src/cpu/pred/BranchPredictor.py

   1 # Copyright (c) 2012 Mark D. Hill and David A. Wood
   2 # Copyright (c) 2015 The University of Wisconsin
   3 # All rights reserved.
   4 #
   5 # Redistribution and use in source and binary forms, with or without
   6 # modification, are permitted provided that the following conditions are
   7 # met: redistributions of source code must retain the above copyright
   8 # notice, this list of conditions and the following disclaimer;
   9 # redistributions in binary form must reproduce the above copyright
  10 # notice, this list of conditions and the following disclaimer in the
  11 # documentation and/or other materials provided with the distribution;
  12 # neither the name of the copyright holders nor the names of its
  13 # contributors may be used to endorse or promote products derived from
  14 # this software without specific prior written permission.
  15 #
  16 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19 # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21 # SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23 # DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24 # THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27 #
  28 # Authors: Nilay Vaish and Dibakar Gope
  29
  30 from m5.SimObject import SimObject
  31 from m5.params import *
  32
  33 class BranchPredictor(SimObject):
  34     type = 'BranchPredictor'
  35     cxx_class = 'BPredUnit'
  36     cxx_header = "cpu/pred/bpred_unit.hh"
  37     abstract = True
  38
  39     numThreads = Param.Unsigned(1, "Number of threads")
  40     BTBEntries = Param.Unsigned(4096, "Number of BTB entries")
  41     BTBTagSize = Param.Unsigned(16, "Size of the BTB tags, in bits")
  42     RASSize = Param.Unsigned(16, "RAS size")
  43     instShiftAmt = Param.Unsigned(2, "Number of bits to shift instructions by")
  44
  45     useIndirect = Param.Bool(True, "Use indirect branch predictor")
  46     indirectHashGHR = Param.Bool(True, "Hash branch predictor GHR")
  47     indirectHashTargets = Param.Bool(True, "Hash path history targets")
  48     indirectSets = Param.Unsigned(256, "Cache sets for indirect predictor")
  49     indirectWays = Param.Unsigned(2, "Ways for indirect predictor")
  50     indirectTagSize = Param.Unsigned(16, "Indirect target cache tag bits")
  51     indirectPathLength = Param.Unsigned(3,
  52         "Previous indirect targets to use for path history")
  53
  54
  55
  56 class LocalBP(BranchPredictor):
  57     type = 'LocalBP'
  58     cxx_class = 'LocalBP'
  59     cxx_header = "cpu/pred/2bit_local.hh"
  60
  61     localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
  62     localCtrBits = Param.Unsigned(2, "Bits per counter")
  63
  64
  65 class TournamentBP(BranchPredictor):
  66     type = 'TournamentBP'
  67     cxx_class = 'TournamentBP'
  68     cxx_header = "cpu/pred/tournament.hh"
  69
  70     localPredictorSize = Param.Unsigned(2048, "Size of local predictor")
  71     localCtrBits = Param.Unsigned(2, "Bits per counter")
  72     localHistoryTableSize = Param.Unsigned(2048, "size of local history table")
  73     globalPredictorSize = Param.Unsigned(8192, "Size of global predictor")
  74     globalCtrBits = Param.Unsigned(2, "Bits per counter")
  75     choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
  76     choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")
  77
  78
  79 class BiModeBP(BranchPredictor):
  80     type = 'BiModeBP'
  81     cxx_class = 'BiModeBP'
  82     cxx_header = "cpu/pred/bi_mode.hh"
  83
  84     globalPredictorSize = Param.Unsigned(8192, "Size of global predictor")
  85     globalCtrBits = Param.Unsigned(2, "Bits per counter")
  86     choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor")
  87     choiceCtrBits = Param.Unsigned(2, "Bits of choice counters")
  88
  89 class LTAGE(BranchPredictor):
  90     type = 'LTAGE'
  91     cxx_class = 'LTAGE'
  92     cxx_header = "cpu/pred/ltage.hh"
  93
  94     logSizeBiMP = Param.Unsigned(14, "Log size of Bimodal predictor in bits")
  95     logSizeTagTables = Param.Unsigned(11, "Log size of tag table in LTAGE")
  96     logSizeLoopPred = Param.Unsigned(8, "Log size of the loop predictor")
  97     nHistoryTables = Param.Unsigned(12, "Number of history tables")
  98     tagTableCounterBits = Param.Unsigned(3, "Number of tag table counter bits")
  99     histBufferSize = Param.Unsigned(2097152,
 100             "A large number to track all branch histories(2MEntries default)")
 101     minHist = Param.Unsigned(4, "Minimum history size of LTAGE")
 102     maxHist = Param.Unsigned(640, "Maximum history size of LTAGE")
 103     minTagWidth = Param.Unsigned(7, "Minimum tag size in tag tables")
 104