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>
375 lines
13 KiB
C++
375 lines
13 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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* 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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*/
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/**
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* @file
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* Miss Status and Handling Register (MSHR) declaration.
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*/
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#ifndef __MEM_CACHE_MSHR_HH__
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#define __MEM_CACHE_MSHR_HH__
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#include <list>
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#include "base/printable.hh"
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#include "mem/cache/queue_entry.hh"
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class Cache;
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/**
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* Miss Status and handling Register. This class keeps all the information
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* needed to handle a cache miss including a list of target requests.
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* @sa \ref gem5MemorySystem "gem5 Memory System"
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*/
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class MSHR : public QueueEntry, public Printable
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{
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/**
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* Consider the queues friends to avoid making everything public.
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*/
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template<typename Entry>
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friend class Queue;
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friend class MSHRQueue;
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private:
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/** Flag set by downstream caches */
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bool downstreamPending;
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/**
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* Here we use one flag to track both if:
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*
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* 1. We are going to become owner or not, i.e., we will get the
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* block in an ownership state (Owned or Modified) with BlkDirty
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* set. This determines whether or not we are going to become the
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* responder and ordering point for future requests that we snoop.
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*
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* 2. We know that we are going to get a writable block, i.e. we
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* will get the block in writable state (Exclusive or Modified
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* state) with BlkWritable set. That determines whether additional
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* targets with needsWritable set will be able to be satisfied, or
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* if not should be put on the deferred list to possibly wait for
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* another request that does give us writable access.
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*
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* Condition 2 is actually just a shortcut that saves us from
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* possibly building a deferred target list and calling
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* promoteWritable() every time we get a writable block. Condition
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* 1, tracking ownership, is what is important. However, we never
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* receive ownership without marking the block dirty, and
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* consequently use pendingModified to track both ownership and
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* writability rather than having separate pendingDirty and
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* pendingWritable flags.
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*/
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bool pendingModified;
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/** Did we snoop an invalidate while waiting for data? */
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bool postInvalidate;
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/** Did we snoop a read while waiting for data? */
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bool postDowngrade;
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public:
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/** True if the entry is just a simple forward from an upper level */
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bool isForward;
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class Target {
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public:
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enum Source {
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FromCPU,
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FromSnoop,
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FromPrefetcher
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};
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const Tick recvTime; //!< Time when request was received (for stats)
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const Tick readyTime; //!< Time when request is ready to be serviced
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const Counter order; //!< Global order (for memory consistency mgmt)
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const PacketPtr pkt; //!< Pending request packet.
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const Source source; //!< Request from cpu, memory, or prefetcher?
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/**
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* We use this flag to track whether we have cleared the
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* downstreamPending flag for the MSHR of the cache above
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* where this packet originates from and guard noninitial
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* attempts to clear it.
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*
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* The flag markedPending needs to be updated when the
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* TargetList is in service which can be:
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* 1) during the Target instantiation if the MSHR is in
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* service and the target is not deferred,
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* 2) when the MSHR becomes in service if the target is not
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* deferred,
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* 3) or when the TargetList is promoted (deferredTargets ->
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* targets).
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*/
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bool markedPending;
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const bool allocOnFill; //!< Should the response servicing this
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//!< target list allocate in the cache?
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Target(PacketPtr _pkt, Tick _readyTime, Counter _order,
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Source _source, bool _markedPending, bool alloc_on_fill)
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: recvTime(curTick()), readyTime(_readyTime), order(_order),
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pkt(_pkt), source(_source), markedPending(_markedPending),
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allocOnFill(alloc_on_fill)
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{}
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};
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class TargetList : public std::list<Target> {
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public:
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bool needsWritable;
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bool hasUpgrade;
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/** Set when the response should allocate on fill */
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bool allocOnFill;
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TargetList();
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/**
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* Use the provided packet and the source to update the
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* flags of this TargetList.
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*
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* @param pkt Packet considered for the flag update
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* @param source Indicates the source of the packet
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* @param alloc_on_fill Whether the pkt would allocate on a fill
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*/
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void updateFlags(PacketPtr pkt, Target::Source source,
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bool alloc_on_fill);
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void resetFlags() { needsWritable = hasUpgrade = allocOnFill = false; }
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/**
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* Goes through the list of targets and uses them to populate
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* the flags of this TargetList. When the function returns the
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* flags are consistent with the properties of packets in the
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* list.
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*/
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void populateFlags();
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/**
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* Tests if the flags of this TargetList have their default
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* values.
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*/
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bool isReset() const {
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return !needsWritable && !hasUpgrade && !allocOnFill;
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}
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/**
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* Add the specified packet in the TargetList. This function
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* stores information related to the added packet and updates
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* accordingly the flags.
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*
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* @param pkt Packet considered for adding
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* @param readTime Tick at which the packet is processed by this cache
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* @param order A counter giving a unique id to each target
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* @param source Indicates the source agent of the packet
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* @param markPending Set for deferred targets or pending MSHRs
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* @param alloc_on_fill Whether it should allocate on a fill
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*/
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void add(PacketPtr pkt, Tick readyTime, Counter order,
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Target::Source source, bool markPending,
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bool alloc_on_fill);
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/**
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* Convert upgrades to the equivalent request if the cache line they
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* refer to would have been invalid (Upgrade -> ReadEx, SC* -> Fail).
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* Used to rejig ordering between targets waiting on an MSHR. */
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void replaceUpgrades();
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void clearDownstreamPending();
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bool checkFunctional(PacketPtr pkt);
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void print(std::ostream &os, int verbosity,
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const std::string &prefix) const;
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};
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/** A list of MSHRs. */
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typedef std::list<MSHR *> List;
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/** MSHR list iterator. */
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typedef List::iterator Iterator;
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/** The pending* and post* flags are only valid if inService is
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* true. Using the accessor functions lets us detect if these
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* flags are accessed improperly.
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*/
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/** True if we need to get a writable copy of the block. */
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bool needsWritable() const { return targets.needsWritable; }
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bool isPendingModified() const {
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assert(inService); return pendingModified;
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}
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bool hasPostInvalidate() const {
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assert(inService); return postInvalidate;
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}
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bool hasPostDowngrade() const {
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assert(inService); return postDowngrade;
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}
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bool sendPacket(Cache &cache);
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bool allocOnFill() const {
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return targets.allocOnFill;
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}
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private:
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/**
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* Pointer to this MSHR on the ready list.
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* @sa MissQueue, MSHRQueue::readyList
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*/
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Iterator readyIter;
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/**
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* Pointer to this MSHR on the allocated list.
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* @sa MissQueue, MSHRQueue::allocatedList
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*/
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Iterator allocIter;
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/** List of all requests that match the address */
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TargetList targets;
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TargetList deferredTargets;
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public:
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/**
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* Allocate a miss to this MSHR.
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* @param blk_addr The address of the block.
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* @param blk_size The number of bytes to request.
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* @param pkt The original miss.
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* @param when_ready When should the MSHR be ready to act upon.
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* @param _order The logical order of this MSHR
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* @param alloc_on_fill Should the cache allocate a block on fill
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*/
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void allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
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Tick when_ready, Counter _order, bool alloc_on_fill);
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void markInService(bool pending_modified_resp);
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void clearDownstreamPending();
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/**
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* Mark this MSHR as free.
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*/
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void deallocate();
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/**
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* Add a request to the list of targets.
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* @param target The target.
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*/
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void allocateTarget(PacketPtr target, Tick when, Counter order,
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bool alloc_on_fill);
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bool handleSnoop(PacketPtr target, Counter order);
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/** A simple constructor. */
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MSHR();
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/**
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* Returns the current number of allocated targets.
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* @return The current number of allocated targets.
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*/
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int getNumTargets() const
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{ return targets.size() + deferredTargets.size(); }
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/**
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* Extracts the subset of the targets that can be serviced given a
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* received response. This function returns the targets list
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* unless the response is a ReadRespWithInvalidate. The
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* ReadRespWithInvalidate is only invalidating response that its
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* invalidation was not expected when the request (a
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* ReadSharedReq) was sent out. For ReadRespWithInvalidate we can
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* safely service only the first FromCPU target and all FromSnoop
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* targets (inform all snoopers that we no longer have the block).
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*
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* @param pkt The response from the downstream memory
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*/
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TargetList extractServiceableTargets(PacketPtr pkt);
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/**
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* Returns true if there are targets left.
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* @return true if there are targets
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*/
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bool hasTargets() const { return !targets.empty(); }
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/**
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* Returns a reference to the first target.
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* @return A pointer to the first target.
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*/
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Target *getTarget()
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{
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assert(hasTargets());
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return &targets.front();
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}
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/**
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* Pop first target.
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*/
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void popTarget()
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{
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targets.pop_front();
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}
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bool promoteDeferredTargets();
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void promoteWritable();
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bool checkFunctional(PacketPtr pkt);
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/**
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* Prints the contents of this MSHR for debugging.
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*/
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void print(std::ostream &os,
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int verbosity = 0,
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const std::string &prefix = "") const;
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/**
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* A no-args wrapper of print(std::ostream...) meant to be
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* invoked from DPRINTFs avoiding string overheads in fast mode
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*
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* @return string with mshr fields + [deferred]targets
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*/
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std::string print() const;
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};
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#endif // __MEM_CACHE_MSHR_HH__
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