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 Least Frequently Used replacement policy.
34 * The victim is chosen using the reference frequency. The least referenced
35 * entry is always chosen to be evicted, regardless of the amount of times
36 * it has been touched, or how long has passed since its last touch.
37 */
38
39#ifndef __MEM_CACHE_REPLACEMENT_POLICIES_LFU_RP_HH__
40#define __MEM_CACHE_REPLACEMENT_POLICIES_LFU_RP_HH__
41
42#include "mem/cache/replacement_policies/base.hh"
43
44struct LFURPParams;
45
46class LFURP : public BaseReplacementPolicy
47{
48  protected:
49    /** LFU-specific implementation of replacement data. */
50    struct LFUReplData : ReplacementData
51    {
52        /** Number of references to this entry since it was reset. */
53        unsigned refCount;
54
55        /**
56         * Default constructor. Invalidate data.
57         */
58        LFUReplData() : refCount(0) {}
59    };
60
61  public:
62    /** Convenience typedef. */
63    typedef LFURPParams Params;
64
65    /**
66     * Construct and initiliaze this replacement policy.
67     */
68    LFURP(const Params *p);
69
70    /**
71     * Destructor.
72     */
73    ~LFURP() {}
74
75    /**
76     * Invalidate replacement data to set it as the next probable victim.
77     * Clear the number of references.
78     *
79     * @param replacement_data Replacement data to be invalidated.
80     */
81    void invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
82                                                              const override;
83
84    /**
85     * Touch an entry to update its replacement data.
86     * Increase number of references.
87     *
88     * @param replacement_data Replacement data to be touched.
89     */
90    void touch(const std::shared_ptr<ReplacementData>& replacement_data) const
91                                                                     override;
92
93    /**
94     * Reset replacement data. Used when an entry is inserted.
95     * Reset number of references.
96     *
97     * @param replacement_data Replacement data to be reset.
98     */
99    void reset(const std::shared_ptr<ReplacementData>& replacement_data) const
100                                                                     override;
101
102    /**
103     * Find replacement victim using reference frequency.
104     *
105     * @param cands Replacement candidates, selected by indexing policy.
106     * @return Replacement entry to be replaced.
107     */
108    ReplaceableEntry* getVictim(const ReplacementCandidates& candidates) const
109                                                                     override;
110
111    /**
112     * Instantiate a replacement data entry.
113     *
114     * @return A shared pointer to the new replacement data.
115     */
116    std::shared_ptr<ReplacementData> instantiateEntry() override;
117};
118
119#endif // __MEM_CACHE_REPLACEMENT_POLICIES_LFU_RP_HH__
120