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30 * Definition of a basic cache compressor.
33 #include "mem/cache/compressors/base.hh"
40 #include "base/trace.hh"
41 #include "debug/CacheComp.hh"
42 #include "mem/cache/tags/super_blk.hh"
43 #include "params/BaseCacheCompressor.hh"
45 // Uncomment this line if debugging compression
46 //#define DEBUG_COMPRESSION
48 BaseCacheCompressor::CompressionData::CompressionData()
53 BaseCacheCompressor::CompressionData::~CompressionData()
58 BaseCacheCompressor::CompressionData::setSizeBits(std::size_t size
)
64 BaseCacheCompressor::CompressionData::getSizeBits() const
70 BaseCacheCompressor::CompressionData::getSize() const
72 return std::ceil(_size
/8);
75 BaseCacheCompressor::BaseCacheCompressor(const Params
*p
)
76 : SimObject(p
), blkSize(p
->block_size
), sizeThreshold(p
->size_threshold
),
79 fatal_if(blkSize
< sizeThreshold
, "Compressed data must fit in a block");
83 BaseCacheCompressor::compress(const uint64_t* data
, Cycles
& comp_lat
,
84 Cycles
& decomp_lat
, std::size_t& comp_size_bits
)
87 std::unique_ptr
<CompressionData
> comp_data
=
88 compress(data
, comp_lat
, decomp_lat
);
90 // If we are in debug mode apply decompression just after the compression.
91 // If the results do not match, we've got an error
92 #ifdef DEBUG_COMPRESSION
93 uint64_t decomp_data
[blkSize
/8];
95 // Apply decompression
96 decompress(comp_data
.get(), decomp_data
);
98 // Check if decompressed line matches original cache line
99 fatal_if(std::memcmp(data
, decomp_data
, blkSize
),
100 "Decompressed line does not match original line.");
103 // Get compression size. If compressed size is greater than the size
104 // threshold, the compression is seen as unsuccessful
105 comp_size_bits
= comp_data
->getSizeBits();
106 if (comp_size_bits
>= sizeThreshold
* 8) {
107 comp_size_bits
= blkSize
* 8;
111 stats
.compressions
++;
112 stats
.compressionSizeBits
+= comp_size_bits
;
113 stats
.compressionSize
[std::ceil(std::log2(comp_size_bits
))]++;
115 // Print debug information
116 DPRINTF(CacheComp
, "Compressed cache line from %d to %d bits. " \
117 "Compression latency: %llu, decompression latency: %llu\n",
118 blkSize
*8, comp_size_bits
, comp_lat
, decomp_lat
);
122 BaseCacheCompressor::getDecompressionLatency(const CacheBlk
* blk
)
124 const CompressionBlk
* comp_blk
= static_cast<const CompressionBlk
*>(blk
);
126 // If block is compressed, return its decompression latency
127 if (comp_blk
&& comp_blk
->isCompressed()){
128 const Cycles decomp_lat
= comp_blk
->getDecompressionLatency();
129 DPRINTF(CacheComp
, "Decompressing block: %s (%d cycles)\n",
130 comp_blk
->print(), decomp_lat
);
131 stats
.decompressions
+= 1;
135 // Block is not compressed, so there is no decompression latency
140 BaseCacheCompressor::setDecompressionLatency(CacheBlk
* blk
, const Cycles lat
)
143 assert(blk
!= nullptr);
146 static_cast<CompressionBlk
*>(blk
)->setDecompressionLatency(lat
);
150 BaseCacheCompressor::setSizeBits(CacheBlk
* blk
, const std::size_t size_bits
)
153 assert(blk
!= nullptr);
156 static_cast<CompressionBlk
*>(blk
)->setSizeBits(size_bits
);
159 BaseCacheCompressor::BaseCacheCompressorStats::BaseCacheCompressorStats(
160 BaseCacheCompressor
& _compressor
)
161 : Stats::Group(&_compressor
), compressor(_compressor
),
162 compressions(this, "compressions",
163 "Total number of compressions"),
164 compressionSize(this, "compression_size",
165 "Number of blocks that were compressed to this power of two size"),
166 compressionSizeBits(this, "compression_size_bits",
167 "Total compressed data size, in bits"),
168 avgCompressionSizeBits(this, "avg_compression_size_bits",
169 "Average compression size, in bits"),
170 decompressions(this, "total_decompressions",
171 "Total number of decompressions")
176 BaseCacheCompressor::BaseCacheCompressorStats::regStats()
178 Stats::Group::regStats();
180 compressionSize
.init(std::log2(compressor
.blkSize
*8) + 1);
181 for (unsigned i
= 0; i
<= std::log2(compressor
.blkSize
*8); ++i
) {
182 std::string str_i
= std::to_string(1 << i
);
183 compressionSize
.subname(i
, str_i
);
184 compressionSize
.subdesc(i
,
185 "Number of blocks that compressed to fit in " + str_i
+ " bits");
188 avgCompressionSizeBits
.flags(Stats::total
| Stats::nozero
| Stats::nonan
);
189 avgCompressionSizeBits
= compressionSizeBits
/ compressions
;