current cache or any other cache on the 448 // path to memory 449 450 // create a downstream express snoop with cleared packet 451 // flags, there is no need to allocate any data as the 452 // packet is merely used to co-ordinate state transitions 453 Packet *snoop_pkt = new Packet(pkt, true, false); 454 455 // also reset the bus time that the original packet has 456 // not yet paid for 457 snoop_pkt->headerDelay = snoop_pkt->payloadDelay = 0; 458 459 // make this an instantaneous express snoop, and let the 460 // other caches in the system know that the another cache 461 // is responding, because we have found the authorative 462 // copy (Modified or Owned) that will supply the right 463 // data 464 snoop_pkt->setExpressSnoop(); 465 snoop_pkt->setCacheResponding(); 466 467 // this express snoop travels towards the memory, and at 468 // every crossbar it is snooped upwards thus reaching 469 // every cache in the system 470 bool M5_VAR_USED success = memSidePort.sendTimingReq(snoop_pkt); 471 // express snoops always succeed 472 assert(success); 473 474 // main memory will delete the snoop packet 475 476 // queue for deletion, as opposed to immediate deletion, as 477 // the sending cache is still relying on the packet 478 pendingDelete.reset(pkt); 479 480 // no need to take any further action in this particular cache 481 // as an upstram cache has already committed to responding, 482 // and we have already sent out any express snoops in the 483 // section above to ensure all other copies in the system are 484 // invalidated 485 return; 486 } 487 488 BaseCache::recvTimingReq(pkt); 489} 490 491PacketPtr 492Cache::createMissPacket(PacketPtr cpu_pkt, CacheBlk *blk, 493 bool needsWritable) const 494{ 495 // should never see evictions here 496 assert(!cpu_pkt->isEviction()); 497 498 bool blkValid = blk && blk->isValid(); 499 500 if (cpu_pkt->req->isUncacheable() || 501 (!blkValid && cpu_pkt->isUpgrade()) || 502 cpu_pkt->cmd == MemCmd::InvalidateReq || cpu_pkt->isClean()) { 503 // uncacheable requests and upgrades from upper-level caches 504 // that missed completely just go through as is 505 return nullptr; 506 } 507 508 assert(cpu_pkt->needsResponse()); 509 510 MemCmd cmd; 511 // @TODO make useUpgrades a parameter. 512 // Note that ownership protocols require upgrade, otherwise a 513 // write miss on a shared owned block will generate a ReadExcl, 514 // which will clobber the owned copy. 515 const bool useUpgrades = true; 516 if (cpu_pkt->cmd == MemCmd::WriteLineReq) { 517 assert(!blkValid || !blk->isWritable()); 518 // forward as invalidate to all other caches, this gives us 519 // the line in Exclusive state, and invalidates all other 520 // copies 521 cmd = MemCmd::InvalidateReq; 522 } else if (blkValid && useUpgrades) { 523 // only reason to be here is that blk is read only and we need 524 // it to be writable 525 assert(needsWritable); 526 assert(!blk->isWritable()); 527 cmd = cpu_pkt->isLLSC() ? MemCmd::SCUpgradeReq : MemCmd::UpgradeReq; 528 } else if (cpu_pkt->cmd == MemCmd::SCUpgradeFailReq || 529 cpu_pkt->cmd == MemCmd::StoreCondFailReq) { 530 // Even though this SC will fail, we still need to send out the 531 // request and get the data to supply it to other snoopers in the case 532 // where the determination the StoreCond fails is delayed due to 533 // all caches not being on the same local bus. 534 cmd = MemCmd::SCUpgradeFailReq; 535 } else { 536 // block is invalid 537 538 // If the request does not need a writable there are two cases 539 // where we need to ensure the response will not fetch the 540 // block in dirty state: 541 // * this cache is read only and it does not perform 542 // writebacks, 543 // * this cache is mostly exclusive and will not fill (since 544 // it does not fill it will have to writeback the dirty data 545 // immediately which generates uneccesary writebacks). 546 bool force_clean_rsp = isReadOnly || clusivity == Enums::mostly_excl; 547 cmd = needsWritable ? MemCmd::ReadExReq : 548 (force_clean_rsp ? MemCmd::ReadCleanReq : MemCmd::ReadSharedReq); 549 } 550 PacketPtr pkt = new Packet(cpu_pkt->req, cmd, blkSize); 551 552 // if there are upstream caches that have already marked the 553 // packet as having sharers (not passing writable), pass that info 554 // downstream 555 if (cpu_pkt->hasSharers() && !needsWritable) { 556 // note that cpu_pkt may have spent a considerable time in the 557 // MSHR queue and that the information could possibly be out 558 // of date, however, there is no harm in conservatively 559 // assuming the block has sharers 560 pkt->setHasSharers(); 561 DPRINTF(Cache, "%s: passing hasSharers from %s to %s\n", 562 __func__, cpu_pkt->print(), pkt->print()); 563 } 564 565 // the packet should be block aligned 566 assert(pkt->getAddr() == pkt->getBlockAddr(blkSize)); 567 568 pkt->allocate(); 569 DPRINTF(Cache, "%s: created %s from %s\n", __func__, pkt->print(), 570 cpu_pkt->print()); 571 return pkt; 572} 573 574 575Cycles 576Cache::handleAtomicReqMiss(PacketPtr pkt, CacheBlk *blk, 577 PacketList &writebacks) 578{ 579 // deal with the packets that go through the write path of 580 // the cache, i.e. any evictions and writes 581 if (pkt->isEviction() || pkt->cmd == MemCmd::WriteClean || 582 (pkt->req->isUncacheable() && pkt->isWrite())) { 583 Cycles latency = ticksToCycles(memSidePort.sendAtomic(pkt)); 584 585 // at this point, if the request was an uncacheable write 586 // request, it has been satisfied by a memory below and the 587 // packet carries the response back 588 assert(!(pkt->req->isUncacheable() && pkt->isWrite()) || 589 pkt->isResponse()); 590 591 return latency; 592 } 593 594 // only misses left 595 596 PacketPtr bus_pkt = createMissPacket(pkt, blk, pkt->needsWritable()); 597 598 bool is_forward = (bus_pkt == nullptr); 599 600 if (is_forward) { 601 // just forwarding the same request to the next level 602 // no local cache operation involved 603 bus_pkt = pkt; 604 } 605 606 DPRINTF(Cache, "%s: Sending an atomic %s\n", __func__, 607 bus_pkt->print()); 608 609#if TRACING_ON 610 CacheBlk::State old_state = blk ? blk->status : 0; 611#endif 612 613 Cycles latency = ticksToCycles(memSidePort.sendAtomic(bus_pkt)); 614 615 bool is_invalidate = bus_pkt->isInvalidate(); 616 617 // We are now dealing with the response handling 618 DPRINTF(Cache, "%s: Receive response: %s in state %i\n", __func__, 619 bus_pkt->print(), old_state); 620 621 // If packet was a forward, the response (if any) is already 622 // in place in the bus_pkt == pkt structure, so we don't need 623 // to do anything. Otherwise, use the separate bus_pkt to 624 // generate response to pkt and then delete it. 625 if (!is_forward) { 626 if (pkt->needsResponse()) { 627 assert(bus_pkt->isResponse()); 628 if (bus_pkt->isError()) { 629 pkt->makeAtomicResponse(); 630 pkt->copyError(bus_pkt); 631 } else if (pkt->cmd == MemCmd::WriteLineReq) { 632 // note the use of pkt, not bus_pkt here. 633 634 // write-line request to the cache that promoted 635 // the write to a whole line 636 blk = handleFill(pkt, blk, writebacks, 637 allocOnFill(pkt->cmd)); 638 assert(blk != NULL); 639 is_invalidate = false; 640 satisfyRequest(pkt, blk); 641 } else if (bus_pkt->isRead() || 642 bus_pkt->cmd == MemCmd::UpgradeResp) { 643 // we're updating cache state to allow us to 644 // satisfy the upstream request from the cache 645 blk = handleFill(bus_pkt, blk, writebacks, 646 allocOnFill(pkt->cmd)); 647 satisfyRequest(pkt, blk); 648 maintainClusivity(pkt->fromCache(), blk); 649 } else { 650 // we're satisfying the upstream request without 651 // modifying cache state, e.g., a write-through 652 pkt->makeAtomicResponse(); 653 } 654 } 655 delete bus_pkt; 656 } 657 658 if (is_invalidate && blk && blk->isValid()) { 659 invalidateBlock(blk); 660 } 661 662 return latency; 663} 664 665Tick 666Cache::recvAtomic(PacketPtr pkt) 667{ 668 // Forward the request if the system is in cache bypass mode. 669 if (system->bypassCaches()) 670 return ticksToCycles(memSidePort.sendAtomic(pkt)); 671 672 promoteWholeLineWrites(pkt); 673 674 return BaseCache::recvAtomic(pkt); 675} 676 677 678///////////////////////////////////////////////////// 679// 680// Response handling: responses from the memory side 681// 682///////////////////////////////////////////////////// 683 684 685void 686Cache::serviceMSHRTargets(MSHR *mshr, const PacketPtr pkt, CacheBlk *blk, 687 PacketList &writebacks) 688{ 689 MSHR::Target *initial_tgt = mshr->getTarget(); 690 // First offset for critical word first calculations 691 const int initial_offset = initial_tgt->pkt->getOffset(blkSize); 692 693 const bool is_error = pkt->isError(); 694 bool is_fill = !mshr->isForward && 695 (pkt->isRead() || pkt->cmd == MemCmd::UpgradeResp); 696 // allow invalidation responses originating from write-line 697 // requests to be discarded 698 bool is_invalidate = pkt->isInvalidate(); 699 700 MSHR::TargetList targets = mshr->extractServiceableTargets(pkt); 701 for (auto &target: targets) { 702 Packet *tgt_pkt = target.pkt; 703 switch (target.source) { 704 case MSHR::Target::FromCPU: 705 Tick completion_time; 706 // Here we charge on completion_time the delay of the xbar if the 707 // packet comes from it, charged on headerDelay. 708 completion_time = pkt->headerDelay; 709 710 // Software prefetch handling for cache closest to core 711 if (tgt_pkt->cmd.isSWPrefetch()) { 712 // a software prefetch would have already been ack'd 713 // immediately with dummy data so the core would be able to 714 // retire it. This request completes right here, so we 715 // deallocate it. 716 delete tgt_pkt->req; 717 delete tgt_pkt; 718 break; // skip response 719 } 720 721 // unlike the other packet flows, where data is found in other 722 // caches or memory and brought back, write-line requests always 723 // have the data right away, so the above check for "is fill?" 724 // cannot actually be determined until examining the stored MSHR 725 // state. We "catch up" with that logic here, which is duplicated 726 // from above. 727 if (tgt_pkt->cmd == MemCmd::WriteLineReq) { 728 assert(!is_error); 729 // we got the block in a writable state, so promote 730 // any deferred targets if possible 731 mshr->promoteWritable(); 732 // NB: we use the original packet here and not the response! 733 blk = handleFill(tgt_pkt, blk, writebacks, 734 targets.allocOnFill); 735 assert(blk); 736 737 // treat as a fill, and discard the invalidation 738 // response 739 is_fill = true; 740 is_invalidate = false; 741 } 742 743 if (is_fill) { 744 satisfyRequest(tgt_pkt, blk, true, mshr->hasPostDowngrade()); 745 746 // How many bytes past the first request is this one 747 int transfer_offset = 748 tgt_pkt->getOffset(blkSize) - initial_offset; 749 if (transfer_offset < 0) { 750 transfer_offset += blkSize; 751 } 752 753 // If not critical word (offset) return payloadDelay. 754 // responseLatency is the latency of the return path 755 // from lower level caches/memory to an upper level cache or 756 // the core. 757 completion_time += clockEdge(responseLatency) + 758 (transfer_offset ? pkt->payloadDelay : 0); 759 760 assert(!tgt_pkt->req->isUncacheable()); 761 762 assert(tgt_pkt->req->masterId() < system->maxMasters()); 763 missLatency[tgt_pkt->cmdToIndex()][tgt_pkt->req->masterId()] += 764 completion_time - target.recvTime; 765 } else if (pkt->cmd == MemCmd::UpgradeFailResp) { 766 // failed StoreCond upgrade 767 assert(tgt_pkt->cmd == MemCmd::StoreCondReq || 768 tgt_pkt->cmd == MemCmd::StoreCondFailReq || 769 tgt_pkt->cmd == MemCmd::SCUpgradeFailReq); 770 // responseLatency is the latency of the return path 771 // from lower level caches/memory to an upper level cache or 772 // the core. 773 completion_time += clockEdge(responseLatency) + 774 pkt->payloadDelay; 775 tgt_pkt->req->setExtraData(0); 776 } else { 777 // We are about to send a response to a cache above 778 // that asked for an invalidation; we need to 779 // invalidate our copy immediately as the most 780 // up-to-date copy of the block will now be in the 781 // cache above. It will also prevent this cache from 782 // responding (if the block was previously dirty) to 783 // snoops as they should snoop the caches above where 784 // they will get the response from. 785 if (is_invalidate && blk && blk->isValid()) { 786 invalidateBlock(blk); 787 } 788 // not a cache fill, just forwarding response 789 // responseLatency is the latency of the return path 790 // from lower level cahces/memory to the core. 791 completion_time += clockEdge(responseLatency) + 792 pkt->payloadDelay; 793 if (pkt->isRead() && !is_error) { 794 // sanity check 795 assert(pkt->getAddr() == tgt_pkt->getAddr()); 796 assert(pkt->getSize() >= tgt_pkt->getSize()); 797 798 tgt_pkt->setData(pkt->getConstPtr<uint8_t>()); 799 } 800 } 801 tgt_pkt->makeTimingResponse(); 802 // if this packet is an error copy that to the new packet 803 if (is_error) 804 tgt_pkt->copyError(pkt); 805 if (tgt_pkt->cmd == MemCmd::ReadResp && 806 (is_invalidate || mshr->hasPostInvalidate())) { 807 // If intermediate cache got ReadRespWithInvalidate, 808 // propagate that. Response should not have 809 // isInvalidate() set otherwise. 810 tgt_pkt->cmd = MemCmd::ReadRespWithInvalidate; 811 DPRINTF(Cache, "%s: updated cmd to %s\n", __func__, 812 tgt_pkt->print()); 813 } 814 // Reset the bus additional time as it is now accounted for 815 tgt_pkt->headerDelay = tgt_pkt->payloadDelay = 0; 816 cpuSidePort.schedTimingResp(tgt_pkt, completion_time, true); 817 break; 818 819 case MSHR::Target::FromPrefetcher: 820 assert(tgt_pkt->cmd == MemCmd::HardPFReq); 821 if (blk) 822 blk->status |= BlkHWPrefetched; 823 delete tgt_pkt->req; 824 delete tgt_pkt; 825 break; 826 827 case MSHR::Target::FromSnoop: 828 // I don't believe that a snoop can be in an error state 829 assert(!is_error); 830 // response to snoop request 831 DPRINTF(Cache, "processing deferred snoop...\n"); 832 // If the response is invalidating, a snooping target can 833 // be satisfied if it is also invalidating. If the reponse is, not 834 // only invalidating, but more specifically an InvalidateResp and 835 // the MSHR was created due to an InvalidateReq then a cache above 836 // is waiting to satisfy a WriteLineReq. In this case even an 837 // non-invalidating snoop is added as a target here since this is 838 // the ordering point. When the InvalidateResp reaches this cache, 839 // the snooping target will snoop further the cache above with the 840 // WriteLineReq. 841 assert(!is_invalidate || pkt->cmd == MemCmd::InvalidateResp || 842 pkt->req->isCacheMaintenance() || 843 mshr->hasPostInvalidate()); 844 handleSnoop(tgt_pkt, blk, true, true, mshr->hasPostInvalidate()); 845 break; 846 847 default: 848 panic("Illegal target->source enum %d\n", target.source); 849 } 850 } 851 852 maintainClusivity(targets.hasFromCache, blk); 853 854 if (blk && blk->isValid()) { 855 // an invalidate response stemming from a write line request 856 // should not invalidate the block, so check if the 857 // invalidation should be discarded 858 if (is_invalidate || mshr->hasPostInvalidate()) { 859 invalidateBlock(blk); 860 } else if (mshr->hasPostDowngrade()) { 861 blk->status &= ~BlkWritable; 862 } 863 } 864} 865 866PacketPtr 867Cache::evictBlock(CacheBlk *blk) 868{ 869 PacketPtr pkt = (blk->isDirty() || writebackClean) ? 870 writebackBlk(blk) : cleanEvictBlk(blk); 871 872 invalidateBlock(blk); 873 874 return pkt; 875} 876 877void 878Cache::evictBlock(CacheBlk *blk, PacketList &writebacks) 879{ 880 PacketPtr pkt = evictBlock(blk); 881 if (pkt) { 882 writebacks.push_back(pkt); 883 } 884} 885 886PacketPtr 887Cache::cleanEvictBlk(CacheBlk *blk) 888{ 889 assert(!writebackClean); 890 assert(blk && blk->isValid() && !blk->isDirty()); 891 // Creating a zero sized write, a message to the snoop filter 892 Request *req = 893 new Request(tags->regenerateBlkAddr(blk), blkSize, 0, 894 Request::wbMasterId); 895 if (blk->isSecure()) 896 req->setFlags(Request::SECURE); 897 898 req->taskId(blk->task_id); 899 900 PacketPtr pkt = new Packet(req, MemCmd::CleanEvict); 901 pkt->allocate(); 902 DPRINTF(Cache, "Create CleanEvict %s\n", pkt->print()); 903 904 return pkt; 905} 906 907 908///////////////////////////////////////////////////// 909// 910// Snoop path: requests coming in from the memory side 911// 912///////////////////////////////////////////////////// 913 914void 915Cache::doTimingSupplyResponse(PacketPtr req_pkt, const uint8_t *blk_data, 916 bool already_copied, bool pending_inval) 917{ 918 // sanity check 919 assert(req_pkt->isRequest()); 920 assert(req_pkt->needsResponse()); 921 922 DPRINTF(Cache, "%s: for %s\n", __func__, req_pkt->print()); 923 // timing-mode snoop responses require a new packet, unless we 924 // already made a copy... 925 PacketPtr pkt = req_pkt; 926 if (!already_copied) 927 // do not clear flags, and allocate space for data if the 928 // packet needs it (the only packets that carry data are read 929 // responses) 930 pkt = new Packet(req_pkt, false, req_pkt->isRead()); 931 932 assert(req_pkt->req->isUncacheable() || req_pkt->isInvalidate() || 933 pkt->hasSharers()); 934 pkt->makeTimingResponse(); 935 if (pkt->isRead()) { 936 pkt->setDataFromBlock(blk_data, blkSize); 937 } 938 if (pkt->cmd == MemCmd::ReadResp && pending_inval) { 939 // Assume we defer a response to a read from a far-away cache 940 // A, then later defer a ReadExcl from a cache B on the same 941 // bus as us. We'll assert cacheResponding in both cases, but 942 // in the latter case cacheResponding will keep the 943 // invalidation from reaching cache A. This special response 944 // tells cache A that it gets the block to satisfy its read, 945 // but must immediately invalidate it. 946 pkt->cmd = MemCmd::ReadRespWithInvalidate; 947 } 948 // Here we consider forward_time, paying for just forward latency and 949 // also charging the delay provided by the xbar. 950 // forward_time is used as send_time in next allocateWriteBuffer(). 951 Tick forward_time = clockEdge(forwardLatency) + pkt->headerDelay; 952 // Here we reset the timing of the packet. 953 pkt->headerDelay = pkt->payloadDelay = 0; 954 DPRINTF(CacheVerbose, "%s: created response: %s tick: %lu\n", __func__, 955 pkt->print(), forward_time); 956 memSidePort.schedTimingSnoopResp(pkt, forward_time, true); 957} 958 959uint32_t 960Cache::handleSnoop(PacketPtr pkt, CacheBlk *blk, bool is_timing, 961 bool is_deferred, bool pending_inval) 962{ 963 DPRINTF(CacheVerbose, "%s: for %s\n", __func__, pkt->print()); 964 // deferred snoops can only happen in timing mode 965 assert(!(is_deferred && !is_timing)); 966 // pending_inval only makes sense on deferred snoops 967 assert(!(pending_inval && !is_deferred)); 968 assert(pkt->isRequest()); 969 970 // the packet may get modified if we or a forwarded snooper 971 // responds in atomic mode, so remember a few things about the 972 // original packet up front 973 bool invalidate = pkt->isInvalidate(); 974 bool M5_VAR_USED needs_writable = pkt->needsWritable(); 975 976 // at the moment we could get an uncacheable write which does not 977 // have the invalidate flag, and we need a suitable way of dealing 978 // with this case 979 panic_if(invalidate && pkt->req->isUncacheable(), 980 "%s got an invalidating uncacheable snoop request %s", 981 name(), pkt->print()); 982 983 uint32_t snoop_delay = 0; 984 985 if (forwardSnoops) { 986 // first propagate snoop upward to see if anyone above us wants to 987 // handle it. save & restore packet src since it will get 988 // rewritten to be relative to cpu-side bus (if any) 989 bool alreadyResponded = pkt->cacheResponding(); 990 if (is_timing) { 991 // copy the packet so that we can clear any flags before 992 // forwarding it upwards, we also allocate data (passing 993 // the pointer along in case of static data), in case 994 // there is a snoop hit in upper levels 995 Packet snoopPkt(pkt, true, true); 996 snoopPkt.setExpressSnoop(); 997 // the snoop packet does not need to wait any additional 998 // time 999 snoopPkt.headerDelay = snoopPkt.payloadDelay = 0; 1000 cpuSidePort.sendTimingSnoopReq(&snoopPkt); 1001 1002 // add the header delay (including crossbar and snoop 1003 // delays) of the upward snoop to the snoop delay for this 1004 // cache 1005 snoop_delay += snoopPkt.headerDelay; 1006 1007 if (snoopPkt.cacheResponding()) { 1008 // cache-to-cache response from some upper cache 1009 assert(!alreadyResponded); 1010 pkt->setCacheResponding(); 1011 } 1012 // upstream cache has the block, or has an outstanding 1013 // MSHR, pass the flag on 1014 if (snoopPkt.hasSharers()) { 1015 pkt->setHasSharers(); 1016 } 1017 // If this request is a prefetch or clean evict and an upper level 1018 // signals block present, make sure to propagate the block 1019 // presence to the requester. 1020 if (snoopPkt.isBlockCached()) { 1021 pkt->setBlockCached(); 1022 } 1023 // If the request was satisfied by snooping the cache 1024 // above, mark the original packet as satisfied too. 1025 if (snoopPkt.satisfied()) { 1026 pkt->setSatisfied(); 1027 } 1028 } else { 1029 cpuSidePort.sendAtomicSnoop(pkt); 1030 if (!alreadyResponded && pkt->cacheResponding()) { 1031 // cache-to-cache response from some upper cache: 1032 // forward response to original requester 1033 assert(pkt->isResponse()); 1034 } 1035 } 1036 } 1037 1038 bool respond = false; 1039 bool blk_valid = blk && blk->isValid(); 1040 if (pkt->isClean()) { 1041 if (blk_valid && blk->isDirty()) { 1042 DPRINTF(CacheVerbose, "%s: packet (snoop) %s found block: %s\n", 1043 __func__, pkt->print(), blk->print()); 1044 PacketPtr wb_pkt = writecleanBlk(blk, pkt->req->getDest(), pkt->id); 1045 PacketList writebacks; 1046 writebacks.push_back(wb_pkt); 1047 1048 if (is_timing) { 1049 // anything that is merely forwarded pays for the forward 1050 // latency and the delay provided by the crossbar 1051 Tick forward_time = clockEdge(forwardLatency) + 1052 pkt->headerDelay; 1053 doWritebacks(writebacks, forward_time); 1054 } else { 1055 doWritebacksAtomic(writebacks); 1056 } 1057 pkt->setSatisfied(); 1058 } 1059 } else if (!blk_valid) { 1060 DPRINTF(CacheVerbose, "%s: snoop miss for %s\n", __func__, 1061 pkt->print()); 1062 if (is_deferred) { 1063 // we no longer have the block, and will not respond, but a 1064 // packet was allocated in MSHR::handleSnoop and we have 1065 // to delete it 1066 assert(pkt->needsResponse()); 1067 1068 // we have passed the block to a cache upstream, that 1069 // cache should be responding 1070 assert(pkt->cacheResponding()); 1071 1072 delete pkt; 1073 } 1074 return snoop_delay; 1075 } else { 1076 DPRINTF(Cache, "%s: snoop hit for %s, old state is %s\n", __func__, 1077 pkt->print(), blk->print()); 1078 1079 // We may end up modifying both the block state and the packet (if 1080 // we respond in atomic mode), so just figure out what to do now 1081 // and then do it later. We respond to all snoops that need 1082 // responses provided we have the block in dirty state. The 1083 // invalidation itself is taken care of below. We don't respond to 1084 // cache maintenance operations as this is done by the destination 1085 // xbar. 1086 respond = blk->isDirty() && pkt->needsResponse(); 1087 1088 chatty_assert(!(isReadOnly && blk->isDirty()), "Should never have " 1089 "a dirty block in a read-only cache %s\n", name()); 1090 } 1091 1092 // Invalidate any prefetch's from below that would strip write permissions 1093 // MemCmd::HardPFReq is only observed by upstream caches. After missing 1094 // above and in it's own cache, a new MemCmd::ReadReq is created that 1095 // downstream caches observe. 1096 if (pkt->mustCheckAbove()) { 1097 DPRINTF(Cache, "Found addr %#llx in upper level cache for snoop %s " 1098 "from lower cache\n", pkt->getAddr(), pkt->print()); 1099 pkt->setBlockCached(); 1100 return snoop_delay; 1101 } 1102 1103 if (pkt->isRead() && !invalidate) { 1104 // reading without requiring the line in a writable state 1105 assert(!needs_writable); 1106 pkt->setHasSharers(); 1107 1108 // if the requesting packet is uncacheable, retain the line in 1109 // the current state, otherwhise unset the writable flag, 1110 // which means we go from Modified to Owned (and will respond 1111 // below), remain in Owned (and will respond below), from 1112 // Exclusive to Shared, or remain in Shared 1113 if (!pkt->req->isUncacheable()) 1114 blk->status &= ~BlkWritable; 1115 DPRINTF(Cache, "new state is %s\n", blk->print()); 1116 } 1117 1118 if (respond) { 1119 // prevent anyone else from responding, cache as well as 1120 // memory, and also prevent any memory from even seeing the 1121 // request 1122 pkt->setCacheResponding(); 1123 if (!pkt->isClean() && blk->isWritable()) { 1124 // inform the cache hierarchy that this cache had the line 1125 // in the Modified state so that we avoid unnecessary 1126 // invalidations (see Packet::setResponderHadWritable) 1127 pkt->setResponderHadWritable(); 1128 1129 // in the case of an uncacheable request there is no point 1130 // in setting the responderHadWritable flag, but since the 1131 // recipient does not care there is no harm in doing so 1132 } else { 1133 // if the packet has needsWritable set we invalidate our 1134 // copy below and all other copies will be invalidates 1135 // through express snoops, and if needsWritable is not set 1136 // we already called setHasSharers above 1137 } 1138 1139 // if we are returning a writable and dirty (Modified) line, 1140 // we should be invalidating the line 1141 panic_if(!invalidate && !pkt->hasSharers(), 1142 "%s is passing a Modified line through %s, " 1143 "but keeping the block", name(), pkt->print()); 1144 1145 if (is_timing) { 1146 doTimingSupplyResponse(pkt, blk->data, is_deferred, pending_inval); 1147 } else { 1148 pkt->makeAtomicResponse(); 1149 // packets such as upgrades do not actually have any data 1150 // payload 1151 if (pkt->hasData()) 1152 pkt->setDataFromBlock(blk->data, blkSize); 1153 } 1154 } 1155 1156 if (!respond && is_deferred) { 1157 assert(pkt->needsResponse()); 1158 1159 // if we copied the deferred packet with the intention to 1160 // respond, but are not responding, then a cache above us must 1161 // be, and we can use this as the indication of whether this 1162 // is a packet where we created a copy of the request or not 1163 if (!pkt->cacheResponding()) { 1164 delete pkt->req; 1165 } 1166 1167 delete pkt; 1168 } 1169 1170 // Do this last in case it deallocates block data or something 1171 // like that 1172 if (blk_valid && invalidate) { 1173 invalidateBlock(blk); 1174 DPRINTF(Cache, "new state is %s\n", blk->print()); 1175 } 1176 1177 return snoop_delay; 1178} 1179 1180 1181void 1182Cache::recvTimingSnoopReq(PacketPtr pkt) 1183{ 1184 DPRINTF(CacheVerbose, "%s: for %s\n", __func__, pkt->print()); 1185 1186 // Snoops shouldn't happen when bypassing caches 1187 assert(!system->bypassCaches()); 1188 1189 // no need to snoop requests that are not in range 1190 if (!inRange(pkt->getAddr())) { 1191 return; 1192 } 1193 1194 bool is_secure = pkt->isSecure(); 1195 CacheBlk *blk = tags->findBlock(pkt->getAddr(), is_secure); 1196 1197 Addr blk_addr = pkt->getBlockAddr(blkSize); 1198 MSHR *mshr = mshrQueue.findMatch(blk_addr, is_secure); 1199 1200 // Update the latency cost of the snoop so that the crossbar can 1201 // account for it. Do not overwrite what other neighbouring caches 1202 // have already done, rather take the maximum. The update is 1203 // tentative, for cases where we return before an upward snoop 1204 // happens below. 1205 pkt->snoopDelay = std::max<uint32_t>(pkt->snoopDelay, 1206 lookupLatency * clockPeriod()); 1207 1208 // Inform request(Prefetch, CleanEvict or Writeback) from below of 1209 // MSHR hit, set setBlockCached. 1210 if (mshr && pkt->mustCheckAbove()) { 1211 DPRINTF(Cache, "Setting block cached for %s from lower cache on " 1212 "mshr hit\n", pkt->print()); 1213 pkt->setBlockCached(); 1214 return; 1215 } 1216 1217 // Bypass any existing cache maintenance requests if the request 1218 // has been satisfied already (i.e., the dirty block has been 1219 // found). 1220 if (mshr && pkt->req->isCacheMaintenance() && pkt->satisfied()) { 1221 return; 1222 } 1223 1224 // Let the MSHR itself track the snoop and decide whether we want 1225 // to go ahead and do the regular cache snoop 1226 if (mshr && mshr->handleSnoop(pkt, order++)) { 1227 DPRINTF(Cache, "Deferring snoop on in-service MSHR to blk %#llx (%s)." 1228 "mshrs: %s\n", blk_addr, is_secure ? "s" : "ns", 1229 mshr->print()); 1230 1231 if (mshr->getNumTargets() > numTarget) 1232 warn("allocating bonus target for snoop"); //handle later 1233 return; 1234 } 1235 1236 //We also need to check the writeback buffers and handle those 1237 WriteQueueEntry *wb_entry = writeBuffer.findMatch(blk_addr, is_secure); 1238 if (wb_entry) { 1239 DPRINTF(Cache, "Snoop hit in writeback to addr %#llx (%s)\n", 1240 pkt->getAddr(), is_secure ? "s" : "ns"); 1241 // Expect to see only Writebacks and/or CleanEvicts here, both of 1242 // which should not be generated for uncacheable data. 1243 assert(!wb_entry->isUncacheable()); 1244 // There should only be a single request responsible for generating 1245 // Writebacks/CleanEvicts. 1246 assert(wb_entry->getNumTargets() == 1); 1247 PacketPtr wb_pkt = wb_entry->getTarget()->pkt; 1248 assert(wb_pkt->isEviction() || wb_pkt->cmd == MemCmd::WriteClean); 1249 1250 if (pkt->isEviction()) { 1251 // if the block is found in the write queue, set the BLOCK_CACHED 1252 // flag for Writeback/CleanEvict snoop. On return the snoop will 1253 // propagate the BLOCK_CACHED flag in Writeback packets and prevent 1254 // any CleanEvicts from travelling down the memory hierarchy. 1255 pkt->setBlockCached(); 1256 DPRINTF(Cache, "%s: Squashing %s from lower cache on writequeue " 1257 "hit\n", __func__, pkt->print()); 1258 return; 1259 } 1260 1261 // conceptually writebacks are no different to other blocks in 1262 // this cache, so the behaviour is modelled after handleSnoop, 1263 // the difference being that instead of querying the block 1264 // state to determine if it is dirty and writable, we use the 1265 // command and fields of the writeback packet 1266 bool respond = wb_pkt->cmd == MemCmd::WritebackDirty && 1267 pkt->needsResponse(); 1268 bool have_writable = !wb_pkt->hasSharers(); 1269 bool invalidate = pkt->isInvalidate(); 1270 1271 if (!pkt->req->isUncacheable() && pkt->isRead() && !invalidate) { 1272 assert(!pkt->needsWritable()); 1273 pkt->setHasSharers(); 1274 wb_pkt->setHasSharers(); 1275 } 1276 1277 if (respond) { 1278 pkt->setCacheResponding(); 1279 1280 if (have_writable) { 1281 pkt->setResponderHadWritable(); 1282 } 1283 1284 doTimingSupplyResponse(pkt, wb_pkt->getConstPtr<uint8_t>(), 1285 false, false); 1286 } 1287 1288 if (invalidate && wb_pkt->cmd != MemCmd::WriteClean) { 1289 // Invalidation trumps our writeback... discard here 1290 // Note: markInService will remove entry from writeback buffer. 1291 markInService(wb_entry); 1292 delete wb_pkt; 1293 } 1294 } 1295 1296 // If this was a shared writeback, there may still be 1297 // other shared copies above that require invalidation. 1298 // We could be more selective and return here if the 1299 // request is non-exclusive or if the writeback is 1300 // exclusive. 1301 uint32_t snoop_delay = handleSnoop(pkt, blk, true, false, false); 1302 1303 // Override what we did when we first saw the snoop, as we now 1304 // also have the cost of the upwards snoops to account for 1305 pkt->snoopDelay = std::max<uint32_t>(pkt->snoopDelay, snoop_delay + 1306 lookupLatency * clockPeriod()); 1307} 1308 1309Tick 1310Cache::recvAtomicSnoop(PacketPtr pkt) 1311{ 1312 // Snoops shouldn't happen when bypassing caches 1313 assert(!system->bypassCaches()); 1314 1315 // no need to snoop requests that are not in range. 1316 if (!inRange(pkt->getAddr())) { 1317 return 0; 1318 } 1319 1320 CacheBlk *blk = tags->findBlock(pkt->getAddr(), pkt->isSecure()); 1321 uint32_t snoop_delay = handleSnoop(pkt, blk, false, false, false); 1322 return snoop_delay + lookupLatency * clockPeriod(); 1323} 1324 1325bool 1326Cache::isCachedAbove(PacketPtr pkt, bool is_timing) 1327{ 1328 if (!forwardSnoops) 1329 return false; 1330 // Mirroring the flow of HardPFReqs, the cache sends CleanEvict and 1331 // Writeback snoops into upper level caches to check for copies of the 1332 // same block. Using the BLOCK_CACHED flag with the Writeback/CleanEvict 1333 // packet, the cache can inform the crossbar below of presence or absence 1334 // of the block. 1335 if (is_timing) { 1336 Packet snoop_pkt(pkt, true, false); 1337 snoop_pkt.setExpressSnoop(); 1338 // Assert that packet is either Writeback or CleanEvict and not a 1339 // prefetch request because prefetch requests need an MSHR and may 1340 // generate a snoop response. 1341 assert(pkt->isEviction() || pkt->cmd == MemCmd::WriteClean); 1342 snoop_pkt.senderState = nullptr; 1343 cpuSidePort.sendTimingSnoopReq(&snoop_pkt); 1344 // Writeback/CleanEvict snoops do not generate a snoop response. 1345 assert(!(snoop_pkt.cacheResponding())); 1346 return snoop_pkt.isBlockCached(); 1347 } else { 1348 cpuSidePort.sendAtomicSnoop(pkt); 1349 return pkt->isBlockCached(); 1350 } 1351} 1352 1353bool 1354Cache::sendMSHRQueuePacket(MSHR* mshr) 1355{ 1356 assert(mshr); 1357 1358 // use request from 1st target 1359 PacketPtr tgt_pkt = mshr->getTarget()->pkt; 1360 1361 if (tgt_pkt->cmd == MemCmd::HardPFReq && forwardSnoops) { 1362 DPRINTF(Cache, "%s: MSHR %s\n", __func__, tgt_pkt->print()); 1363 1364 // we should never have hardware prefetches to allocated 1365 // blocks 1366 assert(!tags->findBlock(mshr->blkAddr, mshr->isSecure)); 1367 1368 // We need to check the caches above us to verify that 1369 // they don't have a copy of this block in the dirty state 1370 // at the moment. Without this check we could get a stale 1371 // copy from memory that might get used in place of the 1372 // dirty one. 1373 Packet snoop_pkt(tgt_pkt, true, false); 1374 snoop_pkt.setExpressSnoop(); 1375 // We are sending this packet upwards, but if it hits we will 1376 // get a snoop response that we end up treating just like a 1377 // normal response, hence it needs the MSHR as its sender 1378 // state 1379 snoop_pkt.senderState = mshr; 1380 cpuSidePort.sendTimingSnoopReq(&snoop_pkt); 1381 1382 // Check to see if the prefetch was squashed by an upper cache (to 1383 // prevent us from grabbing the line) or if a Check to see if a 1384 // writeback arrived between the time the prefetch was placed in 1385 // the MSHRs and when it was selected to be sent or if the 1386 // prefetch was squashed by an upper cache. 1387 1388 // It is important to check cacheResponding before 1389 // prefetchSquashed. If another cache has committed to 1390 // responding, it will be sending a dirty response which will 1391 // arrive at the MSHR allocated for this request. Checking the 1392 // prefetchSquash first may result in the MSHR being 1393 // prematurely deallocated. 1394 if (snoop_pkt.cacheResponding()) { 1395 auto M5_VAR_USED r = outstandingSnoop.insert(snoop_pkt.req); 1396 assert(r.second); 1397 1398 // if we are getting a snoop response with no sharers it 1399 // will be allocated as Modified 1400 bool pending_modified_resp = !snoop_pkt.hasSharers(); 1401 markInService(mshr, pending_modified_resp); 1402 1403 DPRINTF(Cache, "Upward snoop of prefetch for addr" 1404 " %#x (%s) hit\n", 1405 tgt_pkt->getAddr(), tgt_pkt->isSecure()? "s": "ns"); 1406 return false; 1407 } 1408 1409 if (snoop_pkt.isBlockCached()) { 1410 DPRINTF(Cache, "Block present, prefetch squashed by cache. " 1411 "Deallocating mshr target %#x.\n", 1412 mshr->blkAddr); 1413 1414 // Deallocate the mshr target 1415 if (mshrQueue.forceDeallocateTarget(mshr)) { 1416 // Clear block if this deallocation resulted freed an 1417 // mshr when all had previously been utilized 1418 clearBlocked(Blocked_NoMSHRs); 1419 } 1420 1421 // given that no response is expected, delete Request and Packet 1422 delete tgt_pkt->req; 1423 delete tgt_pkt; 1424 1425 return false; 1426 } 1427 } 1428 1429 return BaseCache::sendMSHRQueuePacket(mshr); 1430} 1431 1432Cache* 1433CacheParams::create() 1434{ 1435 assert(tags); 1436 assert(replacement_policy); 1437 1438 return new Cache(this); 1439} 1440