src/mem/cache/mshr.cc

   1 /*
   2  * Copyright (c) 2012-2013, 2015 ARM Limited
   3  * All rights reserved.
   4  *
   5  * The license below extends only to copyright in the software and shall
   6  * not be construed as granting a license to any other intellectual
   7  * property including but not limited to intellectual property relating
   8  * to a hardware implementation of the functionality of the software
   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 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  */
  44
  45 /**
  46  * @file
  47  * Miss Status and Handling Register (MSHR) definitions.
  48  */
  49
  50 #include <algorithm>
  51 #include <cassert>
  52 #include <string>
  53 #include <vector>
  54
  55 #include "base/misc.hh"
  56 #include "base/types.hh"
  57 #include "debug/Cache.hh"
  58 #include "mem/cache/cache.hh"
  59 #include "mem/cache/mshr.hh"
  60 #include "sim/core.hh"
  61
  62 using namespace std;
  63
  64 MSHR::MSHR() : readyTime(0), _isUncacheable(false), downstreamPending(false),
  65                pendingDirty(false),
  66                postInvalidate(false), postDowngrade(false),
  67                queue(NULL), order(0), blkAddr(0),
  68                blkSize(0), isSecure(false), inService(false),
  69                isForward(false), threadNum(InvalidThreadID), data(NULL)
  70 {
  71 }
  72
  73
  74 MSHR::TargetList::TargetList()
  75     : needsExclusive(false), hasUpgrade(false)
  76 {}
  77
  78
  79 inline void
  80 MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
  81                       Counter order, Target::Source source, bool markPending)
  82 {
  83     if (source != Target::FromSnoop) {
  84         if (pkt->needsExclusive()) {
  85             needsExclusive = true;
  86         }
  87
  88         // StoreCondReq is effectively an upgrade if it's in an MSHR
  89         // since it would have been failed already if we didn't have a
  90         // read-only copy
  91         if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
  92             hasUpgrade = true;
  93         }
  94     }
  95
  96     if (markPending) {
  97         // Iterate over the SenderState stack and see if we find
  98         // an MSHR entry. If we do, set the downstreamPending
  99         // flag. Otherwise, do nothing.
 100         MSHR *mshr = pkt->findNextSenderState<MSHR>();
 101         if (mshr != NULL) {
 102             assert(!mshr->downstreamPending);
 103             mshr->downstreamPending = true;
 104         }
 105     }
 106
 107     emplace_back(Target(pkt, readyTime, order, source, markPending));
 108 }
 109
 110
 111 static void
 112 replaceUpgrade(PacketPtr pkt)
 113 {
 114     if (pkt->cmd == MemCmd::UpgradeReq) {
 115         pkt->cmd = MemCmd::ReadExReq;
 116         DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
 117     } else if (pkt->cmd == MemCmd::SCUpgradeReq) {
 118         pkt->cmd = MemCmd::SCUpgradeFailReq;
 119         DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
 120     } else if (pkt->cmd == MemCmd::StoreCondReq) {
 121         pkt->cmd = MemCmd::StoreCondFailReq;
 122         DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
 123     }
 124 }
 125
 126
 127 void
 128 MSHR::TargetList::replaceUpgrades()
 129 {
 130     if (!hasUpgrade)
 131         return;
 132
 133     for (auto& t : *this) {
 134         replaceUpgrade(t.pkt);
 135     }
 136
 137     hasUpgrade = false;
 138 }
 139
 140
 141 void
 142 MSHR::TargetList::clearDownstreamPending()
 143 {
 144     for (auto& t : *this) {
 145         if (t.markedPending) {
 146             // Iterate over the SenderState stack and see if we find
 147             // an MSHR entry. If we find one, clear the
 148             // downstreamPending flag by calling
 149             // clearDownstreamPending(). This recursively clears the
 150             // downstreamPending flag in all caches this packet has
 151             // passed through.
 152             MSHR *mshr = t.pkt->findNextSenderState<MSHR>();
 153             if (mshr != NULL) {
 154                 mshr->clearDownstreamPending();
 155             }
 156         }
 157     }
 158 }
 159
 160
 161 bool
 162 MSHR::TargetList::checkFunctional(PacketPtr pkt)
 163 {
 164     for (auto& t : *this) {
 165         if (pkt->checkFunctional(t.pkt)) {
 166             return true;
 167         }
 168     }
 169
 170     return false;
 171 }
 172
 173
 174 void
 175 MSHR::TargetList::print(std::ostream &os, int verbosity,
 176                         const std::string &prefix) const
 177 {
 178     for (auto& t : *this) {
 179         const char *s;
 180         switch (t.source) {
 181           case Target::FromCPU:
 182             s = "FromCPU";
 183             break;
 184           case Target::FromSnoop:
 185             s = "FromSnoop";
 186             break;
 187           case Target::FromPrefetcher:
 188             s = "FromPrefetcher";
 189             break;
 190           default:
 191             s = "";
 192             break;
 193         }
 194         ccprintf(os, "%s%s: ", prefix, s);
 195         t.pkt->print(os, verbosity, "");
 196     }
 197 }
 198
 199
 200 void
 201 MSHR::allocate(Addr blk_addr, unsigned blk_size, PacketPtr target,
 202                Tick when_ready, Counter _order)
 203 {
 204     blkAddr = blk_addr;
 205     blkSize = blk_size;
 206     isSecure = target->isSecure();
 207     readyTime = when_ready;
 208     order = _order;
 209     assert(target);
 210     isForward = false;
 211     _isUncacheable = target->req->isUncacheable();
 212     inService = false;
 213     downstreamPending = false;
 214     threadNum = 0;
 215     assert(targets.isReset());
 216     // Don't know of a case where we would allocate a new MSHR for a
 217     // snoop (mem-side request), so set source according to request here
 218     Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
 219         Target::FromPrefetcher : Target::FromCPU;
 220     targets.add(target, when_ready, _order, source, true);
 221     assert(deferredTargets.isReset());
 222     data = NULL;
 223 }
 224
 225
 226 void
 227 MSHR::clearDownstreamPending()
 228 {
 229     assert(downstreamPending);
 230     downstreamPending = false;
 231     // recursively clear flag on any MSHRs we will be forwarding
 232     // responses to
 233     targets.clearDownstreamPending();
 234 }
 235
 236 bool
 237 MSHR::markInService(bool pending_dirty_resp)
 238 {
 239     assert(!inService);
 240     if (isForwardNoResponse()) {
 241         // we just forwarded the request packet & don't expect a
 242         // response, so get rid of it
 243         assert(getNumTargets() == 1);
 244         popTarget();
 245         return true;
 246     }
 247
 248     inService = true;
 249     pendingDirty = targets.needsExclusive || pending_dirty_resp;
 250     postInvalidate = postDowngrade = false;
 251
 252     if (!downstreamPending) {
 253         // let upstream caches know that the request has made it to a
 254         // level where it's going to get a response
 255         targets.clearDownstreamPending();
 256     }
 257     return false;
 258 }
 259
 260
 261 void
 262 MSHR::deallocate()
 263 {
 264     assert(targets.empty());
 265     targets.resetFlags();
 266     assert(deferredTargets.isReset());
 267     inService = false;
 268 }
 269
 270 /*
 271  * Adds a target to an MSHR
 272  */
 273 void
 274 MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order)
 275 {
 276     // assume we'd never issue a prefetch when we've got an
 277     // outstanding miss
 278     assert(pkt->cmd != MemCmd::HardPFReq);
 279
 280     // uncacheable accesses always allocate a new MSHR, and cacheable
 281     // accesses ignore any uncacheable MSHRs, thus we should never
 282     // have targets addded if originally allocated uncacheable
 283     assert(!_isUncacheable);
 284
 285     // if there's a request already in service for this MSHR, we will
 286     // have to defer the new target until after the response if any of
 287     // the following are true:
 288     // - there are other targets already deferred
 289     // - there's a pending invalidate to be applied after the response
 290     //   comes back (but before this target is processed)
 291     // - this target requires an exclusive block and either we're not
 292     //   getting an exclusive block back or we have already snooped
 293     //   another read request that will downgrade our exclusive block
 294     //   to shared
 295     if (inService &&
 296         (!deferredTargets.empty() || hasPostInvalidate() ||
 297          (pkt->needsExclusive() &&
 298           (!isPendingDirty() || hasPostDowngrade() || isForward)))) {
 299         // need to put on deferred list
 300         if (hasPostInvalidate())
 301             replaceUpgrade(pkt);
 302         deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true);
 303     } else {
 304         // No request outstanding, or still OK to append to
 305         // outstanding request: append to regular target list.  Only
 306         // mark pending if current request hasn't been issued yet
 307         // (isn't in service).
 308         targets.add(pkt, whenReady, _order, Target::FromCPU, !inService);
 309     }
 310 }
 311
 312 bool
 313 MSHR::handleSnoop(PacketPtr pkt, Counter _order)
 314 {
 315     DPRINTF(Cache, "%s for %s addr %#llx size %d\n", __func__,
 316             pkt->cmdString(), pkt->getAddr(), pkt->getSize());
 317     if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
 318         // Request has not been issued yet, or it's been issued
 319         // locally but is buffered unissued at some downstream cache
 320         // which is forwarding us this snoop.  Either way, the packet
 321         // we're snooping logically precedes this MSHR's request, so
 322         // the snoop has no impact on the MSHR, but must be processed
 323         // in the standard way by the cache.  The only exception is
 324         // that if we're an L2+ cache buffering an UpgradeReq from a
 325         // higher-level cache, and the snoop is invalidating, then our
 326         // buffered upgrades must be converted to read exclusives,
 327         // since the upper-level cache no longer has a valid copy.
 328         // That is, even though the upper-level cache got out on its
 329         // local bus first, some other invalidating transaction
 330         // reached the global bus before the upgrade did.
 331         if (pkt->needsExclusive()) {
 332             targets.replaceUpgrades();
 333             deferredTargets.replaceUpgrades();
 334         }
 335
 336         return false;
 337     }
 338
 339     // From here on down, the request issued by this MSHR logically
 340     // precedes the request we're snooping.
 341     if (pkt->needsExclusive()) {
 342         // snooped request still precedes the re-request we'll have to
 343         // issue for deferred targets, if any...
 344         deferredTargets.replaceUpgrades();
 345     }
 346
 347     if (hasPostInvalidate()) {
 348         // a prior snoop has already appended an invalidation, so
 349         // logically we don't have the block anymore; no need for
 350         // further snooping.
 351         return true;
 352     }
 353
 354     if (isPendingDirty() || pkt->isInvalidate()) {
 355         // We need to save and replay the packet in two cases:
 356         // 1. We're awaiting an exclusive copy, so ownership is pending,
 357         //    and we need to respond after we receive data.
 358         // 2. It's an invalidation (e.g., UpgradeReq), and we need
 359         //    to forward the snoop up the hierarchy after the current
 360         //    transaction completes.
 361
 362         // Actual target device (typ. a memory) will delete the
 363         // packet on reception, so we need to save a copy here.
 364
 365         // Clear flags and also allocate new data as the original
 366         // packet data storage may have been deleted by the time we
 367         // get to send this packet.
 368         PacketPtr cp_pkt = nullptr;
 369
 370         if (isPendingDirty()) {
 371             // Case 1: The new packet will need to get the response from the
 372             // MSHR already queued up here
 373             cp_pkt = new Packet(pkt, true, true);
 374             pkt->assertMemInhibit();
 375             // in the case of an uncacheable request there is no need
 376             // to set the exclusive flag, but since the recipient does
 377             // not care there is no harm in doing so
 378             pkt->setSupplyExclusive();
 379         } else {
 380             // Case 2: We only need to buffer the packet for information
 381             // purposes; the original request can proceed without waiting
 382             // => Create a copy of the request, as that may get deallocated as
 383             // well
 384             cp_pkt = new Packet(new Request(*pkt->req), pkt->cmd);
 385             DPRINTF(Cache, "Copying packet %p -> %p and request %p -> %p\n",
 386                     pkt, cp_pkt, pkt->req, cp_pkt->req);
 387         }
 388         targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
 389                     downstreamPending && targets.needsExclusive);
 390
 391         if (pkt->needsExclusive()) {
 392             // This transaction will take away our pending copy
 393             postInvalidate = true;
 394         }
 395     }
 396
 397     if (!pkt->needsExclusive() && !pkt->req->isUncacheable()) {
 398         // This transaction will get a read-shared copy, downgrading
 399         // our copy if we had an exclusive one
 400         postDowngrade = true;
 401         pkt->assertShared();
 402     }
 403
 404     return true;
 405 }
 406
 407
 408 bool
 409 MSHR::promoteDeferredTargets()
 410 {
 411     assert(targets.empty());
 412     if (deferredTargets.empty()) {
 413         return false;
 414     }
 415
 416     // swap targets & deferredTargets lists
 417     std::swap(targets, deferredTargets);
 418
 419     // clear deferredTargets flags
 420     deferredTargets.resetFlags();
 421
 422     order = targets.front().order;
 423     readyTime = std::max(curTick(), targets.front().readyTime);
 424
 425     return true;
 426 }
 427
 428
 429 void
 430 MSHR::handleFill(PacketPtr pkt, CacheBlk *blk)
 431 {
 432     if (!pkt->sharedAsserted()
 433         && !(hasPostInvalidate() || hasPostDowngrade())
 434         && deferredTargets.needsExclusive) {
 435         // We got an exclusive response, but we have deferred targets
 436         // which are waiting to request an exclusive copy (not because
 437         // of a pending invalidate).  This can happen if the original
 438         // request was for a read-only (non-exclusive) block, but we
 439         // got an exclusive copy anyway because of the E part of the
 440         // MOESI/MESI protocol.  Since we got the exclusive copy
 441         // there's no need to defer the targets, so move them up to
 442         // the regular target list.
 443         assert(!targets.needsExclusive);
 444         targets.needsExclusive = true;
 445         // if any of the deferred targets were upper-level cache
 446         // requests marked downstreamPending, need to clear that
 447         assert(!downstreamPending);  // not pending here anymore
 448         deferredTargets.clearDownstreamPending();
 449         // this clears out deferredTargets too
 450         targets.splice(targets.end(), deferredTargets);
 451         deferredTargets.resetFlags();
 452     }
 453 }
 454
 455
 456 bool
 457 MSHR::checkFunctional(PacketPtr pkt)
 458 {
 459     // For printing, we treat the MSHR as a whole as single entity.
 460     // For other requests, we iterate over the individual targets
 461     // since that's where the actual data lies.
 462     if (pkt->isPrint()) {
 463         pkt->checkFunctional(this, blkAddr, isSecure, blkSize, NULL);
 464         return false;
 465     } else {
 466         return (targets.checkFunctional(pkt) ||
 467                 deferredTargets.checkFunctional(pkt));
 468     }
 469 }
 470
 471
 472 void
 473 MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
 474 {
 475     ccprintf(os, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
 476              prefix, blkAddr, blkAddr + blkSize - 1,
 477              isSecure ? "s" : "ns",
 478              isForward ? "Forward" : "",
 479              isForwardNoResponse() ? "ForwNoResp" : "",
 480              needsExclusive() ? "Excl" : "",
 481              _isUncacheable ? "Unc" : "",
 482              inService ? "InSvc" : "",
 483              downstreamPending ? "DwnPend" : "",
 484              hasPostInvalidate() ? "PostInv" : "",
 485              hasPostDowngrade() ? "PostDowngr" : "");
 486
 487     ccprintf(os, "%s  Targets:\n", prefix);
 488     targets.print(os, verbosity, prefix + "    ");
 489     if (!deferredTargets.empty()) {
 490         ccprintf(os, "%s  Deferred Targets:\n", prefix);
 491         deferredTargets.print(os, verbosity, prefix + "      ");
 492     }
 493 }
 494
 495 std::string
 496 MSHR::print() const
 497 {
 498     ostringstream str;
 499     print(str);
 500     return str.str();
 501 }