src/mem/cache/compressors/base.cc - public/gem5 - Git at Google

 /*
  * Copyright (c) 2018-2020 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.
  */

 /** @file
  * Definition of a basic cache compressor.
  */

 #include "mem/cache/compressors/base.hh"

 #include <algorithm>
 #include <climits>
 #include <cmath>
 #include <cstdint>
 #include <string>

 #include "base/logging.hh"
 #include "base/trace.hh"
 #include "debug/CacheComp.hh"
 #include "mem/cache/base.hh"
 #include "mem/cache/tags/super_blk.hh"
 #include "params/BaseCacheCompressor.hh"

 namespace gem5
 {

 GEM5_DEPRECATED_NAMESPACE(Compressor, compression);
 namespace compression
 {

 // Uncomment this line if debugging compression
 //#define DEBUG_COMPRESSION

 Base::CompressionData::CompressionData()
     : _size(0)
 {
 }

 Base::CompressionData::~CompressionData()
 {
 }

 void
 Base::CompressionData::setSizeBits(std::size_t size)
 {
     _size = size;
 }

 std::size_t
 Base::CompressionData::getSizeBits() const
 {
     return _size;
 }

 std::size_t
 Base::CompressionData::getSize() const
 {
     return std::ceil(_size/8);
 }

 Base::Base(const Params &p)
   : SimObject(p), blkSize(p.block_size), chunkSizeBits(p.chunk_size_bits),
     sizeThreshold((blkSize * p.size_threshold_percentage) / 100),
     compChunksPerCycle(p.comp_chunks_per_cycle),
     compExtraLatency(p.comp_extra_latency),
     decompChunksPerCycle(p.decomp_chunks_per_cycle),
     decompExtraLatency(p.decomp_extra_latency),
     cache(nullptr), stats(*this)
 {
     fatal_if(64 % chunkSizeBits,
         "64 must be a multiple of the chunk granularity.");

     fatal_if(((CHAR_BIT * blkSize) / chunkSizeBits) < compChunksPerCycle,
         "Compressor processes more chunks per cycle than the number of "
         "chunks in the input");
     fatal_if(((CHAR_BIT * blkSize) / chunkSizeBits) < decompChunksPerCycle,
         "Decompressor processes more chunks per cycle than the number of "
         "chunks in the input");

     fatal_if(blkSize < sizeThreshold, "Compressed data must fit in a block");
 }

 void
 Base::setCache(BaseCache *_cache)
 {
     assert(!cache);
     cache = _cache;
 }

 std::vector<Base::Chunk>
 Base::toChunks(const uint64_t* data) const
 {
     // Number of chunks in a 64-bit value
     const unsigned num_chunks_per_64 =
         (sizeof(uint64_t) * CHAR_BIT) / chunkSizeBits;

     // Turn a 64-bit array into a chunkSizeBits-array
     std::vector<Chunk> chunks((blkSize * CHAR_BIT) / chunkSizeBits, 0);
     for (int i = 0; i < chunks.size(); i++) {
         const int index_64 = std::floor(i / (double)num_chunks_per_64);
         const unsigned start = i % num_chunks_per_64;
         chunks[i] = bits(data[index_64],
             (start + 1) * chunkSizeBits - 1, start * chunkSizeBits);
     }

     return chunks;
 }

 void
 Base::fromChunks(const std::vector<Chunk>& chunks, uint64_t* data) const
 {
     // Number of chunks in a 64-bit value
     const unsigned num_chunks_per_64 =
         (sizeof(uint64_t) * CHAR_BIT) / chunkSizeBits;

     // Turn a chunkSizeBits-array into a 64-bit array
     std::memset(data, 0, blkSize);
     for (int i = 0; i < chunks.size(); i++) {
         const int index_64 = std::floor(i / (double)num_chunks_per_64);
         const unsigned start = i % num_chunks_per_64;
         replaceBits(data[index_64], (start + 1) * chunkSizeBits - 1,
             start * chunkSizeBits, chunks[i]);
     }
 }

 std::unique_ptr<Base::CompressionData>
 Base::compress(const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat)
 {
     // Apply compression
     std::unique_ptr<CompressionData> comp_data =
         compress(toChunks(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
     std::size_t comp_size_bits = comp_data->getSizeBits();
     if (comp_size_bits > sizeThreshold * CHAR_BIT) {
         comp_size_bits = blkSize * CHAR_BIT;
         comp_data->setSizeBits(comp_size_bits);
         stats.failedCompressions++;
     }

     // Update stats
     stats.compressions++;
     stats.compressionSizeBits += comp_size_bits;
     if (comp_size_bits != 0) {
         stats.compressionSize[1 + std::ceil(std::log2(comp_size_bits))]++;
     } else {
         stats.compressionSize[0]++;
     }

     // 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);

     return comp_data;
 }

 Cycles
 Base::getDecompressionLatency(const CacheBlk* blk)
 {
     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);
         stats.decompressions += 1;
         return decomp_lat;
     }

     // Block is not compressed, so there is no decompression latency
     return Cycles(0);
 }

 void
 Base::setDecompressionLatency(CacheBlk* blk, const Cycles lat)
 {
     // Sanity check
     assert(blk != nullptr);

     // Assign latency
     static_cast<CompressionBlk*>(blk)->setDecompressionLatency(lat);
 }

 void
 Base::setSizeBits(CacheBlk* blk, const std::size_t size_bits)
 {
     // Sanity check
     assert(blk != nullptr);

     // Assign size
     static_cast<CompressionBlk*>(blk)->setSizeBits(size_bits);
 }

 Base::BaseStats::BaseStats(Base& _compressor)
   : statistics::Group(&_compressor), compressor(_compressor),
     ADD_STAT(compressions, statistics::units::Count::get(),
              "Total number of compressions"),
     ADD_STAT(failedCompressions, statistics::units::Count::get(),
              "Total number of failed compressions"),
     ADD_STAT(compressionSize, statistics::units::Count::get(),
              "Number of blocks that were compressed to this power of two "
              "size"),
     ADD_STAT(compressionSizeBits, statistics::units::Bit::get(),
              "Total compressed data size"),
     ADD_STAT(avgCompressionSizeBits, statistics::units::Rate<
                 statistics::units::Bit, statistics::units::Count>::get(),
              "Average compression size"),
     ADD_STAT(decompressions, statistics::units::Count::get(),
              "Total number of decompressions")
 {
 }

 void
 Base::BaseStats::regStats()
 {
     statistics::Group::regStats();

     // Values comprised are {0, 1, 2, 4, ..., blkSize}
     compressionSize.init(std::log2(compressor.blkSize*8) + 2);
     compressionSize.subname(0, "0");
     compressionSize.subdesc(0,
         "Number of blocks that compressed to fit in 0 bits");
     for (unsigned i = 0; i <= std::log2(compressor.blkSize*8); ++i) {
         std::string str_i = std::to_string(1 << i);
         compressionSize.subname(1+i, str_i);
         compressionSize.subdesc(1+i,
             "Number of blocks that compressed to fit in " + str_i + " bits");
     }

     avgCompressionSizeBits.flags(statistics::total | statistics::nozero |
         statistics::nonan);
     avgCompressionSizeBits = compressionSizeBits / compressions;
 }

 } // namespace compression
 } // namespace gem5
	/*
	* Copyright (c) 2018-2020 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.
	*/

	/** @file
	* Definition of a basic cache compressor.
	*/

	#include "mem/cache/compressors/base.hh"

	#include <algorithm>
	#include <climits>
	#include <cmath>
	#include <cstdint>
	#include <string>

	#include "base/logging.hh"
	#include "base/trace.hh"
	#include "debug/CacheComp.hh"
	#include "mem/cache/base.hh"
	#include "mem/cache/tags/super_blk.hh"
	#include "params/BaseCacheCompressor.hh"

	namespace gem5
	{

	GEM5_DEPRECATED_NAMESPACE(Compressor, compression);
	namespace compression
	{

	// Uncomment this line if debugging compression
	//#define DEBUG_COMPRESSION

	Base::CompressionData::CompressionData()
	: _size(0)
	{
	}

	Base::CompressionData::~CompressionData()
	{
	}

	void
	Base::CompressionData::setSizeBits(std::size_t size)
	{
	_size = size;
	}

	std::size_t
	Base::CompressionData::getSizeBits() const
	{
	return _size;
	}

	std::size_t
	Base::CompressionData::getSize() const
	{
	return std::ceil(_size/8);
	}

	Base::Base(const Params &p)
	: SimObject(p), blkSize(p.block_size), chunkSizeBits(p.chunk_size_bits),
	sizeThreshold((blkSize * p.size_threshold_percentage) / 100),
	compChunksPerCycle(p.comp_chunks_per_cycle),
	compExtraLatency(p.comp_extra_latency),
	decompChunksPerCycle(p.decomp_chunks_per_cycle),
	decompExtraLatency(p.decomp_extra_latency),
	cache(nullptr), stats(*this)
	{
	fatal_if(64 % chunkSizeBits,
	"64 must be a multiple of the chunk granularity.");

	fatal_if(((CHAR_BIT * blkSize) / chunkSizeBits) < compChunksPerCycle,
	"Compressor processes more chunks per cycle than the number of "
	"chunks in the input");
	fatal_if(((CHAR_BIT * blkSize) / chunkSizeBits) < decompChunksPerCycle,
	"Decompressor processes more chunks per cycle than the number of "
	"chunks in the input");

	fatal_if(blkSize < sizeThreshold, "Compressed data must fit in a block");
	}

	void
	Base::setCache(BaseCache *_cache)
	{
	assert(!cache);
	cache = _cache;
	}

	std::vector<Base::Chunk>
	Base::toChunks(const uint64_t* data) const
	{
	// Number of chunks in a 64-bit value
	const unsigned num_chunks_per_64 =
	(sizeof(uint64_t) * CHAR_BIT) / chunkSizeBits;

	// Turn a 64-bit array into a chunkSizeBits-array
	std::vector<Chunk> chunks((blkSize * CHAR_BIT) / chunkSizeBits, 0);
	for (int i = 0; i < chunks.size(); i++) {
	const int index_64 = std::floor(i / (double)num_chunks_per_64);
	const unsigned start = i % num_chunks_per_64;
	chunks[i] = bits(data[index_64],
	(start + 1) * chunkSizeBits - 1, start * chunkSizeBits);
	}

	return chunks;
	}

	void
	Base::fromChunks(const std::vector<Chunk>& chunks, uint64_t* data) const
	{
	// Number of chunks in a 64-bit value
	const unsigned num_chunks_per_64 =
	(sizeof(uint64_t) * CHAR_BIT) / chunkSizeBits;

	// Turn a chunkSizeBits-array into a 64-bit array
	std::memset(data, 0, blkSize);
	for (int i = 0; i < chunks.size(); i++) {
	const int index_64 = std::floor(i / (double)num_chunks_per_64);
	const unsigned start = i % num_chunks_per_64;
	replaceBits(data[index_64], (start + 1) * chunkSizeBits - 1,
	start * chunkSizeBits, chunks[i]);
	}
	}

	std::unique_ptr<Base::CompressionData>
	Base::compress(const uint64_t* data, Cycles& comp_lat, Cycles& decomp_lat)
	{
	// Apply compression
	std::unique_ptr<CompressionData> comp_data =
	compress(toChunks(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
	std::size_t comp_size_bits = comp_data->getSizeBits();
	if (comp_size_bits > sizeThreshold * CHAR_BIT) {
	comp_size_bits = blkSize * CHAR_BIT;
	comp_data->setSizeBits(comp_size_bits);
	stats.failedCompressions++;
	}

	// Update stats
	stats.compressions++;
	stats.compressionSizeBits += comp_size_bits;
	if (comp_size_bits != 0) {
	stats.compressionSize[1 + std::ceil(std::log2(comp_size_bits))]++;
	} else {
	stats.compressionSize[0]++;
	}

	// 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);

	return comp_data;
	}

	Cycles
	Base::getDecompressionLatency(const CacheBlk* blk)
	{
	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);
	stats.decompressions += 1;
	return decomp_lat;
	}

	// Block is not compressed, so there is no decompression latency
	return Cycles(0);
	}

	void
	Base::setDecompressionLatency(CacheBlk* blk, const Cycles lat)
	{
	// Sanity check
	assert(blk != nullptr);

	// Assign latency
	static_cast<CompressionBlk*>(blk)->setDecompressionLatency(lat);
	}

	void
	Base::setSizeBits(CacheBlk* blk, const std::size_t size_bits)
	{
	// Sanity check
	assert(blk != nullptr);

	// Assign size
	static_cast<CompressionBlk*>(blk)->setSizeBits(size_bits);
	}

	Base::BaseStats::BaseStats(Base& _compressor)
	: statistics::Group(&_compressor), compressor(_compressor),
	ADD_STAT(compressions, statistics::units::Count::get(),
	"Total number of compressions"),
	ADD_STAT(failedCompressions, statistics::units::Count::get(),
	"Total number of failed compressions"),
	ADD_STAT(compressionSize, statistics::units::Count::get(),
	"Number of blocks that were compressed to this power of two "
	"size"),
	ADD_STAT(compressionSizeBits, statistics::units::Bit::get(),
	"Total compressed data size"),
	ADD_STAT(avgCompressionSizeBits, statistics::units::Rate<
	statistics::units::Bit, statistics::units::Count>::get(),
	"Average compression size"),
	ADD_STAT(decompressions, statistics::units::Count::get(),
	"Total number of decompressions")
	{
	}

	void
	Base::BaseStats::regStats()
	{
	statistics::Group::regStats();

	// Values comprised are {0, 1, 2, 4, ..., blkSize}
	compressionSize.init(std::log2(compressor.blkSize*8) + 2);
	compressionSize.subname(0, "0");
	compressionSize.subdesc(0,
	"Number of blocks that compressed to fit in 0 bits");
	for (unsigned i = 0; i <= std::log2(compressor.blkSize*8); ++i) {
	std::string str_i = std::to_string(1 << i);
	compressionSize.subname(1+i, str_i);
	compressionSize.subdesc(1+i,
	"Number of blocks that compressed to fit in " + str_i + " bits");
	}

	avgCompressionSizeBits.flags(statistics::total \| statistics::nozero \|
	statistics::nonan);
	avgCompressionSizeBits = compressionSizeBits / compressions;
	}

	} // namespace compression
	} // namespace gem5