brrip_rp.hh revision 13849 
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
59struct BRRIPRPParams;
60
61class BRRIPRP : public BaseReplacementPolicy
62{
63  protected:
64    /** BRRIP-specific implementation of replacement data. */
65    struct BRRIPReplData : ReplacementData
66    {
67        /**
68         * Re-Reference Interval Prediction Value.
69         * Some values have specific names (according to the paper):
70         * 0 -> near-immediate re-rereference interval
71         * max_RRPV-1 -> long re-rereference interval
72         * max_RRPV -> distant re-rereference interval
73         * A value equal to max_RRPV + 1 indicates an invalid entry.
74         */
75        int rrpv;
76
77        /**
78         * Default constructor. Invalidate data.
79         */
80        BRRIPReplData(const int max_RRPV) : rrpv(max_RRPV + 1) {}
81    };
82
83    /**
84     * Maximum Re-Reference Prediction Value possible. An entry with this
85     * value as the rrpv has the longest possible re-reference interval,
86     * that is, it is likely not to be used in the near future, and is
87     * among the best eviction candidates.
88     * A maxRRPV of 1 implies in a NRU.
89     */
90    const int maxRRPV;
91
92    /**
93     * The hit priority (HP) policy replaces entries that do not receive cache
94     * hits over any cache entry that receives a hit, while the frequency
95     * priority (FP) policy replaces infrequently re-referenced entries.
96     */
97    const bool hitPriority;
98
99    /**
100     * Bimodal throtle parameter. Value in the range [0,100] used to decide
101     * if a new entry is inserted with long or distant re-reference.
102     */
103    const unsigned btp;
104
105  public:
106    /** Convenience typedef. */
107    typedef BRRIPRPParams Params;
108
109    /**
110     * Construct and initiliaze this replacement policy.
111     */
112    BRRIPRP(const Params *p);
113
114    /**
115     * Destructor.
116     */
117    ~BRRIPRP() {}
118
119    /**
120     * Invalidate replacement data to set it as the next probable victim.
121     * Set RRPV as the the most distant re-reference.
122     *
123     * @param replacement_data Replacement data to be invalidated.
124     */
125    void invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
126                                                              const override;
127
128    /**
129     * Touch an entry to update its replacement data.
130     *
131     * @param replacement_data Replacement data to be touched.
132     */
133    void touch(const std::shared_ptr<ReplacementData>& replacement_data) const
134                                                                     override;
135
136    /**
137     * Reset replacement data. Used when an entry is inserted.
138     * Set RRPV according to the insertion policy used.
139     *
140     * @param replacement_data Replacement data to be reset.
141     */
142    void reset(const std::shared_ptr<ReplacementData>& replacement_data) const
143                                                                     override;
144
145    /**
146     * Find replacement victim using rrpv.
147     *
148     * @param cands Replacement candidates, selected by indexing policy.
149     * @return Replacement entry to be replaced.
150     */
151    ReplaceableEntry* getVictim(const ReplacementCandidates& candidates) const
152                                                                     override;
153
154    /**
155     * Instantiate a replacement data entry.
156     *
157     * @return A shared pointer to the new replacement data.
158     */
159    std::shared_ptr<ReplacementData> instantiateEntry() override;
160};
161
162#endif // __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
163