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 "mem/cache/mshr.hh"
  51
  52 #include <algorithm>
  53 #include <cassert>
  54 #include <string>
  55 #include <vector>
  56
  57 #include "base/misc.hh"
  58 #include "base/types.hh"
  59 #include "debug/Cache.hh"
  60 #include "mem/cache/cache.hh"
  61 #include "sim/core.hh"
  62
  63 using namespace std;
  64
  65 MSHR::MSHR() : downstreamPending(false),
  66                pendingModified(false),
  67                postInvalidate(false), postDowngrade(false),
  68                isForward(false), allocOnFill(false)
  69 {
  70 }
  71
  72 MSHR::TargetList::TargetList()
  73     : needsWritable(false), hasUpgrade(false)
  74 {}
  75
  76
  77 inline void
  78 MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
  79                       Counter order, Target::Source source, bool markPending)
  80 {
  81     if (source != Target::FromSnoop) {
  82         if (pkt->needsWritable()) {
  83             needsWritable = true;
  84         }
  85
  86         // StoreCondReq is effectively an upgrade if it's in an MSHR
  87         // since it would have been failed already if we didn't have a
  88         // read-only copy
  89         if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
  90             hasUpgrade = true;
  91         }
  92     }
  93
  94     if (markPending) {
  95         // Iterate over the SenderState stack and see if we find
  96         // an MSHR entry. If we do, set the downstreamPending
  97         // flag. Otherwise, do nothing.
  98         MSHR *mshr = pkt->findNextSenderState<MSHR>();
  99         if (mshr != nullptr) {
 100             assert(!mshr->downstreamPending);
 101             mshr->downstreamPending = true;
 102         } else {
 103             // No need to clear downstreamPending later
 104             markPending = false;
 105         }
 106     }
 107
 108     emplace_back(pkt, readyTime, order, source, markPending);
 109 }
 110
 111
 112 static void
 113 replaceUpgrade(PacketPtr pkt)
 114 {
 115     // remember if the current packet has data allocated
 116     bool has_data = pkt->hasData() || pkt->hasRespData();
 117
 118     if (pkt->cmd == MemCmd::UpgradeReq) {
 119         pkt->cmd = MemCmd::ReadExReq;
 120         DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
 121     } else if (pkt->cmd == MemCmd::SCUpgradeReq) {
 122         pkt->cmd = MemCmd::SCUpgradeFailReq;
 123         DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
 124     } else if (pkt->cmd == MemCmd::StoreCondReq) {
 125         pkt->cmd = MemCmd::StoreCondFailReq;
 126         DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
 127     }
 128
 129     if (!has_data) {
 130         // there is no sensible way of setting the data field if the
 131         // new command actually would carry data
 132         assert(!pkt->hasData());
 133
 134         if (pkt->hasRespData()) {
 135             // we went from a packet that had no data (neither request,
 136             // nor response), to one that does, and therefore we need to
 137             // actually allocate space for the data payload
 138             pkt->allocate();
 139         }
 140     }
 141 }
 142
 143
 144 void
 145 MSHR::TargetList::replaceUpgrades()
 146 {
 147     if (!hasUpgrade)
 148         return;
 149
 150     for (auto& t : *this) {
 151         replaceUpgrade(t.pkt);
 152     }
 153
 154     hasUpgrade = false;
 155 }
 156
 157
 158 void
 159 MSHR::TargetList::clearDownstreamPending()
 160 {
 161     for (auto& t : *this) {
 162         if (t.markedPending) {
 163             // Iterate over the SenderState stack and see if we find
 164             // an MSHR entry. If we find one, clear the
 165             // downstreamPending flag by calling
 166             // clearDownstreamPending(). This recursively clears the
 167             // downstreamPending flag in all caches this packet has
 168             // passed through.
 169             MSHR *mshr = t.pkt->findNextSenderState<MSHR>();
 170             if (mshr != nullptr) {
 171                 mshr->clearDownstreamPending();
 172             }
 173         }
 174     }
 175 }
 176
 177
 178 bool
 179 MSHR::TargetList::checkFunctional(PacketPtr pkt)
 180 {
 181     for (auto& t : *this) {
 182         if (pkt->checkFunctional(t.pkt)) {
 183             return true;
 184         }
 185     }
 186
 187     return false;
 188 }
 189
 190
 191 void
 192 MSHR::TargetList::print(std::ostream &os, int verbosity,
 193                         const std::string &prefix) const
 194 {
 195     for (auto& t : *this) {
 196         const char *s;
 197         switch (t.source) {
 198           case Target::FromCPU:
 199             s = "FromCPU";
 200             break;
 201           case Target::FromSnoop:
 202             s = "FromSnoop";
 203             break;
 204           case Target::FromPrefetcher:
 205             s = "FromPrefetcher";
 206             break;
 207           default:
 208             s = "";
 209             break;
 210         }
 211         ccprintf(os, "%s%s: ", prefix, s);
 212         t.pkt->print(os, verbosity, "");
 213     }
 214 }
 215
 216
 217 void
 218 MSHR::allocate(Addr blk_addr, unsigned blk_size, PacketPtr target,
 219                Tick when_ready, Counter _order, bool alloc_on_fill)
 220 {
 221     blkAddr = blk_addr;
 222     blkSize = blk_size;
 223     isSecure = target->isSecure();
 224     readyTime = when_ready;
 225     order = _order;
 226     assert(target);
 227     isForward = false;
 228     allocOnFill = alloc_on_fill;
 229     _isUncacheable = target->req->isUncacheable();
 230     inService = false;
 231     downstreamPending = false;
 232     assert(targets.isReset());
 233     // Don't know of a case where we would allocate a new MSHR for a
 234     // snoop (mem-side request), so set source according to request here
 235     Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
 236         Target::FromPrefetcher : Target::FromCPU;
 237     targets.add(target, when_ready, _order, source, true);
 238     assert(deferredTargets.isReset());
 239 }
 240
 241
 242 void
 243 MSHR::clearDownstreamPending()
 244 {
 245     assert(downstreamPending);
 246     downstreamPending = false;
 247     // recursively clear flag on any MSHRs we will be forwarding
 248     // responses to
 249     targets.clearDownstreamPending();
 250 }
 251
 252 void
 253 MSHR::markInService(bool pending_modified_resp)
 254 {
 255     assert(!inService);
 256
 257     inService = true;
 258     pendingModified = targets.needsWritable || pending_modified_resp;
 259     postInvalidate = postDowngrade = false;
 260
 261     if (!downstreamPending) {
 262         // let upstream caches know that the request has made it to a
 263         // level where it's going to get a response
 264         targets.clearDownstreamPending();
 265     }
 266 }
 267
 268
 269 void
 270 MSHR::deallocate()
 271 {
 272     assert(targets.empty());
 273     targets.resetFlags();
 274     assert(deferredTargets.isReset());
 275     inService = false;
 276 }
 277
 278 /*
 279  * Adds a target to an MSHR
 280  */
 281 void
 282 MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order,
 283                      bool alloc_on_fill)
 284 {
 285     // assume we'd never issue a prefetch when we've got an
 286     // outstanding miss
 287     assert(pkt->cmd != MemCmd::HardPFReq);
 288
 289     // uncacheable accesses always allocate a new MSHR, and cacheable
 290     // accesses ignore any uncacheable MSHRs, thus we should never
 291     // have targets addded if originally allocated uncacheable
 292     assert(!_isUncacheable);
 293
 294     // potentially re-evaluate whether we should allocate on a fill or
 295     // not
 296     allocOnFill = allocOnFill || alloc_on_fill;
 297
 298     // if there's a request already in service for this MSHR, we will
 299     // have to defer the new target until after the response if any of
 300     // the following are true:
 301     // - there are other targets already deferred
 302     // - there's a pending invalidate to be applied after the response
 303     //   comes back (but before this target is processed)
 304     // - this target requires a writable block and either we're not
 305     //   getting a writable block back or we have already snooped
 306     //   another read request that will downgrade our writable block
 307     //   to non-writable (Shared or Owned)
 308     if (inService &&
 309         (!deferredTargets.empty() || hasPostInvalidate() ||
 310          (pkt->needsWritable() &&
 311           (!isPendingModified() || hasPostDowngrade() || isForward)))) {
 312         // need to put on deferred list
 313         if (hasPostInvalidate())
 314             replaceUpgrade(pkt);
 315         deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true);
 316     } else {
 317         // No request outstanding, or still OK to append to
 318         // outstanding request: append to regular target list.  Only
 319         // mark pending if current request hasn't been issued yet
 320         // (isn't in service).
 321         targets.add(pkt, whenReady, _order, Target::FromCPU, !inService);
 322     }
 323 }
 324
 325 bool
 326 MSHR::handleSnoop(PacketPtr pkt, Counter _order)
 327 {
 328     DPRINTF(Cache, "%s for %s addr %#llx size %d\n", __func__,
 329             pkt->cmdString(), pkt->getAddr(), pkt->getSize());
 330
 331     // when we snoop packets the needsWritable and isInvalidate flags
 332     // should always be the same, however, this assumes that we never
 333     // snoop writes as they are currently not marked as invalidations
 334     panic_if(pkt->needsWritable() != pkt->isInvalidate(),
 335              "%s got snoop %s to addr %#llx where needsWritable, "
 336              "does not match isInvalidate", name(), pkt->cmdString(),
 337              pkt->getAddr());
 338
 339     if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
 340         // Request has not been issued yet, or it's been issued
 341         // locally but is buffered unissued at some downstream cache
 342         // which is forwarding us this snoop.  Either way, the packet
 343         // we're snooping logically precedes this MSHR's request, so
 344         // the snoop has no impact on the MSHR, but must be processed
 345         // in the standard way by the cache.  The only exception is
 346         // that if we're an L2+ cache buffering an UpgradeReq from a
 347         // higher-level cache, and the snoop is invalidating, then our
 348         // buffered upgrades must be converted to read exclusives,
 349         // since the upper-level cache no longer has a valid copy.
 350         // That is, even though the upper-level cache got out on its
 351         // local bus first, some other invalidating transaction
 352         // reached the global bus before the upgrade did.
 353         if (pkt->needsWritable()) {
 354             targets.replaceUpgrades();
 355             deferredTargets.replaceUpgrades();
 356         }
 357
 358         return false;
 359     }
 360
 361     // From here on down, the request issued by this MSHR logically
 362     // precedes the request we're snooping.
 363     if (pkt->needsWritable()) {
 364         // snooped request still precedes the re-request we'll have to
 365         // issue for deferred targets, if any...
 366         deferredTargets.replaceUpgrades();
 367     }
 368
 369     if (hasPostInvalidate()) {
 370         // a prior snoop has already appended an invalidation, so
 371         // logically we don't have the block anymore; no need for
 372         // further snooping.
 373         return true;
 374     }
 375
 376     if (isPendingModified() || pkt->isInvalidate()) {
 377         // We need to save and replay the packet in two cases:
 378         // 1. We're awaiting a writable copy (Modified or Exclusive),
 379         //    so this MSHR is the orgering point, and we need to respond
 380         //    after we receive data.
 381         // 2. It's an invalidation (e.g., UpgradeReq), and we need
 382         //    to forward the snoop up the hierarchy after the current
 383         //    transaction completes.
 384
 385         // Start by determining if we will eventually respond or not,
 386         // matching the conditions checked in Cache::handleSnoop
 387         bool will_respond = isPendingModified() && pkt->needsResponse() &&
 388             pkt->cmd != MemCmd::InvalidateReq;
 389
 390         // The packet we are snooping may be deleted by the time we
 391         // actually process the target, and we consequently need to
 392         // save a copy here. Clear flags and also allocate new data as
 393         // the original packet data storage may have been deleted by
 394         // the time we get to process this packet. In the cases where
 395         // we are not responding after handling the snoop we also need
 396         // to create a copy of the request to be on the safe side. In
 397         // the latter case the cache is responsible for deleting both
 398         // the packet and the request as part of handling the deferred
 399         // snoop.
 400         PacketPtr cp_pkt = will_respond ? new Packet(pkt, true, true) :
 401             new Packet(new Request(*pkt->req), pkt->cmd);
 402
 403         if (isPendingModified()) {
 404             // we are the ordering point, and will consequently
 405             // respond, and depending on whether the packet
 406             // needsWritable or not we either pass a Shared line or a
 407             // Modified line
 408             pkt->setCacheResponding();
 409
 410             // inform the cache hierarchy that this cache had the line
 411             // in the Modified state, even if the response is passed
 412             // as Shared (and thus non-writable)
 413             pkt->setResponderHadWritable();
 414
 415             // in the case of an uncacheable request there is no need
 416             // to set the responderHadWritable flag, but since the
 417             // recipient does not care there is no harm in doing so
 418         }
 419         targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
 420                     downstreamPending && targets.needsWritable);
 421
 422         if (pkt->needsWritable()) {
 423             // This transaction will take away our pending copy
 424             postInvalidate = true;
 425         }
 426     }
 427
 428     if (!pkt->needsWritable() && !pkt->req->isUncacheable()) {
 429         // This transaction will get a read-shared copy, downgrading
 430         // our copy if we had a writable one
 431         postDowngrade = true;
 432         // make sure that any downstream cache does not respond with a
 433         // writable (and dirty) copy even if it has one, unless it was
 434         // explicitly asked for one
 435         pkt->setHasSharers();
 436     }
 437
 438     return true;
 439 }
 440
 441
 442 bool
 443 MSHR::promoteDeferredTargets()
 444 {
 445     assert(targets.empty());
 446     if (deferredTargets.empty()) {
 447         return false;
 448     }
 449
 450     // swap targets & deferredTargets lists
 451     std::swap(targets, deferredTargets);
 452
 453     // clear deferredTargets flags
 454     deferredTargets.resetFlags();
 455
 456     order = targets.front().order;
 457     readyTime = std::max(curTick(), targets.front().readyTime);
 458
 459     return true;
 460 }
 461
 462
 463 void
 464 MSHR::promoteWritable()
 465 {
 466     if (deferredTargets.needsWritable &&
 467         !(hasPostInvalidate() || hasPostDowngrade())) {
 468         // We got a writable response, but we have deferred targets
 469         // which are waiting to request a writable copy (not because
 470         // of a pending invalidate).  This can happen if the original
 471         // request was for a read-only block, but we got a writable
 472         // response anyway. Since we got the writable copy there's no
 473         // need to defer the targets, so move them up to the regular
 474         // target list.
 475         assert(!targets.needsWritable);
 476         targets.needsWritable = true;
 477         // if any of the deferred targets were upper-level cache
 478         // requests marked downstreamPending, need to clear that
 479         assert(!downstreamPending);  // not pending here anymore
 480         deferredTargets.clearDownstreamPending();
 481         // this clears out deferredTargets too
 482         targets.splice(targets.end(), deferredTargets);
 483         deferredTargets.resetFlags();
 484     }
 485 }
 486
 487
 488 bool
 489 MSHR::checkFunctional(PacketPtr pkt)
 490 {
 491     // For printing, we treat the MSHR as a whole as single entity.
 492     // For other requests, we iterate over the individual targets
 493     // since that's where the actual data lies.
 494     if (pkt->isPrint()) {
 495         pkt->checkFunctional(this, blkAddr, isSecure, blkSize, nullptr);
 496         return false;
 497     } else {
 498         return (targets.checkFunctional(pkt) ||
 499                 deferredTargets.checkFunctional(pkt));
 500     }
 501 }
 502
 503 bool
 504 MSHR::sendPacket(Cache &cache)
 505 {
 506     return cache.sendMSHRQueuePacket(this);
 507 }
 508
 509 void
 510 MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
 511 {
 512     ccprintf(os, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
 513              prefix, blkAddr, blkAddr + blkSize - 1,
 514              isSecure ? "s" : "ns",
 515              isForward ? "Forward" : "",
 516              allocOnFill ? "AllocOnFill" : "",
 517              needsWritable() ? "Wrtbl" : "",
 518              _isUncacheable ? "Unc" : "",
 519              inService ? "InSvc" : "",
 520              downstreamPending ? "DwnPend" : "",
 521              hasPostInvalidate() ? "PostInv" : "",
 522              hasPostDowngrade() ? "PostDowngr" : "");
 523
 524     ccprintf(os, "%s  Targets:\n", prefix);
 525     targets.print(os, verbosity, prefix + "    ");
 526     if (!deferredTargets.empty()) {
 527         ccprintf(os, "%s  Deferred Targets:\n", prefix);
 528         deferredTargets.print(os, verbosity, prefix + "      ");
 529     }
 530 }
 531
 532 std::string
 533 MSHR::print() const
 534 {
 535     ostringstream str;
 536     print(str);
 537     return str.str();
 538 }