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      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}
152