src/mem/cache/compressors/multi.hh

   1 /*
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  14  * this software without specific prior written permission.
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  28
  29 /** @file
  30  * Definition of the a multi compressor that choses the best compression
  31  * among multiple compressors.
  32  */
  33
  34 #ifndef __MEM_CACHE_COMPRESSORS_MULTI_HH__
  35 #define __MEM_CACHE_COMPRESSORS_MULTI_HH__
  36
  37 #include <cstdint>
  38 #include <vector>
  39
  40 #include "base/statistics.hh"
  41 #include "base/types.hh"
  42 #include "mem/cache/compressors/base.hh"
  43
  44 struct MultiCompressorParams;
  45
  46 namespace Compressor {
  47
  48 class Multi : public Base
  49 {
  50   protected:
  51     /**
  52      * Compression data for the multi compressor. It contains the compression
  53      * data of the best compressor, along with its index in the list of
  54      * sub-compressors.
  55      */
  56     class MultiCompData;
  57
  58     /** List of sub-compressors. */
  59     std::vector<Base*> compressors;
  60
  61     /**
  62      * An encoding is associated to each sub-compressor to inform which
  63      * sub-compressor to use when decompressing data. This information can
  64      * be added either to the tag entry, in which case no extra bits are
  65      * added to the compressed data (numEncodingBits = 0), or to the
  66      * compressed data itself.
  67      *
  68      * There is no encoding reserved for the uncompressed case; it is assumed
  69      * that an "is compressed" bit is stored in the tags. Therefore, even if
  70      * storing the encoding within the compressed data, these extra bits are
  71      * not added when the data is uncompressible.
  72      *
  73      * These extra bits are taken into account when thresholding the
  74      * compressed data's size.
  75      */
  76     const std::size_t numEncodingBits;
  77
  78     /**
  79      * Extra decompression latency to be added to the sub-compressor's
  80      * decompression latency. This can different from zero due to decoding,
  81      * shifting, or packaging, for example.
  82      */
  83     const Cycles extraDecompressionLatency;
  84
  85     struct MultiStats : public Stats::Group
  86     {
  87         const Multi& compressor;
  88
  89         MultiStats(BaseStats &base_group, Multi& _compressor);
  90
  91         void regStats() override;
  92
  93         /**
  94          * Number of times each compressor provided the nth best compression.
  95          */
  96         Stats::Vector2d ranks;
  97     } multiStats;
  98
  99   public:
 100     typedef MultiCompressorParams Params;
 101     Multi(const Params *p);
 102     ~Multi();
 103
 104     std::unique_ptr<Base::CompressionData> compress(
 105         const std::vector<Base::Chunk>& chunks,
 106         Cycles& comp_lat, Cycles& decomp_lat) override;
 107
 108     void decompress(const CompressionData* comp_data, uint64_t* data) override;
 109 };
 110
 111 class Multi::MultiCompData : public CompressionData
 112 {
 113   private:
 114     /** Index of the compressor that provided these compression results. */
 115     const uint8_t index;
 116
 117   public:
 118     /** Compression data of the best compressor. */
 119     std::unique_ptr<Base::CompressionData> compData;
 120
 121     /**
 122      * Default constructor.
 123      *
 124      * @param index Index of the compressor that provided this compression.
 125      * @param comp_data Compression data of the best compressor.
 126      */
 127     MultiCompData(unsigned index,
 128         std::unique_ptr<Base::CompressionData> comp_data);
 129
 130     /** Default destructor. */
 131     ~MultiCompData() = default;
 132
 133     /** Get the index of the best compressor. */
 134     uint8_t getIndex() const;
 135 };
 136
 137 } // namespace Compressor
 138
 139 #endif //__MEM_CACHE_COMPRESSORS_MULTI_HH__