src/mem/cache/mshr.cc

   1 /*
   2  * Copyright (c) 2012-2013, 2015-2016 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() : downstreamPending(false),
  65                pendingModified(false),
  66                postInvalidate(false), postDowngrade(false),
  67                isForward(false), allocOnFill(false)
  68 {
  69 }
  70
  71 MSHR::TargetList::TargetList()
  72     : needsWritable(false), hasUpgrade(false)
  73 {}
  74
  75
  76 inline void
  77 MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
  78                       Counter order, Target::Source source, bool markPending)
  79 {
  80     if (source != Target::FromSnoop) {
  81         if (pkt->needsWritable()) {
  82             needsWritable = true;
  83         }
  84
  85         // StoreCondReq is effectively an upgrade if it's in an MSHR
  86         // since it would have been failed already if we didn't have a
  87         // read-only copy
  88         if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
  89             hasUpgrade = true;
  90         }
  91     }
  92
  93     if (markPending) {
  94         // Iterate over the SenderState stack and see if we find
  95         // an MSHR entry. If we do, set the downstreamPending
  96         // flag. Otherwise, do nothing.
  97         MSHR *mshr = pkt->findNextSenderState<MSHR>();
  98         if (mshr != nullptr) {
  99             assert(!mshr->downstreamPending);
 100             mshr->downstreamPending = true;
 101         } else {
 102             // No need to clear downstreamPending later
 103             markPending = false;
 104         }
 105     }
 106
 107     emplace_back(pkt, readyTime, order, source, markPending);
 108 }
 109
 110
 111 static void
 112 replaceUpgrade(PacketPtr pkt)
 113 {
 114     // remember if the current packet has data allocated
 115     bool has_data = pkt->hasData() || pkt->hasRespData();
 116
 117     if (pkt->cmd == MemCmd::UpgradeReq) {
 118         pkt->cmd = MemCmd::ReadExReq;
 119         DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
 120     } else if (pkt->cmd == MemCmd::SCUpgradeReq) {
 121         pkt->cmd = MemCmd::SCUpgradeFailReq;
 122         DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
 123     } else if (pkt->cmd == MemCmd::StoreCondReq) {
 124         pkt->cmd = MemCmd::StoreCondFailReq;
 125         DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
 126     }
 127
 128     if (!has_data) {
 129         // there is no sensible way of setting the data field if the
 130         // new command actually would carry data
 131         assert(!pkt->hasData());
 132
 133         if (pkt->hasRespData()) {
 134             // we went from a packet that had no data (neither request,
 135             // nor response), to one that does, and therefore we need to
 136             // actually allocate space for the data payload
 137             pkt->allocate();
 138         }
 139     }
 140 }
 141
 142
 143 void
 144 MSHR::TargetList::replaceUpgrades()
 145 {
 146     if (!hasUpgrade)
 147         return;
 148
 149     for (auto& t : *this) {
 150         replaceUpgrade(t.pkt);
 151     }
 152
 153     hasUpgrade = false;
 154 }
 155
 156
 157 void
 158 MSHR::TargetList::clearDownstreamPending()
 159 {
 160     for (auto& t : *this) {
 161         if (t.markedPending) {
 162             // Iterate over the SenderState stack and see if we find
 163             // an MSHR entry. If we find one, clear the
 164             // downstreamPending flag by calling
 165             // clearDownstreamPending(). This recursively clears the
 166             // downstreamPending flag in all caches this packet has
 167             // passed through.
 168             MSHR *mshr = t.pkt->findNextSenderState<MSHR>();
 169             if (mshr != nullptr) {
 170                 mshr->clearDownstreamPending();
 171             }
 172         }
 173     }
 174 }
 175
 176
 177 bool
 178 MSHR::TargetList::checkFunctional(PacketPtr pkt)
 179 {
 180     for (auto& t : *this) {
 181         if (pkt->checkFunctional(t.pkt)) {
 182             return true;
 183         }
 184     }
 185
 186     return false;
 187 }
 188
 189
 190 void
 191 MSHR::TargetList::print(std::ostream &os, int verbosity,
 192                         const std::string &prefix) const
 193 {
 194     for (auto& t : *this) {
 195         const char *s;
 196         switch (t.source) {
 197           case Target::FromCPU:
 198             s = "FromCPU";
 199             break;
 200           case Target::FromSnoop:
 201             s = "FromSnoop";
 202             break;
 203           case Target::FromPrefetcher:
 204             s = "FromPrefetcher";
 205             break;
 206           default:
 207             s = "";
 208             break;
 209         }
 210         ccprintf(os, "%s%s: ", prefix, s);
 211         t.pkt->print(os, verbosity, "");
 212     }
 213 }
 214
 215
 216 void
 217 MSHR::allocate(Addr blk_addr, unsigned blk_size, PacketPtr target,
 218                Tick when_ready, Counter _order, bool alloc_on_fill)
 219 {
 220     blkAddr = blk_addr;
 221     blkSize = blk_size;
 222     isSecure = target->isSecure();
 223     readyTime = when_ready;
 224     order = _order;
 225     assert(target);
 226     isForward = false;
 227     allocOnFill = alloc_on_fill;
 228     _isUncacheable = target->req->isUncacheable();
 229     inService = false;
 230     downstreamPending = false;
 231     assert(targets.isReset());
 232     // Don't know of a case where we would allocate a new MSHR for a
 233     // snoop (mem-side request), so set source according to request here
 234     Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
 235         Target::FromPrefetcher : Target::FromCPU;
 236     targets.add(target, when_ready, _order, source, true);
 237     assert(deferredTargets.isReset());
 238 }
 239
 240
 241 void
 242 MSHR::clearDownstreamPending()
 243 {
 244     assert(downstreamPending);
 245     downstreamPending = false;
 246     // recursively clear flag on any MSHRs we will be forwarding
 247     // responses to
 248     targets.clearDownstreamPending();
 249 }
 250
 251 void
 252 MSHR::markInService(bool pending_modified_resp)
 253 {
 254     assert(!inService);
 255
 256     inService = true;
 257     pendingModified = targets.needsWritable || pending_modified_resp;
 258     postInvalidate = postDowngrade = false;
 259
 260     if (!downstreamPending) {
 261         // let upstream caches know that the request has made it to a
 262         // level where it's going to get a response
 263         targets.clearDownstreamPending();
 264     }
 265 }
 266
 267
 268 void
 269 MSHR::deallocate()
 270 {
 271     assert(targets.empty());
 272     targets.resetFlags();
 273     assert(deferredTargets.isReset());
 274     inService = false;
 275 }
 276
 277 /*
 278  * Adds a target to an MSHR
 279  */
 280 void
 281 MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order,
 282                      bool alloc_on_fill)
 283 {
 284     // assume we'd never issue a prefetch when we've got an
 285     // outstanding miss
 286     assert(pkt->cmd != MemCmd::HardPFReq);
 287
 288     // uncacheable accesses always allocate a new MSHR, and cacheable
 289     // accesses ignore any uncacheable MSHRs, thus we should never
 290     // have targets addded if originally allocated uncacheable
 291     assert(!_isUncacheable);
 292
 293     // potentially re-evaluate whether we should allocate on a fill or
 294     // not
 295     allocOnFill = allocOnFill || alloc_on_fill;
 296
 297     // if there's a request already in service for this MSHR, we will
 298     // have to defer the new target until after the response if any of
 299     // the following are true:
 300     // - there are other targets already deferred
 301     // - there's a pending invalidate to be applied after the response
 302     //   comes back (but before this target is processed)
 303     // - this target requires a writable block and either we're not
 304     //   getting a writable block back or we have already snooped
 305     //   another read request that will downgrade our writable block
 306     //   to non-writable (Shared or Owned)
 307     if (inService &&
 308         (!deferredTargets.empty() || hasPostInvalidate() ||
 309          (pkt->needsWritable() &&
 310           (!isPendingModified() || hasPostDowngrade() || isForward)))) {
 311         // need to put on deferred list
 312         if (hasPostInvalidate())
 313             replaceUpgrade(pkt);
 314         deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true);
 315     } else {
 316         // No request outstanding, or still OK to append to
 317         // outstanding request: append to regular target list.  Only
 318         // mark pending if current request hasn't been issued yet
 319         // (isn't in service).
 320         targets.add(pkt, whenReady, _order, Target::FromCPU, !inService);
 321     }
 322 }
 323
 324 bool
 325 MSHR::handleSnoop(PacketPtr pkt, Counter _order)
 326 {
 327     DPRINTF(Cache, "%s for %s addr %#llx size %d\n", __func__,
 328             pkt->cmdString(), pkt->getAddr(), pkt->getSize());
 329
 330     // when we snoop packets the needsWritable and isInvalidate flags
 331     // should always be the same, however, this assumes that we never
 332     // snoop writes as they are currently not marked as invalidations
 333     panic_if(pkt->needsWritable() != pkt->isInvalidate(),
 334              "%s got snoop %s to addr %#llx where needsWritable, "
 335              "does not match isInvalidate", name(), pkt->cmdString(),
 336              pkt->getAddr());
 337
 338     if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
 339         // Request has not been issued yet, or it's been issued
 340         // locally but is buffered unissued at some downstream cache
 341         // which is forwarding us this snoop.  Either way, the packet
 342         // we're snooping logically precedes this MSHR's request, so
 343         // the snoop has no impact on the MSHR, but must be processed
 344         // in the standard way by the cache.  The only exception is
 345         // that if we're an L2+ cache buffering an UpgradeReq from a
 346         // higher-level cache, and the snoop is invalidating, then our
 347         // buffered upgrades must be converted to read exclusives,
 348         // since the upper-level cache no longer has a valid copy.
 349         // That is, even though the upper-level cache got out on its
 350         // local bus first, some other invalidating transaction
 351         // reached the global bus before the upgrade did.
 352         if (pkt->needsWritable()) {
 353             targets.replaceUpgrades();
 354             deferredTargets.replaceUpgrades();
 355         }
 356
 357         return false;
 358     }
 359
 360     // From here on down, the request issued by this MSHR logically
 361     // precedes the request we're snooping.
 362     if (pkt->needsWritable()) {
 363         // snooped request still precedes the re-request we'll have to
 364         // issue for deferred targets, if any...
 365         deferredTargets.replaceUpgrades();
 366     }
 367
 368     if (hasPostInvalidate()) {
 369         // a prior snoop has already appended an invalidation, so
 370         // logically we don't have the block anymore; no need for
 371         // further snooping.
 372         return true;
 373     }
 374
 375     if (isPendingModified() || pkt->isInvalidate()) {
 376         // We need to save and replay the packet in two cases:
 377         // 1. We're awaiting a writable copy (Modified or Exclusive),
 378         //    so this MSHR is the orgering point, and we need to respond
 379         //    after we receive data.
 380         // 2. It's an invalidation (e.g., UpgradeReq), and we need
 381         //    to forward the snoop up the hierarchy after the current
 382         //    transaction completes.
 383
 384         // Start by determining if we will eventually respond or not,
 385         // matching the conditions checked in Cache::handleSnoop
 386         bool will_respond = isPendingModified() && pkt->needsResponse() &&
 387             pkt->cmd != MemCmd::InvalidateReq;
 388
 389         // The packet we are snooping may be deleted by the time we
 390         // actually process the target, and we consequently need to
 391         // save a copy here. Clear flags and also allocate new data as
 392         // the original packet data storage may have been deleted by
 393         // the time we get to process this packet. In the cases where
 394         // we are not responding after handling the snoop we also need
 395         // to create a copy of the request to be on the safe side. In
 396         // the latter case the cache is responsible for deleting both
 397         // the packet and the request as part of handling the deferred
 398         // snoop.
 399         PacketPtr cp_pkt = will_respond ? new Packet(pkt, true, true) :
 400             new Packet(new Request(*pkt->req), pkt->cmd);
 401
 402         if (isPendingModified()) {
 403             // we are the ordering point, and will consequently
 404             // respond, and depending on whether the packet
 405             // needsWritable or not we either pass a Shared line or a
 406             // Modified line
 407             pkt->setCacheResponding();
 408
 409             // inform the cache hierarchy that this cache had the line
 410             // in the Modified state, even if the response is passed
 411             // as Shared (and thus non-writable)
 412             pkt->setResponderHadWritable();
 413
 414             // in the case of an uncacheable request there is no need
 415             // to set the responderHadWritable flag, but since the
 416             // recipient does not care there is no harm in doing so
 417         }
 418         targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
 419                     downstreamPending && targets.needsWritable);
 420
 421         if (pkt->needsWritable()) {
 422             // This transaction will take away our pending copy
 423             postInvalidate = true;
 424         }
 425     }
 426
 427     if (!pkt->needsWritable() && !pkt->req->isUncacheable()) {
 428         // This transaction will get a read-shared copy, downgrading
 429         // our copy if we had a writable one
 430         postDowngrade = true;
 431         // make sure that any downstream cache does not respond with a
 432         // writable (and dirty) copy even if it has one, unless it was
 433         // explicitly asked for one
 434         pkt->setHasSharers();
 435     }
 436
 437     return true;
 438 }
 439
 440
 441 bool
 442 MSHR::promoteDeferredTargets()
 443 {
 444     assert(targets.empty());
 445     if (deferredTargets.empty()) {
 446         return false;
 447     }
 448
 449     // swap targets & deferredTargets lists
 450     std::swap(targets, deferredTargets);
 451
 452     // clear deferredTargets flags
 453     deferredTargets.resetFlags();
 454
 455     order = targets.front().order;
 456     readyTime = std::max(curTick(), targets.front().readyTime);
 457
 458     return true;
 459 }
 460
 461
 462 void
 463 MSHR::promoteWritable()
 464 {
 465     if (deferredTargets.needsWritable &&
 466         !(hasPostInvalidate() || hasPostDowngrade())) {
 467         // We got a writable response, but we have deferred targets
 468         // which are waiting to request a writable copy (not because
 469         // of a pending invalidate).  This can happen if the original
 470         // request was for a read-only block, but we got a writable
 471         // response anyway. Since we got the writable copy there's no
 472         // need to defer the targets, so move them up to the regular
 473         // target list.
 474         assert(!targets.needsWritable);
 475         targets.needsWritable = true;
 476         // if any of the deferred targets were upper-level cache
 477         // requests marked downstreamPending, need to clear that
 478         assert(!downstreamPending);  // not pending here anymore
 479         deferredTargets.clearDownstreamPending();
 480         // this clears out deferredTargets too
 481         targets.splice(targets.end(), deferredTargets);
 482         deferredTargets.resetFlags();
 483     }
 484 }
 485
 486
 487 bool
 488 MSHR::checkFunctional(PacketPtr pkt)
 489 {
 490     // For printing, we treat the MSHR as a whole as single entity.
 491     // For other requests, we iterate over the individual targets
 492     // since that's where the actual data lies.
 493     if (pkt->isPrint()) {
 494         pkt->checkFunctional(this, blkAddr, isSecure, blkSize, nullptr);
 495         return false;
 496     } else {
 497         return (targets.checkFunctional(pkt) ||
 498                 deferredTargets.checkFunctional(pkt));
 499     }
 500 }
 501
 502 bool
 503 MSHR::sendPacket(Cache &cache)
 504 {
 505     return cache.sendMSHRQueuePacket(this);
 506 }
 507
 508 void
 509 MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
 510 {
 511     ccprintf(os, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
 512              prefix, blkAddr, blkAddr + blkSize - 1,
 513              isSecure ? "s" : "ns",
 514              isForward ? "Forward" : "",
 515              allocOnFill ? "AllocOnFill" : "",
 516              needsWritable() ? "Wrtbl" : "",
 517              _isUncacheable ? "Unc" : "",
 518              inService ? "InSvc" : "",
 519              downstreamPending ? "DwnPend" : "",
 520              hasPostInvalidate() ? "PostInv" : "",
 521              hasPostDowngrade() ? "PostDowngr" : "");
 522
 523     ccprintf(os, "%s  Targets:\n", prefix);
 524     targets.print(os, verbosity, prefix + "    ");
 525     if (!deferredTargets.empty()) {
 526         ccprintf(os, "%s  Deferred Targets:\n", prefix);
 527         deferredTargets.print(os, verbosity, prefix + "      ");
 528     }
 529 }
 530
 531 std::string
 532 MSHR::print() const
 533 {
 534     ostringstream str;
 535     print(str);
 536     return str.str();
 537 }