1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
|
/*
* Copyright (c) 2019 Inria
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Daniel Carvalho
*/
/** @file
* Implementation of the a multi compressor that choses the best compression
* among multiple compressors.
*/
#include "mem/cache/compressors/multi.hh"
#include <cmath>
#include <queue>
#include "base/bitfield.hh"
#include "debug/CacheComp.hh"
#include "params/MultiCompressor.hh"
MultiCompressor::MultiCompData::MultiCompData(unsigned index,
std::unique_ptr<BaseCacheCompressor::CompressionData> comp_data)
: CompressionData(), index(index), compData(std::move(comp_data))
{
setSizeBits(compData->getSizeBits());
}
uint8_t
MultiCompressor::MultiCompData::getIndex() const
{
return index;
}
MultiCompressor::MultiCompressor(const Params *p)
: BaseCacheCompressor(p), compressors(p->compressors)
{
fatal_if(compressors.size() == 0, "There must be at least one compressor");
}
MultiCompressor::~MultiCompressor()
{
for (auto& compressor : compressors) {
delete compressor;
}
}
std::unique_ptr<BaseCacheCompressor::CompressionData>
MultiCompressor::compress(const uint64_t* cache_line, Cycles& comp_lat,
Cycles& decomp_lat)
{
struct Results
{
unsigned index;
std::unique_ptr<BaseCacheCompressor::CompressionData> compData;
Cycles decompLat;
uint8_t compressionFactor;
Results(unsigned index,
std::unique_ptr<BaseCacheCompressor::CompressionData> comp_data,
Cycles decomp_lat, std::size_t blk_size)
: index(index), compData(std::move(comp_data)),
decompLat(decomp_lat)
{
const std::size_t size = compData->getSize();
// If the compressed size is worse than the uncompressed size,
// we assume the size is the uncompressed size, and thus the
// compression factor is 1
compressionFactor = (size > blk_size) ? 1 :
alignToPowerOfTwo(std::floor(blk_size / (double) size));
}
};
struct ResultsComparator
{
bool
operator()(const std::shared_ptr<Results>& lhs,
const std::shared_ptr<Results>& rhs) const
{
const std::size_t lhs_cf = lhs->compressionFactor;
const std::size_t rhs_cf = rhs->compressionFactor;
if (lhs_cf == rhs_cf) {
// When they have similar compressed sizes, give the one
// with fastest decompression privilege
return lhs->decompLat < rhs->decompLat;
}
return lhs_cf < rhs_cf;
}
};
// Find the ranking of the compressor outputs
std::priority_queue<std::shared_ptr<Results>,
std::vector<std::shared_ptr<Results>>, ResultsComparator> results;
Cycles max_comp_lat;
for (unsigned i = 0; i < compressors.size(); i++) {
Cycles temp_decomp_lat;
auto temp_comp_data =
compressors[i]->compress(cache_line, comp_lat, temp_decomp_lat);
results.push(std::make_shared<Results>(i, std::move(temp_comp_data),
temp_decomp_lat, blkSize));
max_comp_lat = std::max(max_comp_lat, comp_lat);
}
// Assign best compressor to compression data
const unsigned best_index = results.top()->index;
std::unique_ptr<CompressionData> multi_comp_data =
std::unique_ptr<MultiCompData>(
new MultiCompData(best_index, std::move(results.top()->compData)));
DPRINTF(CacheComp, "Best compressor: %d\n", best_index);
// Set decompression latency of the best compressor
decomp_lat = results.top()->decompLat;
// Update compressor ranking stats
for (int rank = 0; rank < compressors.size(); rank++) {
rankStats[results.top()->index][rank]++;
results.pop();
}
// Set compression latency (compression latency of the slowest compressor
// and 1 cycle to pack)
comp_lat = Cycles(max_comp_lat + 1);
return multi_comp_data;
}
void
MultiCompressor::decompress(const CompressionData* comp_data,
uint64_t* cache_line)
{
const MultiCompData* casted_comp_data =
static_cast<const MultiCompData*>(comp_data);
compressors[casted_comp_data->getIndex()]->decompress(
casted_comp_data->compData.get(), cache_line);
}
void
MultiCompressor::regStats()
{
BaseCacheCompressor::regStats();
rankStats
.init(compressors.size(), compressors.size())
.name(name() + ".rank")
.desc("Number of times each compressor had the nth best compression.")
;
for (int compressor = 0; compressor < compressors.size(); compressor++) {
rankStats.subname(compressor, std::to_string(compressor));
rankStats.subdesc(compressor, "Number of times compressor " +
std::to_string(compressor) + " had the nth best compression.");
for (unsigned rank = 0; rank < compressors.size(); rank++) {
rankStats.ysubname(rank, std::to_string(rank));
}
}
}
MultiCompressor*
MultiCompressorParams::create()
{
return new MultiCompressor(this);
}
|
