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;

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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 numRRPVBits(p->num_bits), hitPriority(p->hit_priority), btp(p->btp)
43{
44 fatal_if(numRRPVBits <= 0, "There should be at least one bit per RRPV.\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 // Invalidate entry
55 casted_replacement_data->valid = false;
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.reset();
69 } else {
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 casted_replacement_data->rrpv.saturate();
84 if (random_mt.random<unsigned>(1, 100) <= btp) {
85 casted_replacement_data->rrpv--;
86 }
87
88 // Mark entry as ready to be used
89 casted_replacement_data->valid = true;
90}
91
92ReplaceableEntry*
93BRRIPRP::getVictim(const ReplacementCandidates& candidates) const
94{
95 // There must be at least one replacement candidate
96 assert(candidates.size() > 0);
97
98 // Use first candidate as dummy victim
99 ReplaceableEntry* victim = candidates[0];
100
101 // Store victim->rrpv in a variable to improve code readability
102 int victim_RRPV = std::static_pointer_cast<BRRIPReplData>(
103 victim->replacementData)->rrpv;
104
105 // Visit all candidates to find victim
106 for (const auto& candidate : candidates) {
107 std::shared_ptr<BRRIPReplData> candidate_repl_data =
108 std::static_pointer_cast<BRRIPReplData>(
109 candidate->replacementData);
110
111 // Stop searching for victims if an invalid entry is found
112 if (!candidate_repl_data->valid) {
113 return candidate;
114 }
115
116 // Update victim entry if necessary
117 int candidate_RRPV = candidate_repl_data->rrpv;
118 if (candidate_RRPV > victim_RRPV) {
119 victim = candidate;
120 victim_RRPV = candidate_RRPV;
121 }
122 }
123
124 // Get difference of victim's RRPV to the highest possible RRPV in
125 // order to update the RRPV of all the other entries accordingly
126 int diff = std::static_pointer_cast<BRRIPReplData>(
127 victim->replacementData)->rrpv.saturate();
128
129 // No need to update RRPV if there is no difference
130 if (diff > 0){
131 // Update RRPV of all candidates
132 for (const auto& candidate : candidates) {
133 std::static_pointer_cast<BRRIPReplData>(
134 candidate->replacementData)->rrpv += diff;
135 }
136 }
137
138 return victim;
139}
140
141std::shared_ptr<ReplacementData>
142BRRIPRP::instantiateEntry()
143{
144 return std::shared_ptr<ReplacementData>(new BRRIPReplData(numRRPVBits));
145}
146
147BRRIPRP*
148BRRIPRPParams::create()
149{
150 return new BRRIPRP(this);
151}