src/mem/cache/mshr.cc

   1 /*
   2  * Copyright (c) 2012 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()
  65 {
  66     inService = false;
  67     ntargets = 0;
  68     threadNum = InvalidThreadID;
  69     targets = new TargetList();
  70     deferredTargets = new TargetList();
  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     push_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     Iterator end_i = end();
 134     for (Iterator i = begin(); i != end_i; ++i) {
 135         replaceUpgrade(i->pkt);
 136     }
 137
 138     hasUpgrade = false;
 139 }
 140
 141
 142 void
 143 MSHR::TargetList::clearDownstreamPending()
 144 {
 145     Iterator end_i = end();
 146     for (Iterator i = begin(); i != end_i; ++i) {
 147         if (i->markedPending) {
 148             // Iterate over the SenderState stack and see if we find
 149             // an MSHR entry. If we find one, clear the
 150             // downstreamPending flag by calling
 151             // clearDownstreamPending(). This recursively clears the
 152             // downstreamPending flag in all caches this packet has
 153             // passed through.
 154             MSHR *mshr = i->pkt->findNextSenderState<MSHR>();
 155             if (mshr != NULL) {
 156                 mshr->clearDownstreamPending();
 157             }
 158         }
 159     }
 160 }
 161
 162
 163 bool
 164 MSHR::TargetList::checkFunctional(PacketPtr pkt)
 165 {
 166     Iterator end_i = end();
 167     for (Iterator i = begin(); i != end_i; ++i) {
 168         if (pkt->checkFunctional(i->pkt)) {
 169             return true;
 170         }
 171     }
 172
 173     return false;
 174 }
 175
 176
 177 void
 178 MSHR::TargetList::
 179 print(std::ostream &os, int verbosity, const std::string &prefix) const
 180 {
 181     ConstIterator end_i = end();
 182     for (ConstIterator i = begin(); i != end_i; ++i) {
 183         const char *s;
 184         switch (i->source) {
 185           case Target::FromCPU:
 186             s = "FromCPU";
 187             break;
 188           case Target::FromSnoop:
 189             s = "FromSnoop";
 190             break;
 191           case Target::FromPrefetcher:
 192             s = "FromPrefetcher";
 193             break;
 194           default:
 195             s = "";
 196             break;
 197         }
 198         ccprintf(os, "%s%s: ", prefix, s);
 199         i->pkt->print(os, verbosity, "");
 200     }
 201 }
 202
 203
 204 void
 205 MSHR::allocate(Addr _addr, int _size, PacketPtr target,
 206                Tick whenReady, Counter _order)
 207 {
 208     addr = _addr;
 209     size = _size;
 210     readyTime = whenReady;
 211     order = _order;
 212     assert(target);
 213     isForward = false;
 214     _isUncacheable = target->req->isUncacheable();
 215     inService = false;
 216     downstreamPending = false;
 217     threadNum = 0;
 218     ntargets = 1;
 219     assert(targets->isReset());
 220     // Don't know of a case where we would allocate a new MSHR for a
 221     // snoop (mem-side request), so set source according to request here
 222     Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
 223         Target::FromPrefetcher : Target::FromCPU;
 224     targets->add(target, whenReady, _order, source, true);
 225     assert(deferredTargets->isReset());
 226     data = NULL;
 227 }
 228
 229
 230 void
 231 MSHR::clearDownstreamPending()
 232 {
 233     assert(downstreamPending);
 234     downstreamPending = false;
 235     // recursively clear flag on any MSHRs we will be forwarding
 236     // responses to
 237     targets->clearDownstreamPending();
 238 }
 239
 240 bool
 241 MSHR::markInService(PacketPtr pkt)
 242 {
 243     assert(!inService);
 244     if (isForwardNoResponse()) {
 245         // we just forwarded the request packet & don't expect a
 246         // response, so get rid of it
 247         assert(getNumTargets() == 1);
 248         popTarget();
 249         return true;
 250     }
 251     inService = true;
 252     pendingDirty = (targets->needsExclusive ||
 253                     (!pkt->sharedAsserted() && pkt->memInhibitAsserted()));
 254     postInvalidate = postDowngrade = false;
 255
 256     if (!downstreamPending) {
 257         // let upstream caches know that the request has made it to a
 258         // level where it's going to get a response
 259         targets->clearDownstreamPending();
 260     }
 261     return false;
 262 }
 263
 264
 265 void
 266 MSHR::deallocate()
 267 {
 268     assert(targets->empty());
 269     targets->resetFlags();
 270     assert(deferredTargets->isReset());
 271     assert(ntargets == 0);
 272     inService = false;
 273 }
 274
 275 /*
 276  * Adds a target to an MSHR
 277  */
 278 void
 279 MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order)
 280 {
 281     // if there's a request already in service for this MSHR, we will
 282     // have to defer the new target until after the response if any of
 283     // the following are true:
 284     // - there are other targets already deferred
 285     // - there's a pending invalidate to be applied after the response
 286     //   comes back (but before this target is processed)
 287     // - this target requires an exclusive block and either we're not
 288     //   getting an exclusive block back or we have already snooped
 289     //   another read request that will downgrade our exclusive block
 290     //   to shared
 291
 292     // assume we'd never issue a prefetch when we've got an
 293     // outstanding miss
 294     assert(pkt->cmd != MemCmd::HardPFReq);
 295
 296     if (inService &&
 297         (!deferredTargets->empty() || hasPostInvalidate() ||
 298          (pkt->needsExclusive() &&
 299           (!isPendingDirty() || hasPostDowngrade() || isForward)))) {
 300         // need to put on deferred list
 301         if (hasPostInvalidate())
 302             replaceUpgrade(pkt);
 303         deferredTargets->add(pkt, whenReady, _order, Target::FromCPU, true);
 304     } else {
 305         // No request outstanding, or still OK to append to
 306         // outstanding request: append to regular target list.  Only
 307         // mark pending if current request hasn't been issued yet
 308         // (isn't in service).
 309         targets->add(pkt, whenReady, _order, Target::FromCPU, !inService);
 310     }
 311
 312     ++ntargets;
 313 }
 314
 315 bool
 316 MSHR::handleSnoop(PacketPtr pkt, Counter _order)
 317 {
 318     DPRINTF(Cache, "%s for %s address %x size %d\n", __func__,
 319             pkt->cmdString(), pkt->getAddr(), pkt->getSize());
 320     if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
 321         // Request has not been issued yet, or it's been issued
 322         // locally but is buffered unissued at some downstream cache
 323         // which is forwarding us this snoop.  Either way, the packet
 324         // we're snooping logically precedes this MSHR's request, so
 325         // the snoop has no impact on the MSHR, but must be processed
 326         // in the standard way by the cache.  The only exception is
 327         // that if we're an L2+ cache buffering an UpgradeReq from a
 328         // higher-level cache, and the snoop is invalidating, then our
 329         // buffered upgrades must be converted to read exclusives,
 330         // since the upper-level cache no longer has a valid copy.
 331         // That is, even though the upper-level cache got out on its
 332         // local bus first, some other invalidating transaction
 333         // reached the global bus before the upgrade did.
 334         if (pkt->needsExclusive()) {
 335             targets->replaceUpgrades();
 336             deferredTargets->replaceUpgrades();
 337         }
 338
 339         return false;
 340     }
 341
 342     // From here on down, the request issued by this MSHR logically
 343     // precedes the request we're snooping.
 344     if (pkt->needsExclusive()) {
 345         // snooped request still precedes the re-request we'll have to
 346         // issue for deferred targets, if any...
 347         deferredTargets->replaceUpgrades();
 348     }
 349
 350     if (hasPostInvalidate()) {
 351         // a prior snoop has already appended an invalidation, so
 352         // logically we don't have the block anymore; no need for
 353         // further snooping.
 354         return true;
 355     }
 356
 357     if (isPendingDirty() || pkt->isInvalidate()) {
 358         // We need to save and replay the packet in two cases:
 359         // 1. We're awaiting an exclusive copy, so ownership is pending,
 360         //    and we need to respond after we receive data.
 361         // 2. It's an invalidation (e.g., UpgradeReq), and we need
 362         //    to forward the snoop up the hierarchy after the current
 363         //    transaction completes.
 364
 365         // Actual target device (typ. a memory) will delete the
 366         // packet on reception, so we need to save a copy here.
 367         PacketPtr cp_pkt = new Packet(pkt, true);
 368         targets->add(cp_pkt, curTick(), _order, Target::FromSnoop,
 369                      downstreamPending && targets->needsExclusive);
 370         ++ntargets;
 371
 372         if (isPendingDirty()) {
 373             pkt->assertMemInhibit();
 374             pkt->setSupplyExclusive();
 375         }
 376
 377         if (pkt->needsExclusive()) {
 378             // This transaction will take away our pending copy
 379             postInvalidate = true;
 380         }
 381     }
 382
 383     if (!pkt->needsExclusive()) {
 384         // This transaction will get a read-shared copy, downgrading
 385         // our copy if we had an exclusive one
 386         postDowngrade = true;
 387         pkt->assertShared();
 388     }
 389
 390     return true;
 391 }
 392
 393
 394 bool
 395 MSHR::promoteDeferredTargets()
 396 {
 397     assert(targets->empty());
 398     if (deferredTargets->empty()) {
 399         return false;
 400     }
 401
 402     // swap targets & deferredTargets lists
 403     TargetList *tmp = targets;
 404     targets = deferredTargets;
 405     deferredTargets = tmp;
 406
 407     assert(targets->size() == ntargets);
 408
 409     // clear deferredTargets flags
 410     deferredTargets->resetFlags();
 411
 412     order = targets->front().order;
 413     readyTime = std::max(curTick(), targets->front().readyTime);
 414
 415     return true;
 416 }
 417
 418
 419 void
 420 MSHR::handleFill(Packet *pkt, CacheBlk *blk)
 421 {
 422     if (!pkt->sharedAsserted()
 423         && !(hasPostInvalidate() || hasPostDowngrade())
 424         && deferredTargets->needsExclusive) {
 425         // We got an exclusive response, but we have deferred targets
 426         // which are waiting to request an exclusive copy (not because
 427         // of a pending invalidate).  This can happen if the original
 428         // request was for a read-only (non-exclusive) block, but we
 429         // got an exclusive copy anyway because of the E part of the
 430         // MOESI/MESI protocol.  Since we got the exclusive copy
 431         // there's no need to defer the targets, so move them up to
 432         // the regular target list.
 433         assert(!targets->needsExclusive);
 434         targets->needsExclusive = true;
 435         // if any of the deferred targets were upper-level cache
 436         // requests marked downstreamPending, need to clear that
 437         assert(!downstreamPending);  // not pending here anymore
 438         deferredTargets->clearDownstreamPending();
 439         // this clears out deferredTargets too
 440         targets->splice(targets->end(), *deferredTargets);
 441         deferredTargets->resetFlags();
 442     }
 443 }
 444
 445
 446 bool
 447 MSHR::checkFunctional(PacketPtr pkt)
 448 {
 449     // For printing, we treat the MSHR as a whole as single entity.
 450     // For other requests, we iterate over the individual targets
 451     // since that's where the actual data lies.
 452     if (pkt->isPrint()) {
 453         pkt->checkFunctional(this, addr, size, NULL);
 454         return false;
 455     } else {
 456         return (targets->checkFunctional(pkt) ||
 457                 deferredTargets->checkFunctional(pkt));
 458     }
 459 }
 460
 461
 462 void
 463 MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
 464 {
 465     ccprintf(os, "%s[%x:%x] %s %s %s state: %s %s %s %s\n",
 466              prefix, addr, addr+size-1,
 467              isForward ? "Forward" : "",
 468              isForwardNoResponse() ? "ForwNoResp" : "",
 469              needsExclusive() ? "Excl" : "",
 470              _isUncacheable ? "Unc" : "",
 471              inService ? "InSvc" : "",
 472              downstreamPending ? "DwnPend" : "",
 473              hasPostInvalidate() ? "PostInv" : "",
 474              hasPostDowngrade() ? "PostDowngr" : "");
 475
 476     ccprintf(os, "%s  Targets:\n", prefix);
 477     targets->print(os, verbosity, prefix + "    ");
 478     if (!deferredTargets->empty()) {
 479         ccprintf(os, "%s  Deferred Targets:\n", prefix);
 480         deferredTargets->print(os, verbosity, prefix + "      ");
 481     }
 482 }
 483
 484 std::string
 485 MSHR::print() const
 486 {
 487     ostringstream str;
 488     print(str);
 489     return str.str();
 490 }
 491
 492 MSHR::~MSHR()
 493 {
 494     delete[] targets;
 495     delete[] deferredTargets;
 496 }