base.cc revision 13945 
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/** @file
32 * Definition of a basic cache compressor.
33 */
34
35#include "mem/cache/compressors/base.hh"
36
37#include <algorithm>
38#include <cstdint>
39#include <string>
40
41#include "debug/CacheComp.hh"
42#include "mem/cache/tags/super_blk.hh"
43#include "params/BaseCacheCompressor.hh"
44
45// Uncomment this line if debugging compression
46//#define DEBUG_COMPRESSION
47
48BaseCacheCompressor::CompressionData::CompressionData()
49    : _size(0)
50{
51}
52
53BaseCacheCompressor::CompressionData::~CompressionData()
54{
55}
56
57void
58BaseCacheCompressor::CompressionData::setSizeBits(std::size_t size)
59{
60    _size = size;
61}
62
63std::size_t
64BaseCacheCompressor::CompressionData::getSizeBits() const
65{
66    return _size;
67}
68
69std::size_t
70BaseCacheCompressor::CompressionData::getSize() const
71{
72    return std::ceil(_size/8);
73}
74
75BaseCacheCompressor::BaseCacheCompressor(const Params *p)
76    : SimObject(p), blkSize(p->block_size)
77{
78}
79
80void
81BaseCacheCompressor::compress(const uint64_t* data, Cycles& comp_lat,
82                              Cycles& decomp_lat, std::size_t& comp_size_bits)
83{
84    // Apply compression
85    std::unique_ptr<CompressionData> comp_data =
86        compress(data, comp_lat, decomp_lat);
87
88    // If we are in debug mode apply decompression just after the compression.
89    // If the results do not match, we've got an error
90    #ifdef DEBUG_COMPRESSION
91    uint64_t decomp_data[blkSize/8];
92
93    // Apply decompression
94    decompress(comp_data.get(), decomp_data);
95
96    // Check if decompressed line matches original cache line
97    fatal_if(std::memcmp(data, decomp_data, blkSize),
98             "Decompressed line does not match original line.");
99    #endif
100
101    // Get compression size
102    comp_size_bits = comp_data->getSizeBits();
103
104    // Update stats
105    compressionSize[std::ceil(std::log2(comp_size_bits))]++;
106
107    // Print debug information
108    DPRINTF(CacheComp, "Compressed cache line from %d to %d bits. " \
109            "Compression latency: %llu, decompression latency: %llu\n",
110            blkSize*8, comp_size_bits, comp_lat, decomp_lat);
111}
112
113Cycles
114BaseCacheCompressor::getDecompressionLatency(const CacheBlk* blk) const
115{
116    const CompressionBlk* comp_blk = static_cast<const CompressionBlk*>(blk);
117
118    // If block is compressed, return its decompression latency
119    if (comp_blk && comp_blk->isCompressed()){
120        const Cycles decomp_lat = comp_blk->getDecompressionLatency();
121        DPRINTF(CacheComp, "Decompressing block: %s (%d cycles)\n",
122                comp_blk->print(), decomp_lat);
123        return decomp_lat;
124    }
125
126    // Block is not compressed, so there is no decompression latency
127    return Cycles(0);
128}
129
130void
131BaseCacheCompressor::setDecompressionLatency(CacheBlk* blk, const Cycles lat)
132{
133    // Sanity check
134    assert(blk != nullptr);
135
136    // Assign latency
137    static_cast<CompressionBlk*>(blk)->setDecompressionLatency(lat);
138}
139
140void
141BaseCacheCompressor::setSizeBits(CacheBlk* blk, const std::size_t size_bits)
142{
143    // Sanity check
144    assert(blk != nullptr);
145
146    // Assign size
147    static_cast<CompressionBlk*>(blk)->setSizeBits(size_bits);
148}
149
150void
151BaseCacheCompressor::regStats()
152{
153    SimObject::regStats();
154
155    // We also store when compression is bigger than original block size
156    compressionSize
157        .init(std::log2(blkSize*8) + 2)
158        .name(name() + ".compression_size")
159        .desc("Number of blocks that were compressed to this power of" \
160              "two size.")
161        ;
162
163    for (unsigned i = 0; i <= std::log2(blkSize*8) + 1; ++i) {
164        compressionSize.subname(i, std::to_string(1 << i));
165        compressionSize.subdesc(i, "Number of blocks that compressed to fit " \
166                                   "in " + std::to_string(1 << i) + " bits");
167    }
168}
169
170