src/mem/cache/mshr_queue.hh

   1 /*
   2  * Copyright (c) 2012-2013, 2015-2016, 2018 ARM Limited
   3  * All rights reserved.
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   5  * The license below extends only to copyright in the software and shall
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   8  * to a hardware implementation of the functionality of the software
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  11  * unmodified and in its entirety in all distributions of the software,
  12  * modified or unmodified, in source code or in binary form.
  13  *
  14  * Copyright (c) 2003-2005 The Regents of The University of Michigan
  15  * All rights reserved.
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  18  * modification, are permitted provided that the following conditions are
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  26  * this software without specific prior written permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  29  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  30  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  31  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  32  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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  34  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  35  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  36  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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  38  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  39  *
  40  * Authors: Erik Hallnor
  41  *          Andreas Sandberg
  42  */
  43
  44 /** @file
  45  * Declaration of a structure to manage MSHRs.
  46  */
  47
  48 #ifndef __MEM_CACHE_MSHR_QUEUE_HH__
  49 #define __MEM_CACHE_MSHR_QUEUE_HH__
  50
  51 #include <string>
  52
  53 #include "base/types.hh"
  54 #include "mem/cache/mshr.hh"
  55 #include "mem/cache/queue.hh"
  56 #include "mem/packet.hh"
  57
  58 /**
  59  * A Class for maintaining a list of pending and allocated memory requests.
  60  */
  61 class MSHRQueue : public Queue<MSHR>
  62 {
  63   private:
  64
  65     /**
  66      * The number of entries to reserve for future demand accesses.
  67      * Prevent prefetcher from taking all mshr entries
  68      */
  69     const int demandReserve;
  70
  71   public:
  72
  73     /**
  74      * Create a queue with a given number of entries.
  75      * @param num_entrys The number of entries in this queue.
  76      * @param reserve The minimum number of entries needed to satisfy
  77      * any access.
  78      * @param demand_reserve The minimum number of entries needed to satisfy
  79      * demand accesses.
  80      */
  81     MSHRQueue(const std::string &_label, int num_entries, int reserve,
  82               int demand_reserve);
  83
  84     /**
  85      * Allocates a new MSHR for the request and size. This places the request
  86      * as the first target in the MSHR.
  87      *
  88      * @param blk_addr The address of the block.
  89      * @param blk_size The number of bytes to request.
  90      * @param pkt The original miss.
  91      * @param when_ready When should the MSHR be ready to act upon.
  92      * @param order The logical order of this MSHR
  93      * @param alloc_on_fill Should the cache allocate a block on fill
  94      *
  95      * @return The a pointer to the MSHR allocated.
  96      *
  97      * @pre There are free entries.
  98      */
  99     MSHR *allocate(Addr blk_addr, unsigned blk_size, PacketPtr pkt,
 100                    Tick when_ready, Counter order, bool alloc_on_fill);
 101
 102     /**
 103      * Moves the MSHR to the front of the pending list if it is not
 104      * in service.
 105      * @param mshr The entry to move.
 106      */
 107     void moveToFront(MSHR *mshr);
 108
 109     /**
 110      * Adds a delay to the provided MSHR and moves MSHRs that will be
 111      * ready earlier than this entry to the top of the list
 112      *
 113      * @param mshr that needs to be delayed
 114      * @param delay_ticks ticks of the desired delay
 115      */
 116     void delay(MSHR *mshr, Tick delay_ticks);
 117
 118     /**
 119      * Mark the given MSHR as in service. This removes the MSHR from the
 120      * readyList or deallocates the MSHR if it does not expect a response.
 121      *
 122      * @param mshr The MSHR to mark in service.
 123      * @param pending_modified_resp Whether we expect a modified response
 124      *                              from another cache
 125      */
 126     void markInService(MSHR *mshr, bool pending_modified_resp);
 127
 128     /**
 129      * Mark an in service entry as pending, used to resend a request.
 130      * @param mshr The MSHR to resend.
 131      */
 132     void markPending(MSHR *mshr);
 133
 134     /**
 135      * Deallocate top target, possibly freeing the MSHR
 136      * @return if MSHR queue is no longer full
 137      */
 138     bool forceDeallocateTarget(MSHR *mshr);
 139
 140     /**
 141      * Returns true if the pending list is not empty.
 142      * @return True if there are outstanding requests.
 143      */
 144     bool havePending() const
 145     {
 146         return !readyList.empty();
 147     }
 148
 149     /**
 150      * Returns true if sufficient mshrs for prefetch.
 151      * @return True if sufficient mshrs for prefetch.
 152      */
 153     bool canPrefetch() const
 154     {
 155         // @todo we may want to revisit the +1, currently added to
 156         // keep regressions unchanged
 157         return (allocated < numEntries - (numReserve + 1 + demandReserve));
 158     }
 159 };
 160
 161 #endif //__MEM_CACHE_MSHR_QUEUE_HH__