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/*
* Copyright (c) 2018 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
* Definition of a basic cache compressor.
*/
#include "mem/cache/compressors/base.hh"
#include <algorithm>
#include <cstdint>
#include <string>
#include "debug/CacheComp.hh"
#include "mem/cache/tags/super_blk.hh"
#include "params/BaseCacheCompressor.hh"
// Uncomment this line if debugging compression
//#define DEBUG_COMPRESSION
BaseCacheCompressor::CompressionData::CompressionData()
: _size(0)
{
}
BaseCacheCompressor::CompressionData::~CompressionData()
{
}
void
BaseCacheCompressor::CompressionData::setSizeBits(std::size_t size)
{
_size = size;
}
std::size_t
BaseCacheCompressor::CompressionData::getSizeBits() const
{
return _size;
}
std::size_t
BaseCacheCompressor::CompressionData::getSize() const
{
return std::ceil(_size/8);
}
BaseCacheCompressor::BaseCacheCompressor(const Params *p)
: SimObject(p), blkSize(p->block_size), sizeThreshold(p->size_threshold)
{
fatal_if(blkSize < sizeThreshold, "Compressed data must fit in a block");
}
void
BaseCacheCompressor::compress(const uint64_t* data, Cycles& comp_lat,
Cycles& decomp_lat, std::size_t& comp_size_bits)
{
// Apply compression
std::unique_ptr<CompressionData> comp_data =
compress(data, comp_lat, decomp_lat);
// If we are in debug mode apply decompression just after the compression.
// If the results do not match, we've got an error
#ifdef DEBUG_COMPRESSION
uint64_t decomp_data[blkSize/8];
// Apply decompression
decompress(comp_data.get(), decomp_data);
// Check if decompressed line matches original cache line
fatal_if(std::memcmp(data, decomp_data, blkSize),
"Decompressed line does not match original line.");
#endif
// Get compression size. If compressed size is greater than the size
// threshold, the compression is seen as unsuccessful
comp_size_bits = comp_data->getSizeBits();
if (comp_size_bits >= sizeThreshold * 8) {
comp_size_bits = blkSize * 8;
}
// Update stats
compressionSize[std::ceil(std::log2(comp_size_bits))]++;
// Print debug information
DPRINTF(CacheComp, "Compressed cache line from %d to %d bits. " \
"Compression latency: %llu, decompression latency: %llu\n",
blkSize*8, comp_size_bits, comp_lat, decomp_lat);
}
Cycles
BaseCacheCompressor::getDecompressionLatency(const CacheBlk* blk) const
{
const CompressionBlk* comp_blk = static_cast<const CompressionBlk*>(blk);
// If block is compressed, return its decompression latency
if (comp_blk && comp_blk->isCompressed()){
const Cycles decomp_lat = comp_blk->getDecompressionLatency();
DPRINTF(CacheComp, "Decompressing block: %s (%d cycles)\n",
comp_blk->print(), decomp_lat);
return decomp_lat;
}
// Block is not compressed, so there is no decompression latency
return Cycles(0);
}
void
BaseCacheCompressor::setDecompressionLatency(CacheBlk* blk, const Cycles lat)
{
// Sanity check
assert(blk != nullptr);
// Assign latency
static_cast<CompressionBlk*>(blk)->setDecompressionLatency(lat);
}
void
BaseCacheCompressor::setSizeBits(CacheBlk* blk, const std::size_t size_bits)
{
// Sanity check
assert(blk != nullptr);
// Assign size
static_cast<CompressionBlk*>(blk)->setSizeBits(size_bits);
}
void
BaseCacheCompressor::regStats()
{
SimObject::regStats();
compressionSize
.init(std::log2(blkSize*8) + 1)
.name(name() + ".compression_size")
.desc("Number of blocks that were compressed to this power of" \
"two size.")
;
for (unsigned i = 0; i <= std::log2(blkSize*8); ++i) {
compressionSize.subname(i, std::to_string(1 << i));
compressionSize.subdesc(i, "Number of blocks that compressed to fit " \
"in " + std::to_string(1 << i) + " bits");
}
}
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