src/mem/cache/compressors/base.cc

   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
  40 #include "debug/CacheComp.hh"
  41 #include "mem/cache/tags/super_blk.hh"
  42 #include "params/BaseCacheCompressor.hh"
  43
  44 // Uncomment this line if debugging compression
  45 //#define DEBUG_COMPRESSION
  46
  47 BaseCacheCompressor::CompressionData::CompressionData()
  48     : _size(0)
  49 {
  50 }
  51
  52 BaseCacheCompressor::CompressionData::~CompressionData()
  53 {
  54 }
  55
  56 void
  57 BaseCacheCompressor::CompressionData::setSizeBits(std::size_t size)
  58 {
  59     _size = size;
  60 }
  61
  62 std::size_t
  63 BaseCacheCompressor::CompressionData::getSizeBits() const
  64 {
  65     return _size;
  66 }
  67
  68 std::size_t
  69 BaseCacheCompressor::CompressionData::getSize() const
  70 {
  71     return std::ceil(_size/8);
  72 }
  73
  74 BaseCacheCompressor::BaseCacheCompressor(const Params *p)
  75     : SimObject(p), blkSize(p->block_size)
  76 {
  77 }
  78
  79 void
  80 BaseCacheCompressor::compress(const uint64_t* data, Cycles& comp_lat,
  81                               Cycles& decomp_lat, std::size_t& comp_size_bits)
  82 {
  83     // Apply compression
  84     std::unique_ptr<CompressionData> comp_data =
  85         compress(data, comp_lat, decomp_lat);
  86
  87     // If we are in debug mode apply decompression just after the compression.
  88     // If the results do not match, we've got an error
  89     #ifdef DEBUG_COMPRESSION
  90     uint64_t decomp_data[blkSize/8];
  91
  92     // Apply decompression
  93     decompress(comp_data.get(), decomp_data);
  94
  95     // Check if decompressed line matches original cache line
  96     fatal_if(std::memcmp(data, decomp_data, blkSize),
  97              "Decompressed line does not match original line.");
  98     #endif
  99
 100     // Get compression size
 101     comp_size_bits = comp_data->getSizeBits();
 102
 103     // Print debug information
 104     DPRINTF(CacheComp, "Compressed cache line from %d to %d bits. " \
 105             "Compression latency: %llu, decompression latency: %llu\n",
 106             blkSize*8, comp_size_bits, comp_lat, decomp_lat);
 107 }
 108
 109 Cycles
 110 BaseCacheCompressor::getDecompressionLatency(const CacheBlk* blk)
 111 {
 112     const CompressionBlk* comp_blk = static_cast<const CompressionBlk*>(blk);
 113
 114     // If block is compressed, return its decompression latency
 115     if (comp_blk && comp_blk->isCompressed()){
 116         return comp_blk->getDecompressionLatency();
 117     }
 118
 119     // Block is not compressed, so there is no decompression latency
 120     return Cycles(0);
 121 }
 122
 123 void
 124 BaseCacheCompressor::setDecompressionLatency(CacheBlk* blk, const Cycles lat)
 125 {
 126     // Sanity check
 127     assert(blk != nullptr);
 128
 129     // Assign latency
 130     static_cast<CompressionBlk*>(blk)->setDecompressionLatency(lat);
 131 }
 132
 133 void
 134 BaseCacheCompressor::setSizeBits(CacheBlk* blk, const std::size_t size_bits)
 135 {
 136     // Sanity check
 137     assert(blk != nullptr);
 138
 139     // Assign size
 140     static_cast<CompressionBlk*>(blk)->setSizeBits(size_bits);
 141 }
 142