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 "base/sat_counter.hh"
58#include "mem/cache/replacement_policies/base.hh"
59
60struct BRRIPRPParams;
61
62class BRRIPRP : public BaseReplacementPolicy
63{
64  protected:
65    /** BRRIP-specific implementation of replacement data. */
66    struct BRRIPReplData : ReplacementData
67    {
68        /**
69         * Re-Reference Interval Prediction Value.
70         * Some values have specific names (according to the paper):
71         * 0 -> near-immediate re-rereference interval
72         * max_RRPV-1 -> long re-rereference interval
73         * max_RRPV -> distant re-rereference interval
74         */
75        SatCounter rrpv;
76
77        /** Whether the entry is valid. */
78        bool valid;
79
80        /**
81         * Default constructor. Invalidate data.
82         */
83        BRRIPReplData(const int num_bits)
84            : rrpv(num_bits), valid(false)
85        {
86        }
87    };
88
89    /**
90     * Number of RRPV bits. An entry that saturates its RRPV has the longest
91     * possible re-reference interval, that is, it is likely not to be used
92     * in the near future, and is among the best eviction candidates.
93     * A maximum RRPV of 1 implies in a NRU.
94     */
95    const unsigned numRRPVBits;
96
97    /**
98     * The hit priority (HP) policy replaces entries that do not receive cache
99     * hits over any cache entry that receives a hit, while the frequency
100     * priority (FP) policy replaces infrequently re-referenced entries.
101     */
102    const bool hitPriority;
103
104    /**
105     * Bimodal throtle parameter. Value in the range [0,100] used to decide
106     * if a new entry is inserted with long or distant re-reference.
107     */
108    const unsigned btp;
109
110  public:
111    /** Convenience typedef. */
112    typedef BRRIPRPParams Params;
113
114    /**
115     * Construct and initiliaze this replacement policy.
116     */
117    BRRIPRP(const Params *p);
118
119    /**
120     * Destructor.
121     */
122    ~BRRIPRP() {}
123
124    /**
125     * Invalidate replacement data to set it as the next probable victim.
126     * Set RRPV as the the most distant re-reference.
127     *
128     * @param replacement_data Replacement data to be invalidated.
129     */
130    void invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
131                                                              const override;
132
133    /**
134     * Touch an entry to update its replacement data.
135     *
136     * @param replacement_data Replacement data to be touched.
137     */
138    void touch(const std::shared_ptr<ReplacementData>& replacement_data) const
139                                                                     override;
140
141    /**
142     * Reset replacement data. Used when an entry is inserted.
143     * Set RRPV according to the insertion policy used.
144     *
145     * @param replacement_data Replacement data to be reset.
146     */
147    void reset(const std::shared_ptr<ReplacementData>& replacement_data) const
148                                                                     override;
149
150    /**
151     * Find replacement victim using rrpv.
152     *
153     * @param cands Replacement candidates, selected by indexing policy.
154     * @return Replacement entry to be replaced.
155     */
156    ReplaceableEntry* getVictim(const ReplacementCandidates& candidates) const
157                                                                     override;
158
159    /**
160     * Instantiate a replacement data entry.
161     *
162     * @return A shared pointer to the new replacement data.
163     */
164    std::shared_ptr<ReplacementData> instantiateEntry() override;
165};
166
167#endif // __MEM_CACHE_REPLACEMENT_POLICIES_BRRIP_RP_HH__
168