0bd9dfb8de
A response to a ReadReq can either be a ReadResp or a ReadRespWithInvalidate. As we add targets to an MSHR for a ReadReq we assume that the response will be a ReadResp. When the response is invalidating (ReadRespWithInvalidate) servicing more than one targets can potentially violate the memory ordering. This change fixes the way we handle a ReadRespWithInvalidate. When a cache receives a ReadRespWithInvalidate we service only the first FromCPU target and all the FromSnoop targets from the MSHR target list. The rest of the FromCPU targets are deferred and serviced by a new request. Change-Id: I75c30c268851987ee5f8644acb46f440b4eeeec2 Reviewed-by: Andreas Hansson <andreas.hansson@arm.com> Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
596 lines
20 KiB
C++
596 lines
20 KiB
C++
/*
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* Copyright (c) 2012-2013, 2015-2016 ARM Limited
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* All rights reserved.
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*
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* The license below extends only to copyright in the software and shall
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* not be construed as granting a license to any other intellectual
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* property including but not limited to intellectual property relating
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* to a hardware implementation of the functionality of the software
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* licensed hereunder. You may use the software subject to the license
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* terms below provided that you ensure that this notice is replicated
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* unmodified and in its entirety in all distributions of the software,
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* modified or unmodified, in source code or in binary form.
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*
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* Copyright (c) 2002-2005 The Regents of The University of Michigan
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* Copyright (c) 2010 Advanced Micro Devices, Inc.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Authors: Erik Hallnor
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* Dave Greene
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*/
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/**
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* @file
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* Miss Status and Handling Register (MSHR) definitions.
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*/
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#include "mem/cache/mshr.hh"
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#include <algorithm>
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#include <cassert>
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#include <string>
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#include <vector>
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#include "base/misc.hh"
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#include "base/types.hh"
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#include "debug/Cache.hh"
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#include "mem/cache/cache.hh"
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#include "sim/core.hh"
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using namespace std;
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MSHR::MSHR() : downstreamPending(false),
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pendingModified(false),
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postInvalidate(false), postDowngrade(false),
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isForward(false)
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{
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}
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MSHR::TargetList::TargetList()
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: needsWritable(false), hasUpgrade(false), allocOnFill(false)
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{}
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void
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MSHR::TargetList::updateFlags(PacketPtr pkt, Target::Source source,
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bool alloc_on_fill)
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{
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if (source != Target::FromSnoop) {
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if (pkt->needsWritable()) {
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needsWritable = true;
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}
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// StoreCondReq is effectively an upgrade if it's in an MSHR
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// since it would have been failed already if we didn't have a
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// read-only copy
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if (pkt->isUpgrade() || pkt->cmd == MemCmd::StoreCondReq) {
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hasUpgrade = true;
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}
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// potentially re-evaluate whether we should allocate on a fill or
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// not
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allocOnFill = allocOnFill || alloc_on_fill;
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}
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}
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void
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MSHR::TargetList::populateFlags()
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{
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resetFlags();
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for (auto& t: *this) {
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updateFlags(t.pkt, t.source, t.allocOnFill);
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}
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}
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inline void
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MSHR::TargetList::add(PacketPtr pkt, Tick readyTime,
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Counter order, Target::Source source, bool markPending,
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bool alloc_on_fill)
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{
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updateFlags(pkt, source, alloc_on_fill);
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if (markPending) {
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// Iterate over the SenderState stack and see if we find
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// an MSHR entry. If we do, set the downstreamPending
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// flag. Otherwise, do nothing.
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MSHR *mshr = pkt->findNextSenderState<MSHR>();
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if (mshr != nullptr) {
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assert(!mshr->downstreamPending);
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mshr->downstreamPending = true;
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} else {
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// No need to clear downstreamPending later
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markPending = false;
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}
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}
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emplace_back(pkt, readyTime, order, source, markPending, alloc_on_fill);
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}
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static void
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replaceUpgrade(PacketPtr pkt)
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{
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// remember if the current packet has data allocated
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bool has_data = pkt->hasData() || pkt->hasRespData();
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if (pkt->cmd == MemCmd::UpgradeReq) {
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pkt->cmd = MemCmd::ReadExReq;
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DPRINTF(Cache, "Replacing UpgradeReq with ReadExReq\n");
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} else if (pkt->cmd == MemCmd::SCUpgradeReq) {
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pkt->cmd = MemCmd::SCUpgradeFailReq;
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DPRINTF(Cache, "Replacing SCUpgradeReq with SCUpgradeFailReq\n");
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} else if (pkt->cmd == MemCmd::StoreCondReq) {
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pkt->cmd = MemCmd::StoreCondFailReq;
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DPRINTF(Cache, "Replacing StoreCondReq with StoreCondFailReq\n");
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}
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if (!has_data) {
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// there is no sensible way of setting the data field if the
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// new command actually would carry data
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assert(!pkt->hasData());
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if (pkt->hasRespData()) {
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// we went from a packet that had no data (neither request,
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// nor response), to one that does, and therefore we need to
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// actually allocate space for the data payload
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pkt->allocate();
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}
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}
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}
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void
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MSHR::TargetList::replaceUpgrades()
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{
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if (!hasUpgrade)
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return;
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for (auto& t : *this) {
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replaceUpgrade(t.pkt);
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}
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hasUpgrade = false;
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}
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void
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MSHR::TargetList::clearDownstreamPending()
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{
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for (auto& t : *this) {
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if (t.markedPending) {
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// Iterate over the SenderState stack and see if we find
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// an MSHR entry. If we find one, clear the
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// downstreamPending flag by calling
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// clearDownstreamPending(). This recursively clears the
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// downstreamPending flag in all caches this packet has
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// passed through.
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MSHR *mshr = t.pkt->findNextSenderState<MSHR>();
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if (mshr != nullptr) {
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mshr->clearDownstreamPending();
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}
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t.markedPending = false;
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}
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}
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}
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bool
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MSHR::TargetList::checkFunctional(PacketPtr pkt)
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{
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for (auto& t : *this) {
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if (pkt->checkFunctional(t.pkt)) {
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return true;
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}
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}
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return false;
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}
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void
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MSHR::TargetList::print(std::ostream &os, int verbosity,
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const std::string &prefix) const
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{
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for (auto& t : *this) {
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const char *s;
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switch (t.source) {
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case Target::FromCPU:
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s = "FromCPU";
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break;
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case Target::FromSnoop:
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s = "FromSnoop";
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break;
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case Target::FromPrefetcher:
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s = "FromPrefetcher";
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break;
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default:
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s = "";
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break;
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}
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ccprintf(os, "%s%s: ", prefix, s);
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t.pkt->print(os, verbosity, "");
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}
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}
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void
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MSHR::allocate(Addr blk_addr, unsigned blk_size, PacketPtr target,
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Tick when_ready, Counter _order, bool alloc_on_fill)
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{
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blkAddr = blk_addr;
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blkSize = blk_size;
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isSecure = target->isSecure();
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readyTime = when_ready;
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order = _order;
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assert(target);
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isForward = false;
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_isUncacheable = target->req->isUncacheable();
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inService = false;
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downstreamPending = false;
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assert(targets.isReset());
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// Don't know of a case where we would allocate a new MSHR for a
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// snoop (mem-side request), so set source according to request here
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Target::Source source = (target->cmd == MemCmd::HardPFReq) ?
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Target::FromPrefetcher : Target::FromCPU;
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targets.add(target, when_ready, _order, source, true, alloc_on_fill);
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assert(deferredTargets.isReset());
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}
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void
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MSHR::clearDownstreamPending()
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{
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assert(downstreamPending);
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downstreamPending = false;
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// recursively clear flag on any MSHRs we will be forwarding
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// responses to
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targets.clearDownstreamPending();
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}
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void
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MSHR::markInService(bool pending_modified_resp)
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{
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assert(!inService);
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inService = true;
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pendingModified = targets.needsWritable || pending_modified_resp;
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postInvalidate = postDowngrade = false;
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if (!downstreamPending) {
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// let upstream caches know that the request has made it to a
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// level where it's going to get a response
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targets.clearDownstreamPending();
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}
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}
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void
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MSHR::deallocate()
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{
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assert(targets.empty());
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targets.resetFlags();
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assert(deferredTargets.isReset());
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inService = false;
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}
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/*
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* Adds a target to an MSHR
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*/
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void
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MSHR::allocateTarget(PacketPtr pkt, Tick whenReady, Counter _order,
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bool alloc_on_fill)
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{
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// assume we'd never issue a prefetch when we've got an
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// outstanding miss
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assert(pkt->cmd != MemCmd::HardPFReq);
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// uncacheable accesses always allocate a new MSHR, and cacheable
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// accesses ignore any uncacheable MSHRs, thus we should never
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// have targets addded if originally allocated uncacheable
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assert(!_isUncacheable);
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// if there's a request already in service for this MSHR, we will
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// have to defer the new target until after the response if any of
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// the following are true:
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// - there are other targets already deferred
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// - there's a pending invalidate to be applied after the response
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// comes back (but before this target is processed)
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// - this target requires a writable block and either we're not
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// getting a writable block back or we have already snooped
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// another read request that will downgrade our writable block
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// to non-writable (Shared or Owned)
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if (inService &&
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(!deferredTargets.empty() || hasPostInvalidate() ||
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(pkt->needsWritable() &&
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(!isPendingModified() || hasPostDowngrade() || isForward)))) {
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// need to put on deferred list
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if (hasPostInvalidate())
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replaceUpgrade(pkt);
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deferredTargets.add(pkt, whenReady, _order, Target::FromCPU, true,
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alloc_on_fill);
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} else {
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// No request outstanding, or still OK to append to
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// outstanding request: append to regular target list. Only
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// mark pending if current request hasn't been issued yet
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// (isn't in service).
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targets.add(pkt, whenReady, _order, Target::FromCPU, !inService,
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alloc_on_fill);
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}
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}
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bool
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MSHR::handleSnoop(PacketPtr pkt, Counter _order)
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{
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DPRINTF(Cache, "%s for %s addr %#llx size %d\n", __func__,
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pkt->cmdString(), pkt->getAddr(), pkt->getSize());
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// when we snoop packets the needsWritable and isInvalidate flags
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// should always be the same, however, this assumes that we never
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// snoop writes as they are currently not marked as invalidations
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panic_if(pkt->needsWritable() != pkt->isInvalidate(),
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"%s got snoop %s to addr %#llx where needsWritable, "
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"does not match isInvalidate", name(), pkt->cmdString(),
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pkt->getAddr());
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if (!inService || (pkt->isExpressSnoop() && downstreamPending)) {
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// Request has not been issued yet, or it's been issued
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// locally but is buffered unissued at some downstream cache
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// which is forwarding us this snoop. Either way, the packet
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// we're snooping logically precedes this MSHR's request, so
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// the snoop has no impact on the MSHR, but must be processed
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// in the standard way by the cache. The only exception is
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// that if we're an L2+ cache buffering an UpgradeReq from a
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// higher-level cache, and the snoop is invalidating, then our
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// buffered upgrades must be converted to read exclusives,
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// since the upper-level cache no longer has a valid copy.
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// That is, even though the upper-level cache got out on its
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// local bus first, some other invalidating transaction
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// reached the global bus before the upgrade did.
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if (pkt->needsWritable()) {
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targets.replaceUpgrades();
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deferredTargets.replaceUpgrades();
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}
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return false;
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}
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// From here on down, the request issued by this MSHR logically
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// precedes the request we're snooping.
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if (pkt->needsWritable()) {
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// snooped request still precedes the re-request we'll have to
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// issue for deferred targets, if any...
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deferredTargets.replaceUpgrades();
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}
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if (hasPostInvalidate()) {
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// a prior snoop has already appended an invalidation, so
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// logically we don't have the block anymore; no need for
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// further snooping.
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return true;
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}
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if (isPendingModified() || pkt->isInvalidate()) {
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// We need to save and replay the packet in two cases:
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// 1. We're awaiting a writable copy (Modified or Exclusive),
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// so this MSHR is the orgering point, and we need to respond
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// after we receive data.
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// 2. It's an invalidation (e.g., UpgradeReq), and we need
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// to forward the snoop up the hierarchy after the current
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// transaction completes.
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// Start by determining if we will eventually respond or not,
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// matching the conditions checked in Cache::handleSnoop
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bool will_respond = isPendingModified() && pkt->needsResponse() &&
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pkt->cmd != MemCmd::InvalidateReq;
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// The packet we are snooping may be deleted by the time we
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// actually process the target, and we consequently need to
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// save a copy here. Clear flags and also allocate new data as
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// the original packet data storage may have been deleted by
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// the time we get to process this packet. In the cases where
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// we are not responding after handling the snoop we also need
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// to create a copy of the request to be on the safe side. In
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// the latter case the cache is responsible for deleting both
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// the packet and the request as part of handling the deferred
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// snoop.
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PacketPtr cp_pkt = will_respond ? new Packet(pkt, true, true) :
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new Packet(new Request(*pkt->req), pkt->cmd);
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if (will_respond) {
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// we are the ordering point, and will consequently
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// respond, and depending on whether the packet
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// needsWritable or not we either pass a Shared line or a
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// Modified line
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pkt->setCacheResponding();
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// inform the cache hierarchy that this cache had the line
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// in the Modified state, even if the response is passed
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// as Shared (and thus non-writable)
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pkt->setResponderHadWritable();
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// in the case of an uncacheable request there is no need
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// to set the responderHadWritable flag, but since the
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// recipient does not care there is no harm in doing so
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}
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targets.add(cp_pkt, curTick(), _order, Target::FromSnoop,
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downstreamPending && targets.needsWritable, false);
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if (pkt->needsWritable()) {
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// This transaction will take away our pending copy
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postInvalidate = true;
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}
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}
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if (!pkt->needsWritable() && !pkt->req->isUncacheable()) {
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// This transaction will get a read-shared copy, downgrading
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// our copy if we had a writable one
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postDowngrade = true;
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// make sure that any downstream cache does not respond with a
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// writable (and dirty) copy even if it has one, unless it was
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// explicitly asked for one
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pkt->setHasSharers();
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}
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return true;
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}
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MSHR::TargetList
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MSHR::extractServiceableTargets(PacketPtr pkt)
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{
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TargetList ready_targets;
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// If the downstream MSHR got an invalidation request then we only
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// service the first of the FromCPU targets and any other
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// non-FromCPU target. This way the remaining FromCPU targets
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// issue a new request and get a fresh copy of the block and we
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// avoid memory consistency violations.
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if (pkt->cmd == MemCmd::ReadRespWithInvalidate) {
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auto it = targets.begin();
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assert(it->source == Target::FromCPU);
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ready_targets.push_back(*it);
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it = targets.erase(it);
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while (it != targets.end()) {
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if (it->source == Target::FromCPU) {
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it++;
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} else {
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assert(it->source == Target::FromSnoop);
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ready_targets.push_back(*it);
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it = targets.erase(it);
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}
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}
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ready_targets.populateFlags();
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} else {
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std::swap(ready_targets, targets);
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}
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targets.populateFlags();
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return ready_targets;
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}
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bool
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MSHR::promoteDeferredTargets()
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{
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if (targets.empty()) {
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if (deferredTargets.empty()) {
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return false;
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}
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std::swap(targets, deferredTargets);
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} else {
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// If the targets list is not empty then we have one targets
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// from the deferredTargets list to the targets list. A new
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// request will then service the targets list.
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targets.splice(targets.end(), deferredTargets);
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targets.populateFlags();
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}
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// clear deferredTargets flags
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deferredTargets.resetFlags();
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order = targets.front().order;
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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();
|
|
}
|