brrip_rp.cc revision 12727:56c23b54bcb1 
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#include "mem/cache/replacement_policies/brrip_rp.hh"
32
33#include <cassert>
34#include <memory>
35
36#include "base/logging.hh" // For fatal_if
37#include "base/random.hh"
38#include "params/BRRIPRP.hh"
39
40BRRIPRP::BRRIPRP(const Params *p)
41    : BaseReplacementPolicy(p),
42      maxRRPV(p->max_RRPV), hitPriority(p->hit_priority), btp(p->btp)
43{
44    fatal_if(maxRRPV <= 0, "max_RRPV should be greater than zero.\n");
45}
46
47void
48BRRIPRP::invalidate(const std::shared_ptr<ReplacementData>& replacement_data)
49const
50{
51    std::shared_ptr<BRRIPReplData> casted_replacement_data =
52        std::static_pointer_cast<BRRIPReplData>(replacement_data);
53
54    // Set RRPV to an invalid distance
55    casted_replacement_data->rrpv = maxRRPV + 1;
56}
57
58void
59BRRIPRP::touch(const std::shared_ptr<ReplacementData>& replacement_data) const
60{
61    std::shared_ptr<BRRIPReplData> casted_replacement_data =
62        std::static_pointer_cast<BRRIPReplData>(replacement_data);
63
64    // Update RRPV if not 0 yet
65    // Every hit in HP mode makes the entry the last to be evicted, while
66    // in FP mode a hit makes the entry less likely to be evicted
67    if (hitPriority) {
68        casted_replacement_data->rrpv = 0;
69    } else if (casted_replacement_data->rrpv > 0) {
70        casted_replacement_data->rrpv--;
71    }
72}
73
74void
75BRRIPRP::reset(const std::shared_ptr<ReplacementData>& replacement_data) const
76{
77    std::shared_ptr<BRRIPReplData> casted_replacement_data =
78        std::static_pointer_cast<BRRIPReplData>(replacement_data);
79
80    // Reset RRPV
81    // Replacement data is inserted as "long re-reference" if lower than btp,
82    // "distant re-reference" otherwise
83    if (random_mt.random<unsigned>(1, 100) <= btp) {
84        casted_replacement_data->rrpv = maxRRPV-1;
85    } else {
86        casted_replacement_data->rrpv = maxRRPV;
87    }
88}
89
90ReplaceableEntry*
91BRRIPRP::getVictim(const ReplacementCandidates& candidates) const
92{
93    // There must be at least one replacement candidate
94    assert(candidates.size() > 0);
95
96    // Use first candidate as dummy victim
97    ReplaceableEntry* victim = candidates[0];
98
99    // Store victim->rrpv in a variable to improve code readability
100    int victim_RRPV = std::static_pointer_cast<BRRIPReplData>(
101                        victim->replacementData)->rrpv;
102
103    // Visit all candidates to find victim
104    for (const auto& candidate : candidates) {
105        // Get candidate's rrpv
106        int candidate_RRPV = std::static_pointer_cast<BRRIPReplData>(
107                                    candidate->replacementData)->rrpv;
108
109        // Stop searching for victims if an invalid entry is found
110        if (candidate_RRPV == maxRRPV + 1) {
111            return candidate;
112        // Update victim entry if necessary
113        } else if (candidate_RRPV > victim_RRPV) {
114            victim = candidate;
115            victim_RRPV = candidate_RRPV;
116        }
117    }
118
119    // Get difference of victim's RRPV to the highest possible RRPV in
120    // order to update the RRPV of all the other entries accordingly
121    int diff = maxRRPV - victim_RRPV;
122
123    // No need to update RRPV if there is no difference
124    if (diff > 0){
125        // Update RRPV of all candidates
126        for (const auto& candidate : candidates) {
127            std::static_pointer_cast<BRRIPReplData>(
128                candidate->replacementData)->rrpv += diff;
129        }
130    }
131
132    return victim;
133}
134
135std::shared_ptr<ReplacementData>
136BRRIPRP::instantiateEntry()
137{
138    return std::shared_ptr<ReplacementData>(new BRRIPReplData(maxRRPV));
139}
140
141BRRIPRP*
142BRRIPRPParams::create()
143{
144    return new BRRIPRP(this);
145}
146