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     struct MultiStats : public Stats::Group
  79     {
  80         const Multi& compressor;
  81
  82         MultiStats(BaseStats &base_group, Multi& _compressor);
  83
  84         void regStats() override;
  85
  86         /**
  87          * Number of times each compressor provided the nth best compression.
  88          */
  89         Stats::Vector2d ranks;
  90     } multiStats;
  91
  92   public:
  93     typedef MultiCompressorParams Params;
  94     Multi(const Params *p);
  95     ~Multi();
  96
  97     std::unique_ptr<Base::CompressionData> compress(
  98         const std::vector<Base::Chunk>& chunks,
  99         Cycles& comp_lat, Cycles& decomp_lat) override;
 100
 101     void decompress(const CompressionData* comp_data, uint64_t* data) override;
 102 };
 103
 104 class Multi::MultiCompData : public CompressionData
 105 {
 106   private:
 107     /** Index of the compressor that provided these compression results. */
 108     const uint8_t index;
 109
 110   public:
 111     /** Compression data of the best compressor. */
 112     std::unique_ptr<Base::CompressionData> compData;
 113
 114     /**
 115      * Default constructor.
 116      *
 117      * @param index Index of the compressor that provided this compression.
 118      * @param comp_data Compression data of the best compressor.
 119      */
 120     MultiCompData(unsigned index,
 121         std::unique_ptr<Base::CompressionData> comp_data);
 122
 123     /** Default destructor. */
 124     ~MultiCompData() = default;
 125
 126     /** Get the index of the best compressor. */
 127     uint8_t getIndex() const;
 128 };
 129
 130 } // namespace Compressor
 131
 132 #endif //__MEM_CACHE_COMPRESSORS_MULTI_HH__