src/mem/cache/mshr.cc

   1 /*
   2  * Copyright (c) 2002-2005 The Regents of The University of Michigan
   3  * Copyright (c) 2010 Advanced Micro Devices, Inc.
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions are
   8  * met: redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer;
  10  * redistributions in binary form must reproduce the above copyright
  11  * notice, this list of conditions and the following disclaimer in the
  12  * documentation and/or other materials provided with the distribution;
  13  * neither the name of the copyright holders nor the names of its
  14  * contributors may be used to endorse or promote products derived from
  15  * this software without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  18  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  19  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  20  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  21  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  22  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  23  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  24  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  25  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  26  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  27  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  28  *
  29  * Authors: Erik Hallnor
  30  *          Dave Greene
  31  */
  32
  33 /**
  34  * @file
  35  * Miss Status and Handling Register (MSHR) definitions.
  36  */
  37
  38 #include <algorithm>
  39 #include <cassert>
  40 #include <string>
  41 #include <vector>
  42
  43 #include "base/misc.hh"
  44 #include "base/types.hh"
  45 #include "mem/cache/cache.hh"
  46 #include "mem/cache/mshr.hh"
  47 #include "sim/core.hh"
  48
  49 using namespace std;
  50
  51 MSHR::MSHR()
  52 {
  53     inService = false;
  54     ntargets = 0;
  55     threadNum = InvalidThreadID;
  56     targets = new TargetList();
  57     deferredTargets = new TargetList();
  58 }
  59
  60
  61 MSHR::TargetList::TargetList()
  62     : needsExclusive(false), hasUpgrade(false)
  63 {}
  64
  65
  66 inline void
  67 MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
  68                       Counter order, Target::Source source, bool markPending)
  69 {
  70     if (source != Target::FromSnoop) {
  71         if (pkt->needsExclusive()) {
  72             needsExclusive = true;
  73         }
  74
  75         // StoreCondReq is effectively an upgrade if it's in an MSHR
  76         // since it would have been failed already if we didn't have a
  77         // read-only copy
  78         if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
  79             hasUpgrade = true;
  80         }
  81     }
  82
  83     if (markPending) {
  84         MSHR *mshr = dynamic_cast<MSHR*>(pkt->senderState);
  85         if (mshr != NULL) {
  86             assert(!mshr->downstreamPending);
  87             mshr->downstreamPending = true;
  88         }
  89     }
  90
  91     push_back(Target(pkt, readyTime, order, source, markPending));
  92 }
  93
  94
  95 static void
  96 replaceUpgrade(PacketPtr pkt)
  97 {
  98     if (pkt->cmd == MemCmd::UpgradeReq) {
  99         pkt->cmd = MemCmd::ReadExReq;
 100         DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
 101     } else if (pkt->cmd == MemCmd::SCUpgradeReq) {
 102         pkt->cmd = MemCmd::SCUpgradeFailReq;
 103         DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
 104     } else if (pkt->cmd == MemCmd::StoreCondReq) {
 105         pkt->cmd = MemCmd::StoreCondFailReq;
 106         DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
 107     }
 108 }
 109
 110
 111 void
 112 MSHR::TargetList::replaceUpgrades()
 113 {
 114     if (!hasUpgrade)
 115         return;
 116
 117     Iterator end_i = end();
 118     for (Iterator i = begin(); i != end_i; ++i) {
 119         replaceUpgrade(i->pkt);
 120     }
 121
 122     hasUpgrade = false;
 123 }
 124
 125
 126 void
 127 MSHR::TargetList::clearDownstreamPending()
 128 {
 129     Iterator end_i = end();
 130     for (Iterator i = begin(); i != end_i; ++i) {
 131         if (i->markedPending) {
 132             MSHR *mshr = dynamic_cast<MSHR*>(i->pkt->senderState);
 133             if (mshr != NULL) {
 134                 mshr->clearDownstreamPending();
 135             }
 136         }
 137     }
 138 }
 139
 140
 141 bool
 142 MSHR::TargetList::checkFunctional(PacketPtr pkt)
 143 {
 144     Iterator end_i = end();
 145     for (Iterator i = begin(); i != end_i; ++i) {
 146         if (pkt->checkFunctional(i->pkt)) {
 147             return true;
 148         }
 149     }
 150
 151     return false;
 152 }
 153
 154
 155 void
 156 MSHR::TargetList::
 157 print(std::ostream &os, int verbosity, const std::string &prefix) const
 158 {
 159     ConstIterator end_i = end();
 160     for (ConstIterator i = begin(); i != end_i; ++i) {
 161         const char *s;
 162         switch (i->source) {
 163           case Target::FromCPU: s = "FromCPU";
 164           case Target::FromSnoop: s = "FromSnoop";
 165           case Target::FromPrefetcher: s = "FromPrefetcher";
 166           default: s = "";
 167         }
 168         ccprintf(os, "%s%s: ", prefix, s);
 169         i->pkt->print(os, verbosity, "");
 170     }
 171 }
 172
 173
 174 void
 175 MSHR::allocate(Addr _addr, int _size, PacketPtr target,
 176                Tick whenReady, Counter _order)
 177 {
 178     addr = _addr;
 179     size = _size;
 180     readyTime = whenReady;
 181     order = _order;
 182     assert(target);
 183     isForward = false;
 184     _isUncacheable = target->req->isUncacheable();
 185     inService = false;
 186     downstreamPending = false;
 187     threadNum = 0;
 188     ntargets = 1;
 189     assert(targets->isReset());
 190     // Don't know of a case where we would allocate a new MSHR for a
 191     // snoop (mem-side request), so set source according to request here
 192     Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
 193         Target::FromPrefetcher : Target::FromCPU;
 194     targets->add(target, whenReady, _order, source, true);
 195     assert(deferredTargets->isReset());
 196     data = NULL;
 197 }
 198
 199
 200 void
 201 MSHR::clearDownstreamPending()
 202 {
 203     assert(downstreamPending);
 204     downstreamPending = false;
 205     // recursively clear flag on any MSHRs we will be forwarding
 206     // responses to
 207     targets->clearDownstreamPending();
 208 }
 209
 210 bool
 211 MSHR::markInService(PacketPtr pkt)
 212 {
 213     assert(!inService);
 214     if (isForwardNoResponse()) {
 215         // we just forwarded the request packet & don't expect a
 216         // response, so get rid of it
 217         assert(getNumTargets() == 1);
 218         popTarget();
 219         return true;
 220     }
 221     inService = true;
 222     pendingDirty = (targets->needsExclusive ||
 223                     (!pkt->sharedAsserted() && pkt->memInhibitAsserted()));
 224     postInvalidate = postDowngrade = false;
 225
 226     if (!downstreamPending) {
 227         // let upstream caches know that the request has made it to a
 228         // level where it's going to get a response
 229         targets->clearDownstreamPending();
 230     }
 231     return false;
 232 }
 233
 234
 235 void
 236 MSHR::deallocate()
 237 {
 238     assert(targets->empty());
 239     targets->resetFlags();
 240     assert(deferredTargets->isReset());
 241     assert(ntargets == 0);
 242     inService = false;
 243 }
 244
 245 /*
 246  * Adds a target to an MSHR
 247  */
 248 void
 249 MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order)
 250 {
 251     // if there's a request already in service for this MSHR, we will
 252     // have to defer the new target until after the response if any of
 253     // the following are true:
 254     // - there are other targets already deferred
 255     // - there's a pending invalidate to be applied after the response
 256     //   comes back (but before this target is processed)
 257     // - this target requires an exclusive block and either we're not
 258     //   getting an exclusive block back or we have already snooped
 259     //   another read request that will downgrade our exclusive block
 260     //   to shared
 261
 262     // assume we'd never issue a prefetch when we've got an
 263     // outstanding miss
 264     assert(pkt->cmd != MemCmd::HardPFReq);
 265
 266     if (inService &&
 267         (!deferredTargets->empty() || hasPostInvalidate() ||
 268          (pkt->needsExclusive() &&
 269           (!isPendingDirty() || hasPostDowngrade() || isForward)))) {
 270         // need to put on deferred list
 271         if (hasPostInvalidate())
 272             replaceUpgrade(pkt);
 273         deferredTargets->add(pkt, whenReady, _order, Target::FromCPU, true);
 274     } else {
 275         // No request outstanding, or still OK to append to
 276         // outstanding request: append to regular target list.  Only
 277         // mark pending if current request hasn't been issued yet
 278         // (isn't in service).
 279         targets->add(pkt, whenReady, _order, Target::FromCPU, !inService);
 280     }
 281
 282     ++ntargets;
 283 }
 284
 285 bool
 286 MSHR::handleSnoop(PacketPtr pkt, Counter _order)
 287 {
 288     if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
 289         // Request has not been issued yet, or it's been issued
 290         // locally but is buffered unissued at some downstream cache
 291         // which is forwarding us this snoop.  Either way, the packet
 292         // we're snooping logically precedes this MSHR's request, so
 293         // the snoop has no impact on the MSHR, but must be processed
 294         // in the standard way by the cache.  The only exception is
 295         // that if we're an L2+ cache buffering an UpgradeReq from a
 296         // higher-level cache, and the snoop is invalidating, then our
 297         // buffered upgrades must be converted to read exclusives,
 298         // since the upper-level cache no longer has a valid copy.
 299         // That is, even though the upper-level cache got out on its
 300         // local bus first, some other invalidating transaction
 301         // reached the global bus before the upgrade did.
 302         if (pkt->needsExclusive()) {
 303             targets->replaceUpgrades();
 304             deferredTargets->replaceUpgrades();
 305         }
 306
 307         return false;
 308     }
 309
 310     // From here on down, the request issued by this MSHR logically
 311     // precedes the request we're snooping.
 312     if (pkt->needsExclusive()) {
 313         // snooped request still precedes the re-request we'll have to
 314         // issue for deferred targets, if any...
 315         deferredTargets->replaceUpgrades();
 316     }
 317
 318     if (hasPostInvalidate()) {
 319         // a prior snoop has already appended an invalidation, so
 320         // logically we don't have the block anymore; no need for
 321         // further snooping.
 322         return true;
 323     }
 324
 325     if (isPendingDirty() || pkt->isInvalidate()) {
 326         // We need to save and replay the packet in two cases:
 327         // 1. We're awaiting an exclusive copy, so ownership is pending,
 328         //    and we need to respond after we receive data.
 329         // 2. It's an invalidation (e.g., UpgradeReq), and we need
 330         //    to forward the snoop up the hierarchy after the current
 331         //    transaction completes.
 332
 333         // Actual target device (typ. PhysicalMemory) will delete the
 334         // packet on reception, so we need to save a copy here.
 335         PacketPtr cp_pkt = new Packet(pkt, true);
 336         targets->add(cp_pkt, curTick(), _order, Target::FromSnoop,
 337                      downstreamPending && targets->needsExclusive);
 338         ++ntargets;
 339
 340         if (isPendingDirty()) {
 341             pkt->assertMemInhibit();
 342             pkt->setSupplyExclusive();
 343         }
 344
 345         if (pkt->needsExclusive()) {
 346             // This transaction will take away our pending copy
 347             postInvalidate = true;
 348         }
 349     }
 350
 351     if (!pkt->needsExclusive()) {
 352         // This transaction will get a read-shared copy, downgrading
 353         // our copy if we had an exclusive one
 354         postDowngrade = true;
 355         pkt->assertShared();
 356     }
 357
 358     return true;
 359 }
 360
 361
 362 bool
 363 MSHR::promoteDeferredTargets()
 364 {
 365     assert(targets->empty());
 366     if (deferredTargets->empty()) {
 367         return false;
 368     }
 369
 370     // swap targets & deferredTargets lists
 371     TargetList *tmp = targets;
 372     targets = deferredTargets;
 373     deferredTargets = tmp;
 374
 375     assert(targets->size() == ntargets);
 376
 377     // clear deferredTargets flags
 378     deferredTargets->resetFlags();
 379
 380     order = targets->front().order;
 381     readyTime = std::max(curTick(), targets->front().readyTime);
 382
 383     return true;
 384 }
 385
 386
 387 void
 388 MSHR::handleFill(Packet *pkt, CacheBlk *blk)
 389 {
 390     if (!pkt->sharedAsserted()
 391         && !(hasPostInvalidate() || hasPostDowngrade())
 392         && deferredTargets->needsExclusive) {
 393         // We got an exclusive response, but we have deferred targets
 394         // which are waiting to request an exclusive copy (not because
 395         // of a pending invalidate).  This can happen if the original
 396         // request was for a read-only (non-exclusive) block, but we
 397         // got an exclusive copy anyway because of the E part of the
 398         // MOESI/MESI protocol.  Since we got the exclusive copy
 399         // there's no need to defer the targets, so move them up to
 400         // the regular target list.
 401         assert(!targets->needsExclusive);
 402         targets->needsExclusive = true;
 403         // if any of the deferred targets were upper-level cache
 404         // requests marked downstreamPending, need to clear that
 405         assert(!downstreamPending);  // not pending here anymore
 406         deferredTargets->clearDownstreamPending();
 407         // this clears out deferredTargets too
 408         targets->splice(targets->end(), *deferredTargets);
 409         deferredTargets->resetFlags();
 410     }
 411 }
 412
 413
 414 bool
 415 MSHR::checkFunctional(PacketPtr pkt)
 416 {
 417     // For printing, we treat the MSHR as a whole as single entity.
 418     // For other requests, we iterate over the individual targets
 419     // since that's where the actual data lies.
 420     if (pkt->isPrint()) {
 421         pkt->checkFunctional(this, addr, size, NULL);
 422         return false;
 423     } else {
 424         return (targets->checkFunctional(pkt) ||
 425                 deferredTargets->checkFunctional(pkt));
 426     }
 427 }
 428
 429
 430 void
 431 MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
 432 {
 433     ccprintf(os, "%s[%x:%x] %s %s %s state: %s %s %s %s\n",
 434              prefix, addr, addr+size-1,
 435              isForward ? "Forward" : "",
 436              isForwardNoResponse() ? "ForwNoResp" : "",
 437              needsExclusive() ? "Excl" : "",
 438              _isUncacheable ? "Unc" : "",
 439              inService ? "InSvc" : "",
 440              downstreamPending ? "DwnPend" : "",
 441              hasPostInvalidate() ? "PostInv" : "",
 442              hasPostDowngrade() ? "PostDowngr" : "");
 443
 444     ccprintf(os, "%s  Targets:\n", prefix);
 445     targets->print(os, verbosity, prefix + "    ");
 446     if (!deferredTargets->empty()) {
 447         ccprintf(os, "%s  Deferred Targets:\n", prefix);
 448         deferredTargets->print(os, verbosity, prefix + "      ");
 449     }
 450 }
 451
 452 MSHR::~MSHR()
 453 {
 454 }