frequent_values.hh

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/*
 * Copyright (c) 2019-2020 Inria
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#ifndef __MEM_CACHE_COMPRESSORS_FREQUENT_VALUES_HH__
#define __MEM_CACHE_COMPRESSORS_FREQUENT_VALUES_HH__
 
#include <climits>
#include <cstdint>
#include <memory>
#include <vector>
 
#include "base/cache/associative_cache.hh"
#include "base/sat_counter.hh"
#include "base/types.hh"
#include "mem/cache/base.hh"
#include "mem/cache/cache_probe_arg.hh"
#include "mem/cache/compressors/base.hh"
#include "mem/cache/compressors/encoders/huffman.hh"
#include "sim/eventq.hh"
#include "sim/probe/probe.hh"
 
namespace gem5
{
 
struct FrequentValuesCompressorParams;
 
namespace compression
{

class FrequentValues : public Base
{
  private:
    class CompData;
 
    using DataUpdate = CacheDataUpdateProbeArg;
 
    class FrequentValuesListener : public ProbeListenerArgBase<DataUpdate>
    {
      protected:
        FrequentValues &parent;
 
      public:
        FrequentValuesListener(FrequentValues &_parent, std::string name)
            : ProbeListenerArgBase(std::move(name)), parent(_parent)
        {
        }
        void notify(const DataUpdate &data_update) override;
    };
 
    std::vector<ProbeListenerPtr<FrequentValuesListener>> listeners;

    const bool useHuffmanEncoding;

    encoder::Huffman indexEncoder;

    const int counterBits;

    const Tick codeGenerationTicks;

    const bool checkSaturation;

    const unsigned numVFTEntries;

    const unsigned numSamples;

    unsigned takenSamples;

    enum Phase {SAMPLING, CODE_GENERATION, COMPRESSING};
    Phase phase;
 
    class VFTEntry : public CacheEntry
    {
      public:
        uint64_t value;

        SatCounter32 counter;
 
        VFTEntry(std::size_t num_bits, TagExtractor ext)
          : CacheEntry(ext), value(0), counter(num_bits)
        {
        }
 
        void
        invalidate() override
        {
            CacheEntry::invalidate();
            value = 0;
            counter.reset();
        }
    };

    AssociativeCache<VFTEntry> VFT;

    uint64_t uncompressedValue;

    EventFunctionWrapper codeGenerationEvent;

    void sampleValues(const std::vector<uint64_t> &data,
        bool is_invalidation);

    void generateCodes();
 
    std::unique_ptr<Base::CompressionData> compress(
        const std::vector<Chunk>& chunks, Cycles& comp_lat,
        Cycles& decomp_lat) override;
 
    void decompress(const CompressionData* comp_data, uint64_t* data) override;
 
  public:
    typedef FrequentValuesCompressorParams Params;
    FrequentValues(const Params &p);
    ~FrequentValues() = default;

    void probeNotify(const DataUpdate &data_update);
 
    void regProbeListeners() override;
};
 
class FrequentValues::CompData : public CompressionData
{
  public:
    struct CompressedValue
    {
        encoder::Code code;

        uint64_t value;
 
        CompressedValue(encoder::Code _code, uint64_t _value)
          : code(_code), value(_value)
        {
        }
    };

    std::vector<CompressedValue> compressedValues;
};
 
} // namespace compression
} // namespace gem5
 
#endif //__MEM_CACHE_COMPRESSORS_FREQUENT_VALUES_HH__