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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.
* A cache compressor must consist of a compression and a decompression
* methods. It must also be aware of the size of an uncompressed cache
* line.
*/
#ifndef __MEM_CACHE_COMPRESSORS_BASE_HH__
#define __MEM_CACHE_COMPRESSORS_BASE_HH__
#include <cstdint>
#include "base/statistics.hh"
#include "base/types.hh"
#include "sim/sim_object.hh"
class CacheBlk;
struct BaseCacheCompressorParams;
/**
* Base cache compressor interface. Every cache compressor must implement a
* compression and a decompression method.
*/
class BaseCacheCompressor : public SimObject
{
protected:
/**
* This compressor must be able to access the protected functions of
* its sub-compressors.
*/
friend class MultiCompressor;
/**
* Forward declaration of compression data. Every new compressor must
* create a new compression data based on it.
*/
class CompressionData;
/**
* Uncompressed cache line size (in bytes).
*/
const std::size_t blkSize;
/**
* Size in bytes at which a compression is classified as bad and therefore
* the compressed block is restored to its uncompressed format.
*/
const std::size_t sizeThreshold;
struct BaseCacheCompressorStats : public Stats::Group
{
const BaseCacheCompressor& compressor;
BaseCacheCompressorStats(BaseCacheCompressor& compressor);
void regStats() override;
/** Number of compressions performed. */
Stats::Scalar compressions;
/** Number of blocks that were compressed to this power of two size. */
Stats::Vector compressionSize;
/** Total compressed data size, in number of bits. */
Stats::Scalar compressionSizeBits;
/** Average data size after compression, in number of bits. */
Stats::Formula avgCompressionSizeBits;
/** Number of decompressions performed. */
Stats::Scalar decompressions;
} stats;
/**
* Apply the compression process to the cache line.
* Returns the number of cycles used by the compressor, however it is
* usually covered by a good pipelined execution, and is currently ignored.
* The decompression latency is also returned, in order to avoid
* increasing simulation time and memory consumption.
*
* @param cache_line The cache line to be compressed.
* @param comp_lat Compression latency in number of cycles.
* @param decomp_lat Decompression latency in number of cycles.
* @return Cache line after compression.
*/
virtual std::unique_ptr<CompressionData> compress(
const uint64_t* cache_line, Cycles& comp_lat, Cycles& decomp_lat) = 0;
/**
* Apply the decompression process to the compressed data.
*
* @param comp_data Compressed cache line.
* @param cache_line The cache line to be decompressed.
*/
virtual void decompress(const CompressionData* comp_data,
uint64_t* cache_line) = 0;
public:
/** Convenience typedef. */
typedef BaseCacheCompressorParams Params;
/**
* Default constructor.
*/
BaseCacheCompressor(const Params *p);
/**
* Default destructor.
*/
virtual ~BaseCacheCompressor() {};
/**
* Apply the compression process to the cache line. Ignores compression
* cycles.
*
* @param data The cache line to be compressed.
* @param comp_lat Compression latency in number of cycles.
* @param decomp_lat Decompression latency in number of cycles.
* @param comp_size_bits Compressed data size (in bits).
*/
void compress(const uint64_t* data, Cycles& comp_lat,
Cycles& decomp_lat, std::size_t& comp_size_bits);
/**
* Get the decompression latency if the block is compressed. Latency is 0
* otherwise.
*
* @param blk The compressed block.
*/
Cycles getDecompressionLatency(const CacheBlk* blk);
/**
* Set the decompression latency of compressed block.
*
* @param blk The compressed block.
* @param lat The decompression latency.
*/
static void setDecompressionLatency(CacheBlk* blk, const Cycles lat);
/**
* Set the size of the compressed block, in bits.
*
* @param blk The compressed block.
* @param size_bits The block size.
*/
static void setSizeBits(CacheBlk* blk, const std::size_t size_bits);
};
class BaseCacheCompressor::CompressionData {
private:
/**
* Compressed cache line size (in bits).
*/
std::size_t _size;
public:
/**
* Default constructor.
*/
CompressionData();
/**
* Virtual destructor. Without it unique_ptr will cause mem leak.
*/
virtual ~CompressionData();
/**
* Set compression size (in bits).
*
* @param size Compressed data size.
*/
void setSizeBits(std::size_t size);
/**
* Get compression size (in bits).
*
* @return Compressed data size.
*/
std::size_t getSizeBits() const;
/**
* Get compression size (in bytes).
*
* @return Compressed data size.
*/
std::size_t getSize() const;
};
#endif //__MEM_CACHE_COMPRESSORS_BASE_HH__
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