src/mem/cache/replacement_policies/brrip_rp.hh

   1 /**
   2  * Copyright (c) 2018 Inria
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  *
  28  * Authors: Daniel Carvalho
  29  */
  30
  31 /**
  32  * @file
  33  * Declaration of a Re-Reference Interval Prediction replacement policy.
  34  *
  35  * Not-Recently Used (NRU) is an approximation of LRU that uses a single bit
  36  * to determine if an entry is going to be re-referenced in the near or distant
  37  * future.
  38  *
  39  * Re-Reference Interval Prediction (RRIP) is an extension of NRU that uses a
  40  * re-reference prediction value to determine if entries are going to be re-
  41  * used in the near future or not.
  42  *
  43  * The higher the value of the RRPV, the more distant the entry is from its
  44  * next access.
  45  *
  46  * Bimodal Re-Reference Interval Prediction (BRRIP) is an extension of RRIP
  47  * that has a probability of not inserting entries as the LRU. This probability
  48  * is controlled by the bimodal throtle parameter (btp).
  49  *
  50  * From the original paper, this implementation of RRIP is also called
  51  * Static RRIP (SRRIP), as it always inserts entries with the same RRPV.
  52  */
  53
  54 #ifndef __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
  55 #define __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
  56
  57 #include "mem/cache/replacement_policies/base.hh"
  58 #include "params/BRRIPRP.hh"
  59
  60 class BRRIPRP : public BaseReplacementPolicy
  61 {
  62   protected:
  63     /** BRRIP-specific implementation of replacement data. */
  64     struct BRRIPReplData : ReplacementData
  65     {
  66         /**
  67          * Re-Reference Interval Prediction Value.
  68          * A value equal to max_RRPV + 1 indicates an invalid entry.
  69          */
  70         int rrpv;
  71
  72         /**
  73          * Default constructor. Invalidate data.
  74          */
  75         BRRIPReplData(const int max_RRPV) : rrpv(max_RRPV + 1) {}
  76     };
  77
  78     /**
  79      * Maximum Re-Reference Prediction Value possible. An entry with this
  80      * value as the rrpv has the longest possible re-reference interval,
  81      * that is, it is likely not to be used in the near future, and is
  82      * among the best eviction candidates.
  83      * A maxRRPV of 1 implies in a NRU.
  84      */
  85     const int maxRRPV;
  86
  87     /**
  88      * The hit priority (HP) policy replaces entries that do not receive cache
  89      * hits over any cache entry that receives a hit, while the frequency
  90      * priority (FP) policy replaces infrequently re-referenced entries.
  91      */
  92     const bool hitPriority;
  93
  94     /**
  95      * Bimodal throtle parameter. Value in the range [0,100] used to decide
  96      * if a new entry is inserted with long or distant re-reference.
  97      */
  98     const unsigned btp;
  99
 100   public:
 101     /** Convenience typedef. */
 102     typedef BRRIPRPParams Params;
 103
 104     /**
 105      * Construct and initiliaze this replacement policy.
 106      */
 107     BRRIPRP(const Params *p);
 108
 109     /**
 110      * Destructor.
 111      */
 112     ~BRRIPRP() {}
 113
 114     /**
 115      * Invalidate replacement data to set it as the next probable victim.
 116      * Set RRPV as the the most distant re-reference.
 117      *
 118      * @param replacement_data Replacement data to be invalidated.
 119      */
 120     void invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
 121                                                               const override;
 122
 123     /**
 124      * Touch an entry to update its replacement data.
 125      *
 126      * @param replacement_data Replacement data to be touched.
 127      */
 128     void touch(const std::shared_ptr<ReplacementData>& replacement_data) const
 129                                                                      override;
 130
 131     /**
 132      * Reset replacement data. Used when an entry is inserted.
 133      * Set RRPV according to the insertion policy used.
 134      *
 135      * @param replacement_data Replacement data to be reset.
 136      */
 137     void reset(const std::shared_ptr<ReplacementData>& replacement_data) const
 138                                                                      override;
 139
 140     /**
 141      * Find replacement victim using rrpv.
 142      *
 143      * @param cands Replacement candidates, selected by indexing policy.
 144      * @return Replacement entry to be replaced.
 145      */
 146     ReplaceableEntry* getVictim(const ReplacementCandidates& candidates) const
 147                                                                      override;
 148
 149     /**
 150      * Instantiate a replacement data entry.
 151      *
 152      * @return A shared pointer to the new replacement data.
 153      */
 154     std::shared_ptr<ReplacementData> instantiateEntry() override;
 155 };
 156
 157 #endif // __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__