src/mem/cache/mshr.cc - arm/gem5 - Git at Google

 /*
  * Copyright (c) 2012-2013, 2015-2018 ARM Limited
  * All rights reserved.
  *
  * The license below extends only to copyright in the software and shall
  * not be construed as granting a license to any other intellectual
  * property including but not limited to intellectual property relating
  * to a hardware implementation of the functionality of the software
  * licensed hereunder.  You may use the software subject to the license
  * terms below provided that you ensure that this notice is replicated
  * unmodified and in its entirety in all distributions of the software,
  * modified or unmodified, in source code or in binary form.
  *
  * Copyright (c) 2002-2005 The Regents of The University of Michigan
  * Copyright (c) 2010 Advanced Micro Devices, Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met: redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer;
  * redistributions in binary form must reproduce the above copyright
  * notice, this list of conditions and the following disclaimer in the
  * documentation and/or other materials provided with the distribution;
  * neither the name of the copyright holders nor the names of its
  * contributors may be used to endorse or promote products derived from
  * this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
  * Authors: Erik Hallnor
  *          Dave Greene
  */

 /**
  * @file
  * Miss Status and Handling Register (MSHR) definitions.
  */

 #include "mem/cache/mshr.hh"

 #include <algorithm>
 #include <cassert>
 #include <string>
 #include <vector>

 #include "base/logging.hh"
 #include "base/types.hh"
 #include "debug/Cache.hh"
 #include "mem/cache/cache.hh"
 #include "sim/core.hh"

 using namespace std;

 MSHR::MSHR() : downstreamPending(false),
                pendingModified(false),
                postInvalidate(false), postDowngrade(false),
                isForward(false)
 {
 }

 MSHR::TargetList::TargetList()
     : needsWritable(false), hasUpgrade(false), allocOnFill(false)
 {}


 void
 MSHR::TargetList::updateFlags(PacketPtr pkt, Target::Source source,
                               bool alloc_on_fill)
 {
     if (source != Target::FromSnoop) {
         if (pkt->needsWritable()) {
             needsWritable = true;
         }

         // StoreCondReq is effectively an upgrade if it's in an MSHR
         // since it would have been failed already if we didn't have a
         // read-only copy
         if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
             hasUpgrade = true;
         }

         // potentially re-evaluate whether we should allocate on a fill or
         // not
         allocOnFill = allocOnFill || alloc_on_fill;
     }
 }

 void
 MSHR::TargetList::populateFlags()
 {
     resetFlags();
     for (auto& t: *this) {
         updateFlags(t.pkt, t.source, t.allocOnFill);
     }
 }

 inline void
 MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
                       Counter order, Target::Source source, bool markPending,
                       bool alloc_on_fill)
 {
     updateFlags(pkt, source, alloc_on_fill);
     if (markPending) {
         // Iterate over the SenderState stack and see if we find
         // an MSHR entry. If we do, set the downstreamPending
         // flag. Otherwise, do nothing.
         MSHR *mshr = pkt->findNextSenderState<MSHR>();
         if (mshr != nullptr) {
             assert(!mshr->downstreamPending);
             mshr->downstreamPending = true;
         } else {
             // No need to clear downstreamPending later
             markPending = false;
         }
     }

     emplace_back(pkt, readyTime, order, source, markPending, alloc_on_fill);
 }


 static void
 replaceUpgrade(PacketPtr pkt)
 {
     // remember if the current packet has data allocated
     bool has_data = pkt->hasData() || pkt->hasRespData();

     if (pkt->cmd == MemCmd::UpgradeReq) {
         pkt->cmd = MemCmd::ReadExReq;
         DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
     } else if (pkt->cmd == MemCmd::SCUpgradeReq) {
         pkt->cmd = MemCmd::SCUpgradeFailReq;
         DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
     } else if (pkt->cmd == MemCmd::StoreCondReq) {
         pkt->cmd = MemCmd::StoreCondFailReq;
         DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
     }

     if (!has_data) {
         // there is no sensible way of setting the data field if the
         // new command actually would carry data
         assert(!pkt->hasData());

         if (pkt->hasRespData()) {
             // we went from a packet that had no data (neither request,
             // nor response), to one that does, and therefore we need to
             // actually allocate space for the data payload
             pkt->allocate();
         }
     }
 }


 void
 MSHR::TargetList::replaceUpgrades()
 {
     if (!hasUpgrade)
         return;

     for (auto& t : *this) {
         replaceUpgrade(t.pkt);
     }

     hasUpgrade = false;
 }


 void
 MSHR::TargetList::clearDownstreamPending()
 {
     for (auto& t : *this) {
         if (t.markedPending) {
             // Iterate over the SenderState stack and see if we find
             // an MSHR entry. If we find one, clear the
             // downstreamPending flag by calling
             // clearDownstreamPending(). This recursively clears the
             // downstreamPending flag in all caches this packet has
             // passed through.
             MSHR *mshr = t.pkt->findNextSenderState<MSHR>();
             if (mshr != nullptr) {
                 mshr->clearDownstreamPending();
             }
             t.markedPending = false;
         }
     }
 }


 bool
 MSHR::TargetList::checkFunctional(PacketPtr pkt)
 {
     for (auto& t : *this) {
         if (pkt->checkFunctional(t.pkt)) {
             return true;
         }
     }

     return false;
 }


 void
 MSHR::TargetList::print(std::ostream &os, int verbosity,
                         const std::string &prefix) const
 {
     for (auto& t : *this) {
         const char *s;
         switch (t.source) {
           case Target::FromCPU:
             s = "FromCPU";
             break;
           case Target::FromSnoop:
             s = "FromSnoop";
             break;
           case Target::FromPrefetcher:
             s = "FromPrefetcher";
             break;
           default:
             s = "";
             break;
         }
         ccprintf(os, "%s%s: ", prefix, s);
         t.pkt->print(os, verbosity, "");
         ccprintf(os, "\n");
     }
 }


 void
 MSHR::allocate(Addr blk_addr, unsigned blk_size, PacketPtr target,
                Tick when_ready, Counter _order, bool alloc_on_fill)
 {
     blkAddr = blk_addr;
     blkSize = blk_size;
     isSecure = target->isSecure();
     readyTime = when_ready;
     order = _order;
     assert(target);
     isForward = false;
     _isUncacheable = target->req->isUncacheable();
     inService = false;
     downstreamPending = false;
     assert(targets.isReset());
     // Don't know of a case where we would allocate a new MSHR for a
     // snoop (mem-side request), so set source according to request here
     Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
         Target::FromPrefetcher : Target::FromCPU;
     targets.add(target, when_ready, _order, source, true, alloc_on_fill);
     assert(deferredTargets.isReset());
 }


 void
 MSHR::clearDownstreamPending()
 {
     assert(downstreamPending);
     downstreamPending = false;
     // recursively clear flag on any MSHRs we will be forwarding
     // responses to
     targets.clearDownstreamPending();
 }

 void
 MSHR::markInService(bool pending_modified_resp)
 {
     assert(!inService);

     inService = true;
     pendingModified = targets.needsWritable || pending_modified_resp;
     postInvalidate = postDowngrade = false;

     if (!downstreamPending) {
         // let upstream caches know that the request has made it to a
         // level where it's going to get a response
         targets.clearDownstreamPending();
     }
 }


 void
 MSHR::deallocate()
 {
     assert(targets.empty());
     targets.resetFlags();
     assert(deferredTargets.isReset());
     inService = false;
 }

 /*
  * Adds a target to an MSHR
  */
 void
 MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order,
                      bool alloc_on_fill)
 {
     // assume we'd never issue a prefetch when we've got an
     // outstanding miss
     assert(pkt->cmd != MemCmd::HardPFReq);

     // uncacheable accesses always allocate a new MSHR, and cacheable
     // accesses ignore any uncacheable MSHRs, thus we should never
     // have targets addded if originally allocated uncacheable
     assert(!_isUncacheable);

     // if there's a request already in service for this MSHR, we will
     // have to defer the new target until after the response if any of
     // the following are true:
     // - there are other targets already deferred
     // - there's a pending invalidate to be applied after the response
     //   comes back (but before this target is processed)
     // - the MSHR's first (and only) non-deferred target is a cache
     //   maintenance packet
     // - the new target is a cache maintenance packet (this is probably
     //   overly conservative but certainly safe)
     // - this target requires a writable block and either we're not
     //   getting a writable block back or we have already snooped
     //   another read request that will downgrade our writable block
     //   to non-writable (Shared or Owned)
     PacketPtr tgt_pkt = targets.front().pkt;
     if (pkt->req->isCacheMaintenance() ||
         tgt_pkt->req->isCacheMaintenance() ||
         !deferredTargets.empty() ||
         (inService &&
          (hasPostInvalidate() ||
           (pkt->needsWritable() &&
            (!isPendingModified() || hasPostDowngrade() || isForward))))) {
         // need to put on deferred list
         if (inService && hasPostInvalidate())
             replaceUpgrade(pkt);
         deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true,
                             alloc_on_fill);
     } else {
         // No request outstanding, or still OK to append to
         // outstanding request: append to regular target list.  Only
         // mark pending if current request hasn't been issued yet
         // (isn't in service).
         targets.add(pkt, whenReady, _order, Target::FromCPU, !inService,
                     alloc_on_fill);
     }
 }

 bool
 MSHR::handleSnoop(PacketPtr pkt, Counter _order)
 {
     DPRINTF(Cache, "%s for %s\n", __func__, pkt->print());

     // when we snoop packets the needsWritable and isInvalidate flags
     // should always be the same, however, this assumes that we never
     // snoop writes as they are currently not marked as invalidations
     panic_if((pkt->needsWritable() != pkt->isInvalidate()) &&
              !pkt->req->isCacheMaintenance(),
              "%s got snoop %s where needsWritable, "
              "does not match isInvalidate", name(), pkt->print());

     if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
         // Request has not been issued yet, or it's been issued
         // locally but is buffered unissued at some downstream cache
         // which is forwarding us this snoop.  Either way, the packet
         // we're snooping logically precedes this MSHR's request, so
         // the snoop has no impact on the MSHR, but must be processed
         // in the standard way by the cache.  The only exception is
         // that if we're an L2+ cache buffering an UpgradeReq from a
         // higher-level cache, and the snoop is invalidating, then our
         // buffered upgrades must be converted to read exclusives,
         // since the upper-level cache no longer has a valid copy.
         // That is, even though the upper-level cache got out on its
         // local bus first, some other invalidating transaction
         // reached the global bus before the upgrade did.
         if (pkt->needsWritable() || pkt->req->isCacheInvalidate()) {
             targets.replaceUpgrades();
             deferredTargets.replaceUpgrades();
         }

         return false;
     }

     // From here on down, the request issued by this MSHR logically
     // precedes the request we're snooping.
     if (pkt->needsWritable() || pkt->req->isCacheInvalidate()) {
         // snooped request still precedes the re-request we'll have to
         // issue for deferred targets, if any...
         deferredTargets.replaceUpgrades();
     }

     PacketPtr tgt_pkt = targets.front().pkt;
     if (hasPostInvalidate() || tgt_pkt->req->isCacheInvalidate()) {
         // a prior snoop has already appended an invalidation or a
         // cache invalidation operation is in progress, so logically
         // we don't have the block anymore; no need for further
         // snooping.
         return true;
     }

     if (isPendingModified() || pkt->isInvalidate()) {
         // We need to save and replay the packet in two cases:
         // 1. We're awaiting a writable copy (Modified or Exclusive),
         //    so this MSHR is the orgering point, and we need to respond
         //    after we receive data.
         // 2. It's an invalidation (e.g., UpgradeReq), and we need
         //    to forward the snoop up the hierarchy after the current
         //    transaction completes.

         // Start by determining if we will eventually respond or not,
         // matching the conditions checked in Cache::handleSnoop
         bool will_respond = isPendingModified() && pkt->needsResponse() &&
                       !pkt->isClean();

         // The packet we are snooping may be deleted by the time we
         // actually process the target, and we consequently need to
         // save a copy here. Clear flags and also allocate new data as
         // the original packet data storage may have been deleted by
         // the time we get to process this packet. In the cases where
         // we are not responding after handling the snoop we also need
         // to create a copy of the request to be on the safe side. In
         // the latter case the cache is responsible for deleting both
         // the packet and the request as part of handling the deferred
         // snoop.
         PacketPtr cp_pkt = will_respond ? new Packet(pkt, true, true) :
             new Packet(new Request(*pkt->req), pkt->cmd, blkSize, pkt->id);

         if (will_respond) {
             // we are the ordering point, and will consequently
             // respond, and depending on whether the packet
             // needsWritable or not we either pass a Shared line or a
             // Modified line
             pkt->setCacheResponding();

             // inform the cache hierarchy that this cache had the line
             // in the Modified state, even if the response is passed
             // as Shared (and thus non-writable)
             pkt->setResponderHadWritable();

             // in the case of an uncacheable request there is no need
             // to set the responderHadWritable flag, but since the
             // recipient does not care there is no harm in doing so
         }
         targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
                     downstreamPending && targets.needsWritable, false);

         if (pkt->needsWritable() || pkt->isInvalidate()) {
             // This transaction will take away our pending copy
             postInvalidate = true;
         }

         if (isPendingModified() && pkt->isClean()) {
             pkt->setSatisfied();
         }
     }

     if (!pkt->needsWritable() && !pkt->req->isUncacheable()) {
         // This transaction will get a read-shared copy, downgrading
         // our copy if we had a writable one
         postDowngrade = true;
         // make sure that any downstream cache does not respond with a
         // writable (and dirty) copy even if it has one, unless it was
         // explicitly asked for one
         pkt->setHasSharers();
     }

     return true;
 }

 MSHR::TargetList
 MSHR::extractServiceableTargets(PacketPtr pkt)
 {
     TargetList ready_targets;
     // If the downstream MSHR got an invalidation request then we only
     // service the first of the FromCPU targets and any other
     // non-FromCPU target. This way the remaining FromCPU targets
     // issue a new request and get a fresh copy of the block and we
     // avoid memory consistency violations.
     if (pkt->cmd == MemCmd::ReadRespWithInvalidate) {
         auto it = targets.begin();
         assert((it->source == Target::FromCPU) ||
                (it->source == Target::FromPrefetcher));
         ready_targets.push_back(*it);
         it = targets.erase(it);
         while (it != targets.end()) {
             if (it->source == Target::FromCPU) {
                 it++;
             } else {
                 assert(it->source == Target::FromSnoop);
                 ready_targets.push_back(*it);
                 it = targets.erase(it);
             }
         }
         ready_targets.populateFlags();
     } else {
         std::swap(ready_targets, targets);
     }
     targets.populateFlags();

     return ready_targets;
 }

 bool
 MSHR::promoteDeferredTargets()
 {
     if (targets.empty() && deferredTargets.empty()) {
         // nothing to promote
         return false;
     }

     // the deferred targets can be generally promoted unless they
     // contain a cache maintenance request

     // find the first target that is a cache maintenance request
     auto it = std::find_if(deferredTargets.begin(), deferredTargets.end(),
                            [](MSHR::Target &t) {
                                return t.pkt->req->isCacheMaintenance();
                            });
     if (it == deferredTargets.begin()) {
         // if the first deferred target is a cache maintenance packet
         // then we can promote provided the targets list is empty and
         // we can service it on its own
         if (targets.empty()) {
             targets.splice(targets.end(), deferredTargets, it);
         }
     } else {
         // if a cache maintenance operation exists, we promote all the
         // deferred targets that precede it, or all deferred targets
         // otherwise
         targets.splice(targets.end(), deferredTargets,
                        deferredTargets.begin(), it);
     }

     deferredTargets.populateFlags();
     targets.populateFlags();
     order = targets.front().order;
     readyTime = std::max(curTick(), targets.front().readyTime);

     return true;
 }


 void
 MSHR::promoteWritable()
 {
     if (deferredTargets.needsWritable &&
         !(hasPostInvalidate() || hasPostDowngrade())) {
         // We got a writable response, but we have deferred targets
         // which are waiting to request a writable copy (not because
         // of a pending invalidate).  This can happen if the original
         // request was for a read-only block, but we got a writable
         // response anyway. Since we got the writable copy there's no
         // need to defer the targets, so move them up to the regular
         // target list.
         assert(!targets.needsWritable);
         targets.needsWritable = true;
         // if any of the deferred targets were upper-level cache
         // requests marked downstreamPending, need to clear that
         assert(!downstreamPending);  // not pending here anymore
         deferredTargets.clearDownstreamPending();
         // this clears out deferredTargets too
         targets.splice(targets.end(), deferredTargets);
         deferredTargets.resetFlags();
     }
 }


 bool
 MSHR::checkFunctional(PacketPtr pkt)
 {
     // For printing, we treat the MSHR as a whole as single entity.
     // For other requests, we iterate over the individual targets
     // since that's where the actual data lies.
     if (pkt->isPrint()) {
         pkt->checkFunctional(this, blkAddr, isSecure, blkSize, nullptr);
         return false;
     } else {
         return (targets.checkFunctional(pkt) ||
                 deferredTargets.checkFunctional(pkt));
     }
 }

 bool
 MSHR::sendPacket(Cache &cache)
 {
     return cache.sendMSHRQueuePacket(this);
 }

 void
 MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
 {
     ccprintf(os, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
              prefix, blkAddr, blkAddr + blkSize - 1,
              isSecure ? "s" : "ns",
              isForward ? "Forward" : "",
              allocOnFill() ? "AllocOnFill" : "",
              needsWritable() ? "Wrtbl" : "",
              _isUncacheable ? "Unc" : "",
              inService ? "InSvc" : "",
              downstreamPending ? "DwnPend" : "",
              postInvalidate ? "PostInv" : "",
              postDowngrade ? "PostDowngr" : "");

     if (!targets.empty()) {
         ccprintf(os, "%s  Targets:\n", prefix);
         targets.print(os, verbosity, prefix + "    ");
     }
     if (!deferredTargets.empty()) {
         ccprintf(os, "%s  Deferred Targets:\n", prefix);
         deferredTargets.print(os, verbosity, prefix + "      ");
     }
 }

 std::string
 MSHR::print() const
 {
     ostringstream str;
     print(str);
     return str.str();
 }
	/*
	* Copyright (c) 2012-2013, 2015-2018 ARM Limited
	* All rights reserved.
	*
	* The license below extends only to copyright in the software and shall
	* not be construed as granting a license to any other intellectual
	* property including but not limited to intellectual property relating
	* to a hardware implementation of the functionality of the software
	* licensed hereunder. You may use the software subject to the license
	* terms below provided that you ensure that this notice is replicated
	* unmodified and in its entirety in all distributions of the software,
	* modified or unmodified, in source code or in binary form.
	*
	* Copyright (c) 2002-2005 The Regents of The University of Michigan
	* Copyright (c) 2010 Advanced Micro Devices, Inc.
	* All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions are
	* met: redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer;
	* redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution;
	* neither the name of the copyright holders nor the names of its
	* contributors may be used to endorse or promote products derived from
	* this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
	* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
	* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
	* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
	* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
	* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
	* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*
	* Authors: Erik Hallnor
	* Dave Greene
	*/

	/**
	* @file
	* Miss Status and Handling Register (MSHR) definitions.
	*/

	#include "mem/cache/mshr.hh"

	#include <algorithm>
	#include <cassert>
	#include <string>
	#include <vector>

	#include "base/logging.hh"
	#include "base/types.hh"
	#include "debug/Cache.hh"
	#include "mem/cache/cache.hh"
	#include "sim/core.hh"

	using namespace std;

	MSHR::MSHR() : downstreamPending(false),
	pendingModified(false),
	postInvalidate(false), postDowngrade(false),
	isForward(false)
	{
	}

	MSHR::TargetList::TargetList()
	: needsWritable(false), hasUpgrade(false), allocOnFill(false)
	{}


	void
	MSHR::TargetList::updateFlags(PacketPtr pkt, Target::Source source,
	bool alloc_on_fill)
	{
	if (source != Target::FromSnoop) {
	if (pkt->needsWritable()) {
	needsWritable = true;
	}

	// StoreCondReq is effectively an upgrade if it's in an MSHR
	// since it would have been failed already if we didn't have a
	// read-only copy
	if (pkt->isUpgrade() \|\| pkt->cmd == MemCmd::StoreCondReq) {
	hasUpgrade = true;
	}

	// potentially re-evaluate whether we should allocate on a fill or
	// not
	allocOnFill = allocOnFill \|\| alloc_on_fill;
	}
	}

	void
	MSHR::TargetList::populateFlags()
	{
	resetFlags();
	for (auto& t: *this) {
	updateFlags(t.pkt, t.source, t.allocOnFill);
	}
	}

	inline void
	MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
	Counter order, Target::Source source, bool markPending,
	bool alloc_on_fill)
	{
	updateFlags(pkt, source, alloc_on_fill);
	if (markPending) {
	// Iterate over the SenderState stack and see if we find
	// an MSHR entry. If we do, set the downstreamPending
	// flag. Otherwise, do nothing.
	MSHR *mshr = pkt->findNextSenderState<MSHR>();
	if (mshr != nullptr) {
	assert(!mshr->downstreamPending);
	mshr->downstreamPending = true;
	} else {
	// No need to clear downstreamPending later
	markPending = false;
	}
	}

	emplace_back(pkt, readyTime, order, source, markPending, alloc_on_fill);
	}


	static void
	replaceUpgrade(PacketPtr pkt)
	{
	// remember if the current packet has data allocated
	bool has_data = pkt->hasData() \|\| pkt->hasRespData();

	if (pkt->cmd == MemCmd::UpgradeReq) {
	pkt->cmd = MemCmd::ReadExReq;
	DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
	} else if (pkt->cmd == MemCmd::SCUpgradeReq) {
	pkt->cmd = MemCmd::SCUpgradeFailReq;
	DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
	} else if (pkt->cmd == MemCmd::StoreCondReq) {
	pkt->cmd = MemCmd::StoreCondFailReq;
	DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
	}

	if (!has_data) {
	// there is no sensible way of setting the data field if the
	// new command actually would carry data
	assert(!pkt->hasData());

	if (pkt->hasRespData()) {
	// we went from a packet that had no data (neither request,
	// nor response), to one that does, and therefore we need to
	// actually allocate space for the data payload
	pkt->allocate();
	}
	}
	}


	void
	MSHR::TargetList::replaceUpgrades()
	{
	if (!hasUpgrade)
	return;

	for (auto& t : *this) {
	replaceUpgrade(t.pkt);
	}

	hasUpgrade = false;
	}


	void
	MSHR::TargetList::clearDownstreamPending()
	{
	for (auto& t : *this) {
	if (t.markedPending) {
	// Iterate over the SenderState stack and see if we find
	// an MSHR entry. If we find one, clear the
	// downstreamPending flag by calling
	// clearDownstreamPending(). This recursively clears the
	// downstreamPending flag in all caches this packet has
	// passed through.
	MSHR *mshr = t.pkt->findNextSenderState<MSHR>();
	if (mshr != nullptr) {
	mshr->clearDownstreamPending();
	}
	t.markedPending = false;
	}
	}
	}


	bool
	MSHR::TargetList::checkFunctional(PacketPtr pkt)
	{
	for (auto& t : *this) {
	if (pkt->checkFunctional(t.pkt)) {
	return true;
	}
	}

	return false;
	}


	void
	MSHR::TargetList::print(std::ostream &os, int verbosity,
	const std::string &prefix) const
	{
	for (auto& t : *this) {
	const char *s;
	switch (t.source) {
	case Target::FromCPU:
	s = "FromCPU";
	break;
	case Target::FromSnoop:
	s = "FromSnoop";
	break;
	case Target::FromPrefetcher:
	s = "FromPrefetcher";
	break;
	default:
	s = "";
	break;
	}
	ccprintf(os, "%s%s: ", prefix, s);
	t.pkt->print(os, verbosity, "");
	ccprintf(os, "\n");
	}
	}


	void
	MSHR::allocate(Addr blk_addr, unsigned blk_size, PacketPtr target,
	Tick when_ready, Counter _order, bool alloc_on_fill)
	{
	blkAddr = blk_addr;
	blkSize = blk_size;
	isSecure = target->isSecure();
	readyTime = when_ready;
	order = _order;
	assert(target);
	isForward = false;
	_isUncacheable = target->req->isUncacheable();
	inService = false;
	downstreamPending = false;
	assert(targets.isReset());
	// Don't know of a case where we would allocate a new MSHR for a
	// snoop (mem-side request), so set source according to request here
	Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
	Target::FromPrefetcher : Target::FromCPU;
	targets.add(target, when_ready, _order, source, true, alloc_on_fill);
	assert(deferredTargets.isReset());
	}


	void
	MSHR::clearDownstreamPending()
	{
	assert(downstreamPending);
	downstreamPending = false;
	// recursively clear flag on any MSHRs we will be forwarding
	// responses to
	targets.clearDownstreamPending();
	}

	void
	MSHR::markInService(bool pending_modified_resp)
	{
	assert(!inService);

	inService = true;
	pendingModified = targets.needsWritable \|\| pending_modified_resp;
	postInvalidate = postDowngrade = false;

	if (!downstreamPending) {
	// let upstream caches know that the request has made it to a
	// level where it's going to get a response
	targets.clearDownstreamPending();
	}
	}


	void
	MSHR::deallocate()
	{
	assert(targets.empty());
	targets.resetFlags();
	assert(deferredTargets.isReset());
	inService = false;
	}

	/*
	* Adds a target to an MSHR
	*/
	void
	MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order,
	bool alloc_on_fill)
	{
	// assume we'd never issue a prefetch when we've got an
	// outstanding miss
	assert(pkt->cmd != MemCmd::HardPFReq);

	// uncacheable accesses always allocate a new MSHR, and cacheable
	// accesses ignore any uncacheable MSHRs, thus we should never
	// have targets addded if originally allocated uncacheable
	assert(!_isUncacheable);

	// if there's a request already in service for this MSHR, we will
	// have to defer the new target until after the response if any of
	// the following are true:
	// - there are other targets already deferred
	// - there's a pending invalidate to be applied after the response
	// comes back (but before this target is processed)
	// - the MSHR's first (and only) non-deferred target is a cache
	// maintenance packet
	// - the new target is a cache maintenance packet (this is probably
	// overly conservative but certainly safe)
	// - this target requires a writable block and either we're not
	// getting a writable block back or we have already snooped
	// another read request that will downgrade our writable block
	// to non-writable (Shared or Owned)
	PacketPtr tgt_pkt = targets.front().pkt;
	if (pkt->req->isCacheMaintenance() \|\|
	tgt_pkt->req->isCacheMaintenance() \|\|
	!deferredTargets.empty() \|\|
	(inService &&
	(hasPostInvalidate() \|\|
	(pkt->needsWritable() &&
	(!isPendingModified() \|\| hasPostDowngrade() \|\| isForward))))) {
	// need to put on deferred list
	if (inService && hasPostInvalidate())
	replaceUpgrade(pkt);
	deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true,
	alloc_on_fill);
	} else {
	// No request outstanding, or still OK to append to
	// outstanding request: append to regular target list. Only
	// mark pending if current request hasn't been issued yet
	// (isn't in service).
	targets.add(pkt, whenReady, _order, Target::FromCPU, !inService,
	alloc_on_fill);
	}
	}

	bool
	MSHR::handleSnoop(PacketPtr pkt, Counter _order)
	{
	DPRINTF(Cache, "%s for %s\n", __func__, pkt->print());

	// when we snoop packets the needsWritable and isInvalidate flags
	// should always be the same, however, this assumes that we never
	// snoop writes as they are currently not marked as invalidations
	panic_if((pkt->needsWritable() != pkt->isInvalidate()) &&
	!pkt->req->isCacheMaintenance(),
	"%s got snoop %s where needsWritable, "
	"does not match isInvalidate", name(), pkt->print());

	if (!inService \|\| (pkt->isExpressSnoop() && downstreamPending)) {
	// Request has not been issued yet, or it's been issued
	// locally but is buffered unissued at some downstream cache
	// which is forwarding us this snoop. Either way, the packet
	// we're snooping logically precedes this MSHR's request, so
	// the snoop has no impact on the MSHR, but must be processed
	// in the standard way by the cache. The only exception is
	// that if we're an L2+ cache buffering an UpgradeReq from a
	// higher-level cache, and the snoop is invalidating, then our
	// buffered upgrades must be converted to read exclusives,
	// since the upper-level cache no longer has a valid copy.
	// That is, even though the upper-level cache got out on its
	// local bus first, some other invalidating transaction
	// reached the global bus before the upgrade did.
	if (pkt->needsWritable() \|\| pkt->req->isCacheInvalidate()) {
	targets.replaceUpgrades();
	deferredTargets.replaceUpgrades();
	}

	return false;
	}

	// From here on down, the request issued by this MSHR logically
	// precedes the request we're snooping.
	if (pkt->needsWritable() \|\| pkt->req->isCacheInvalidate()) {
	// snooped request still precedes the re-request we'll have to
	// issue for deferred targets, if any...
	deferredTargets.replaceUpgrades();
	}

	PacketPtr tgt_pkt = targets.front().pkt;
	if (hasPostInvalidate() \|\| tgt_pkt->req->isCacheInvalidate()) {
	// a prior snoop has already appended an invalidation or a
	// cache invalidation operation is in progress, so logically
	// we don't have the block anymore; no need for further
	// snooping.
	return true;
	}

	if (isPendingModified() \|\| pkt->isInvalidate()) {
	// We need to save and replay the packet in two cases:
	// 1. We're awaiting a writable copy (Modified or Exclusive),
	// so this MSHR is the orgering point, and we need to respond
	// after we receive data.
	// 2. It's an invalidation (e.g., UpgradeReq), and we need
	// to forward the snoop up the hierarchy after the current
	// transaction completes.

	// Start by determining if we will eventually respond or not,
	// matching the conditions checked in Cache::handleSnoop
	bool will_respond = isPendingModified() && pkt->needsResponse() &&
	!pkt->isClean();

	// The packet we are snooping may be deleted by the time we
	// actually process the target, and we consequently need to
	// save a copy here. Clear flags and also allocate new data as
	// the original packet data storage may have been deleted by
	// the time we get to process this packet. In the cases where
	// we are not responding after handling the snoop we also need
	// to create a copy of the request to be on the safe side. In
	// the latter case the cache is responsible for deleting both
	// the packet and the request as part of handling the deferred
	// snoop.
	PacketPtr cp_pkt = will_respond ? new Packet(pkt, true, true) :
	new Packet(new Request(*pkt->req), pkt->cmd, blkSize, pkt->id);

	if (will_respond) {
	// we are the ordering point, and will consequently
	// respond, and depending on whether the packet
	// needsWritable or not we either pass a Shared line or a
	// Modified line
	pkt->setCacheResponding();

	// inform the cache hierarchy that this cache had the line
	// in the Modified state, even if the response is passed
	// as Shared (and thus non-writable)
	pkt->setResponderHadWritable();

	// in the case of an uncacheable request there is no need
	// to set the responderHadWritable flag, but since the
	// recipient does not care there is no harm in doing so
	}
	targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
	downstreamPending && targets.needsWritable, false);

	if (pkt->needsWritable() \|\| pkt->isInvalidate()) {
	// This transaction will take away our pending copy
	postInvalidate = true;
	}

	if (isPendingModified() && pkt->isClean()) {
	pkt->setSatisfied();
	}
	}

	if (!pkt->needsWritable() && !pkt->req->isUncacheable()) {
	// This transaction will get a read-shared copy, downgrading
	// our copy if we had a writable one
	postDowngrade = true;
	// make sure that any downstream cache does not respond with a
	// writable (and dirty) copy even if it has one, unless it was
	// explicitly asked for one
	pkt->setHasSharers();
	}

	return true;
	}

	MSHR::TargetList
	MSHR::extractServiceableTargets(PacketPtr pkt)
	{
	TargetList ready_targets;
	// If the downstream MSHR got an invalidation request then we only
	// service the first of the FromCPU targets and any other
	// non-FromCPU target. This way the remaining FromCPU targets
	// issue a new request and get a fresh copy of the block and we
	// avoid memory consistency violations.
	if (pkt->cmd == MemCmd::ReadRespWithInvalidate) {
	auto it = targets.begin();
	assert((it->source == Target::FromCPU) \|\|
	(it->source == Target::FromPrefetcher));
	ready_targets.push_back(*it);
	it = targets.erase(it);
	while (it != targets.end()) {
	if (it->source == Target::FromCPU) {
	it++;
	} else {
	assert(it->source == Target::FromSnoop);
	ready_targets.push_back(*it);
	it = targets.erase(it);
	}
	}
	ready_targets.populateFlags();
	} else {
	std::swap(ready_targets, targets);
	}
	targets.populateFlags();

	return ready_targets;
	}

	bool
	MSHR::promoteDeferredTargets()
	{
	if (targets.empty() && deferredTargets.empty()) {
	// nothing to promote
	return false;
	}

	// the deferred targets can be generally promoted unless they
	// contain a cache maintenance request

	// find the first target that is a cache maintenance request
	auto it = std::find_if(deferredTargets.begin(), deferredTargets.end(),
	[](MSHR::Target &t) {
	return t.pkt->req->isCacheMaintenance();
	});
	if (it == deferredTargets.begin()) {
	// if the first deferred target is a cache maintenance packet
	// then we can promote provided the targets list is empty and
	// we can service it on its own
	if (targets.empty()) {
	targets.splice(targets.end(), deferredTargets, it);
	}
	} else {
	// if a cache maintenance operation exists, we promote all the
	// deferred targets that precede it, or all deferred targets
	// otherwise
	targets.splice(targets.end(), deferredTargets,
	deferredTargets.begin(), it);
	}

	deferredTargets.populateFlags();
	targets.populateFlags();
	order = targets.front().order;
	readyTime = std::max(curTick(), targets.front().readyTime);

	return true;
	}


	void
	MSHR::promoteWritable()
	{
	if (deferredTargets.needsWritable &&
	!(hasPostInvalidate() \|\| hasPostDowngrade())) {
	// We got a writable response, but we have deferred targets
	// which are waiting to request a writable copy (not because
	// of a pending invalidate). This can happen if the original
	// request was for a read-only block, but we got a writable
	// response anyway. Since we got the writable copy there's no
	// need to defer the targets, so move them up to the regular
	// target list.
	assert(!targets.needsWritable);
	targets.needsWritable = true;
	// if any of the deferred targets were upper-level cache
	// requests marked downstreamPending, need to clear that
	assert(!downstreamPending); // not pending here anymore
	deferredTargets.clearDownstreamPending();
	// this clears out deferredTargets too
	targets.splice(targets.end(), deferredTargets);
	deferredTargets.resetFlags();
	}
	}


	bool
	MSHR::checkFunctional(PacketPtr pkt)
	{
	// For printing, we treat the MSHR as a whole as single entity.
	// For other requests, we iterate over the individual targets
	// since that's where the actual data lies.
	if (pkt->isPrint()) {
	pkt->checkFunctional(this, blkAddr, isSecure, blkSize, nullptr);
	return false;
	} else {
	return (targets.checkFunctional(pkt) \|\|
	deferredTargets.checkFunctional(pkt));
	}
	}

	bool
	MSHR::sendPacket(Cache &cache)
	{
	return cache.sendMSHRQueuePacket(this);
	}

	void
	MSHR::print(std::ostream &os, int verbosity, const std::string &prefix) const
	{
	ccprintf(os, "%s[%#llx:%#llx](%s) %s %s %s state: %s %s %s %s %s\n",
	prefix, blkAddr, blkAddr + blkSize - 1,
	isSecure ? "s" : "ns",
	isForward ? "Forward" : "",
	allocOnFill() ? "AllocOnFill" : "",
	needsWritable() ? "Wrtbl" : "",
	_isUncacheable ? "Unc" : "",
	inService ? "InSvc" : "",
	downstreamPending ? "DwnPend" : "",
	postInvalidate ? "PostInv" : "",
	postDowngrade ? "PostDowngr" : "");

	if (!targets.empty()) {
	ccprintf(os, "%s Targets:\n", prefix);
	targets.print(os, verbosity, prefix + " ");
	}
	if (!deferredTargets.empty()) {
	ccprintf(os, "%s Deferred Targets:\n", prefix);
	deferredTargets.print(os, verbosity, prefix + " ");
	}
	}

	std::string
	MSHR::print() const
	{
	ostringstream str;
	print(str);
	return str.str();
	}