src/mem/cache/compressors/Compressors.py

# Copyright (c) 2018-2020 Inria
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from m5.params import *
from m5.proxy import *
from m5.SimObject import *

from m5.objects.IndexingPolicies import *
from m5.objects.ReplacementPolicies import *

class BaseCacheCompressor(SimObject):
    type = 'BaseCacheCompressor'
    abstract = True
    cxx_class = 'gem5::compression::Base'
    cxx_header = "mem/cache/compressors/base.hh"

    block_size = Param.Int(Parent.cache_line_size, "Block size in bytes")
    chunk_size_bits = Param.Unsigned(32,
        "Size of a parsing data chunk (in bits)")
    size_threshold_percentage = Param.Percent(50,
        "Minimum percentage of the block size, a compressed block must "
        "achieve to be stored in compressed format")

    comp_chunks_per_cycle = Param.Unsigned(1,
        "Number of chunks that can be compressed in parallel per cycle.")
    comp_extra_latency = Param.Cycles(1, "Number of extra cycles required "
        "to finish compression (e.g., due to shifting and packaging).")
    decomp_chunks_per_cycle = Param.Unsigned(1,
        "Number of chunks that can be decompressed in parallel per cycle.")
    decomp_extra_latency = Param.Cycles(1, "Number of extra cycles required "
        "to finish decompression (e.g., due to shifting and packaging).")

class BaseDictionaryCompressor(BaseCacheCompressor):
    type = 'BaseDictionaryCompressor'
    abstract = True
    cxx_class = 'gem5::compression::BaseDictionaryCompressor'
    cxx_header = "mem/cache/compressors/dictionary_compressor.hh"

    dictionary_size = Param.Int(Parent.cache_line_size,
        "Number of dictionary entries")

class Base64Delta8(BaseDictionaryCompressor):
    type = 'Base64Delta8'
    cxx_class = 'gem5::compression::Base64Delta8'
    cxx_header = "mem/cache/compressors/base_delta.hh"

    chunk_size_bits = 64

    # Base-delta compressors achieve 1-cycle latencies
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class Base64Delta16(BaseDictionaryCompressor):
    type = 'Base64Delta16'
    cxx_class = 'gem5::compression::Base64Delta16'
    cxx_header = "mem/cache/compressors/base_delta.hh"

    chunk_size_bits = 64

    # Base-delta compressors achieve 1-cycle latencies
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class Base64Delta32(BaseDictionaryCompressor):
    type = 'Base64Delta32'
    cxx_class = 'gem5::compression::Base64Delta32'
    cxx_header = "mem/cache/compressors/base_delta.hh"

    chunk_size_bits = 64

    # Base-delta compressors achieve 1-cycle latencies
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class Base32Delta8(BaseDictionaryCompressor):
    type = 'Base32Delta8'
    cxx_class = 'gem5::compression::Base32Delta8'
    cxx_header = "mem/cache/compressors/base_delta.hh"

    chunk_size_bits = 32

    # Base-delta compressors achieve 1-cycle latencies
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class Base32Delta16(BaseDictionaryCompressor):
    type = 'Base32Delta16'
    cxx_class = 'gem5::compression::Base32Delta16'
    cxx_header = "mem/cache/compressors/base_delta.hh"

    chunk_size_bits = 32

    # Base-delta compressors achieve 1-cycle latencies
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class Base16Delta8(BaseDictionaryCompressor):
    type = 'Base16Delta8'
    cxx_class = 'gem5::compression::Base16Delta8'
    cxx_header = "mem/cache/compressors/base_delta.hh"

    chunk_size_bits = 16

    # Base-delta compressors achieve 1-cycle latencies
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class CPack(BaseDictionaryCompressor):
    type = 'CPack'
    cxx_class = 'gem5::compression::CPack'
    cxx_header = "mem/cache/compressors/cpack.hh"

    comp_chunks_per_cycle = 2
    # Accounts for pattern matching, length generation, packaging and shifting
    comp_extra_latency = 5
    decomp_chunks_per_cycle = 2
    decomp_extra_latency = 1

class FPC(BaseDictionaryCompressor):
    type = 'FPC'
    cxx_class = 'gem5::compression::FPC'
    cxx_header = "mem/cache/compressors/fpc.hh"

    comp_chunks_per_cycle = 8
    comp_extra_latency = 1
    decomp_chunks_per_cycle = 4
    decomp_extra_latency = 1

    # Dummy dictionary size, since FPC has no dictionary
    dictionary_size = 1

    zero_run_bits = Param.Int(3, "Number of bits of the zero run bit field")

class FPCD(BaseDictionaryCompressor):
    type = 'FPCD'
    cxx_class = 'gem5::compression::FPCD'
    cxx_header = "mem/cache/compressors/fpcd.hh"

    # Accounts for checking all patterns, selecting patterns, and shifting
    # The original claim of a decompression latency of 2 cycles would likely
    # generate an unrealistically complex circuit
    comp_chunks_per_cycle = 4
    comp_extra_latency = 1
    decomp_chunks_per_cycle = 4
    decomp_extra_latency = 0

    dictionary_size = 2

class FrequentValuesCompressor(BaseCacheCompressor):
    type = 'FrequentValuesCompressor'
    cxx_class = 'gem5::compression::FrequentValues'
    cxx_header = "mem/cache/compressors/frequent_values.hh"

    chunk_size_bits = 32
    code_generation_ticks = Param.Unsigned(10000, "Number of elapsed " \
        "ticks until the samples are analyzed and their codes are generated.")
    # @todo The width of a counter width is determined by the maximum
    # number of times a given value appears in the cache - i.e.,
    # log2(cache_size/chunk_size_bits))".
    counter_bits = Param.Unsigned(18, "Number of bits per frequency counter.")
    max_code_length = Param.Unsigned(18, "Maximum number of bits in a "
        "codeword. If 0, table indices are not encoded.")
    num_samples = Param.Unsigned(100000, "Number of samples that must be " \
        "taken before compression is effectively used.")
    check_saturation = Param.Bool(False, "Whether the counters should be " \
        "manipulated in case of saturation.")

    vft_assoc = Param.Int(16, "Associativity of the VFT.")
    vft_entries = Param.MemorySize("1024", "Number of entries of the VFT.")
    vft_indexing_policy = Param.BaseIndexingPolicy(
        SetAssociative(entry_size = 1, assoc = Parent.vft_assoc,
        size = Parent.vft_entries), "Indexing policy of the VFT.")
    vft_replacement_policy = Param.BaseReplacementPolicy(LFURP(),
        "Replacement policy of the VFT.")

    comp_chunks_per_cycle = 1
    comp_extra_latency = 1
    decomp_chunks_per_cycle = 1
    decomp_extra_latency = 0

class MultiCompressor(BaseCacheCompressor):
    type = 'MultiCompressor'
    cxx_class = 'gem5::compression::Multi'
    cxx_header = "mem/cache/compressors/multi.hh"

    # Dummy default compressor list. This might not be an optimal choice,
    # since these compressors have many overlapping patterns
    compressors = VectorParam.BaseCacheCompressor([CPack(), FPCD()],
        "Array of compressors")
    encoding_in_tags = Param.Bool(False, "If set the bits to inform which "
        "sub-compressor compressed some data are added to its corresponding "
        "tag entry.")

    # Use the sub-compressors' latencies
    comp_chunks_per_cycle = 0
    decomp_chunks_per_cycle = 0

    # Assume extra 1 cycle to select the results of the winning sub-compressor
    comp_extra_latency = 1

    # Multi-compressors may need a couple of extra cycles to the select
    # which sub-compressor should be used to decompress the data
    decomp_extra_latency = 1

class PerfectCompressor(BaseCacheCompressor):
    type = 'PerfectCompressor'
    cxx_class = 'gem5::compression::Perfect'
    cxx_header = "mem/cache/compressors/perfect.hh"

    chunk_size_bits = 64

    max_compression_ratio = Param.Int("Maximum compression ratio allowed")

    # In a perfect world compression and decompression happen in 1 cycle
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class RepeatedQwordsCompressor(BaseDictionaryCompressor):
    type = 'RepeatedQwordsCompressor'
    cxx_class = 'gem5::compression::RepeatedQwords'
    cxx_header = "mem/cache/compressors/repeated_qwords.hh"

    chunk_size_bits = 64

    # Assume 1-cycle latencies
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class ZeroCompressor(BaseDictionaryCompressor):
    type = 'ZeroCompressor'
    cxx_class = 'gem5::compression::Zero'
    cxx_header = "mem/cache/compressors/zero.hh"

    chunk_size_bits = 64

    # Assume 1-cycle latencies
    comp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    comp_extra_latency = 0
    decomp_chunks_per_cycle = 8 * Self.block_size / Self.chunk_size_bits
    decomp_extra_latency = 0

class BDI(MultiCompressor):
    compressors = [
        ZeroCompressor(size_threshold_percentage=99),
        RepeatedQwordsCompressor(size_threshold_percentage=99),
        Base64Delta8(size_threshold_percentage=99),
        Base64Delta16(size_threshold_percentage=99),
        Base64Delta32(size_threshold_percentage=99),
        Base32Delta8(size_threshold_percentage=99),
        Base32Delta16(size_threshold_percentage=99),
        Base16Delta8(size_threshold_percentage=99),
    ]

    # By default assume that the encoding is stored in the tags, and is
    # retrieved and decoded while (and ends before) the data is being read.
    decomp_extra_latency = 0
    encoding_in_tags=True