diff options
Diffstat (limited to 'src/cpu/pred/BranchPredictor.py')
| -rw-r--r-- | src/cpu/pred/BranchPredictor.py | 265 |
1 files changed, 264 insertions, 1 deletions
diff --git a/src/cpu/pred/BranchPredictor.py b/src/cpu/pred/BranchPredictor.py index 1d5fd5eec..85b225c3b 100644 --- a/src/cpu/pred/BranchPredictor.py +++ b/src/cpu/pred/BranchPredictor.py @@ -118,7 +118,7 @@ class TAGEBase(SimObject): logUResetPeriod = Param.Unsigned(18, "Log period in number of branches to reset TAGE useful counters") numUseAltOnNa = Param.Unsigned(1, "Number of USE_ALT_ON_NA counters") - useAltOnNaBits = Param.Unsigned(4, "Size of the USE_ALT_ON_NA counter") + useAltOnNaBits = Param.Unsigned(4, "Size of the USE_ALT_ON_NA counter(s)") maxNumAlloc = Param.Unsigned(1, "Max number of TAGE entries allocted on mispredict") @@ -185,6 +185,96 @@ class LoopPredictor(SimObject): optionalAgeReset = Param.Bool(True, "Reset age bits optionally in some cases") +class TAGE_SC_L_TAGE(TAGEBase): + type = 'TAGE_SC_L_TAGE' + cxx_class = 'TAGE_SC_L_TAGE' + cxx_header = "cpu/pred/tage_sc_l.hh" + abstract = True + tagTableTagWidths = [0] + numUseAltOnNa = 16 + pathHistBits = 27 + maxNumAlloc = 2 + logUResetPeriod = 10 + useAltOnNaBits = 5 + # TODO No speculation implemented as of now + speculativeHistUpdate = False + + # This size does not set the final sizes of the tables (it is just used + # for some calculations) + # Instead, the number of TAGE entries comes from shortTagsTageEntries and + # longTagsTageEntries + logTagTableSize = Param.Unsigned("Log size of each tag table") + + shortTagsTageFactor = Param.Unsigned( + "Factor for calculating the total number of short tags TAGE entries") + + longTagsTageFactor = Param.Unsigned( + "Factor for calculating the total number of long tags TAGE entries") + + shortTagsSize = Param.Unsigned(8, "Size of the short tags") + + longTagsSize = Param.Unsigned("Size of the long tags") + + firstLongTagTable = Param.Unsigned("First table with long tags") + + truncatePathHist = Param.Bool(True, + "Truncate the path history to its configured size") + + +class TAGE_SC_L_TAGE_64KB(TAGE_SC_L_TAGE): + type = 'TAGE_SC_L_TAGE_64KB' + cxx_class = 'TAGE_SC_L_TAGE_64KB' + cxx_header = "cpu/pred/tage_sc_l_64KB.hh" + nHistoryTables = 36 + + minHist = 6 + maxHist = 3000 + + tagTableUBits = 1 + + logTagTableSizes = [13] + + # This is used to handle the 2-way associativity + # (all odd entries are set to one, and if the corresponding even entry + # is set to one, then there is a 2-way associativity for this pair) + # Entry 0 is for the bimodal and it is ignored + # Note: For this implementation, some odd entries are also set to 0 to save + # some bits + noSkip = [0,0,1,0,0,0,1,0,0,1,1,1,1,1,1,1,1,1,1, + 1,1,1,1,0,1,0,1,0,1,0,0,0,1,0,0,0,1] + + logTagTableSize = 10 + shortTagsTageFactor = 10 + longTagsTageFactor = 20 + + longTagsSize = 12 + + firstLongTagTable = 13 + +class TAGE_SC_L_TAGE_8KB(TAGE_SC_L_TAGE): + type = 'TAGE_SC_L_TAGE_8KB' + cxx_class = 'TAGE_SC_L_TAGE_8KB' + cxx_header = "cpu/pred/tage_sc_l_8KB.hh" + + nHistoryTables = 30 + + minHist = 4 + maxHist = 1000 + + logTagTableSize = 7 + shortTagsTageFactor = 9 + longTagsTageFactor = 17 + longTagsSize = 12 + + logTagTableSizes = [12] + + firstLongTagTable = 11 + + truncatePathHist = False + + noSkip = [0,0,1,0,1,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,0,1,0,1,0,1,0,1] + + tagTableUBits = 2 # LTAGE branch predictor as described in # https://www.irisa.fr/caps/people/seznec/L-TAGE.pdf @@ -196,4 +286,177 @@ class LTAGE(TAGE): cxx_header = "cpu/pred/ltage.hh" tage = LTAGE_TAGE() + loop_predictor = Param.LoopPredictor(LoopPredictor(), "Loop predictor") + +class TAGE_SC_L_LoopPredictor(LoopPredictor): + type = 'TAGE_SC_L_LoopPredictor' + cxx_class = 'TAGE_SC_L_LoopPredictor' + cxx_header = "cpu/pred/tage_sc_l.hh" + loopTableAgeBits = 4 + loopTableConfidenceBits = 4 + loopTableTagBits = 10 + loopTableIterBits = 10 + useSpeculation = False + useHashing = True + useDirectionBit = True + restrictAllocation = True + initialLoopIter = 0 + initialLoopAge = 7 + optionalAgeReset = False + +class StatisticalCorrector(SimObject): + type = 'StatisticalCorrector' + cxx_class = 'StatisticalCorrector' + cxx_header = "cpu/pred/statistical_corrector.hh" + abstract = True + + # Statistical corrector parameters + + numEntriesFirstLocalHistories = Param.Unsigned( + "Number of entries for first local histories") + + bwnb = Param.Unsigned("Num global backward branch GEHL lengths") + bwm = VectorParam.Int("Global backward branch GEHL lengths") + logBwnb = Param.Unsigned("Log num of global backward branch GEHL entries") + + lnb = Param.Unsigned("Num first local history GEHL lenghts") + lm = VectorParam.Int("First local history GEHL lengths") + logLnb = Param.Unsigned("Log number of first local history GEHL entries") + + inb = Param.Unsigned(1, "Num IMLI GEHL lenghts") + im = VectorParam.Int([8], "IMLI history GEHL lengths") + logInb = Param.Unsigned("Log number of IMLI GEHL entries") + + logBias = Param.Unsigned("Log size of Bias tables") + + logSizeUp = Param.Unsigned(6, + "Log size of update threshold counters tables") + + chooserConfWidth = Param.Unsigned(7, + "Number of bits for the chooser counters") + + updateThresholdWidth = Param.Unsigned(12, + "Number of bits for the update threshold counter") + + pUpdateThresholdWidth = Param.Unsigned(8, + "Number of bits for the pUpdate threshold counters") + + extraWeightsWidth = Param.Unsigned(6, + "Number of bits for the extra weights") + + scCountersWidth = Param.Unsigned(6, "Statistical corrector counters width") + +# TAGE-SC-L branch predictor as desribed in +# https://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf +# It is a modified LTAGE predictor plus a statistical corrector predictor +# The TAGE modifications include bank interleaving and partial associativity +# Two different sizes are proposed in the paper: +# 8KB => See TAGE_SC_L_8KB below +# 64KB => See TAGE_SC_L_64KB below +# The TAGE_SC_L_8KB and TAGE_SC_L_64KB classes differ not only on the values +# of some parameters, but also in some implementation details +# Given this, the TAGE_SC_L class is left abstract +# Note that as it is now, this branch predictor does not handle any type +# of speculation: All the structures/histories are updated at commit time +class TAGE_SC_L(LTAGE): + type = 'TAGE_SC_L' + cxx_class = 'TAGE_SC_L' + cxx_header = "cpu/pred/tage_sc_l.hh" + abstract = True + + statistical_corrector = Param.StatisticalCorrector( + "Statistical Corrector") + +class TAGE_SC_L_64KB_LoopPredictor(TAGE_SC_L_LoopPredictor): + logSizeLoopPred = 5 + +class TAGE_SC_L_8KB_LoopPredictor(TAGE_SC_L_LoopPredictor): + logSizeLoopPred = 3 + +class TAGE_SC_L_64KB_StatisticalCorrector(StatisticalCorrector): + type = 'TAGE_SC_L_64KB_StatisticalCorrector' + cxx_class = 'TAGE_SC_L_64KB_StatisticalCorrector' + cxx_header = "cpu/pred/tage_sc_l_64KB.hh" + + pnb = Param.Unsigned(3, "Num variation global branch GEHL lengths") + pm = VectorParam.Int([25, 16, 9], "Variation global branch GEHL lengths") + logPnb = Param.Unsigned(9, + "Log number of variation global branch GEHL entries") + + snb = Param.Unsigned(3, "Num second local history GEHL lenghts") + sm = VectorParam.Int([16, 11, 6], "Second local history GEHL lengths") + logSnb = Param.Unsigned(9, + "Log number of second local history GEHL entries") + + tnb = Param.Unsigned(2, "Num third local history GEHL lenghts") + tm = VectorParam.Int([9, 4], "Third local history GEHL lengths") + logTnb = Param.Unsigned(10, + "Log number of third local history GEHL entries") + + imnb = Param.Unsigned(2, "Num second IMLI GEHL lenghts") + imm = VectorParam.Int([10, 4], "Second IMLI history GEHL lengths") + logImnb = Param.Unsigned(9, "Log number of second IMLI GEHL entries") + + numEntriesSecondLocalHistories = Param.Unsigned(16, + "Number of entries for second local histories") + numEntriesThirdLocalHistories = Param.Unsigned(16, + "Number of entries for second local histories") + + numEntriesFirstLocalHistories = 256 + + logBias = 8 + + bwnb = 3 + bwm = [40, 24, 10] + logBwnb = 10 + + lnb = 3 + lm = [11, 6, 3] + logLnb = 10 + + logInb = 8 + +class TAGE_SC_L_8KB_StatisticalCorrector(StatisticalCorrector): + type = 'TAGE_SC_L_8KB_StatisticalCorrector' + cxx_class = 'TAGE_SC_L_8KB_StatisticalCorrector' + cxx_header = "cpu/pred/tage_sc_l_8KB.hh" + gnb = Param.Unsigned(2, "Num global branch GEHL lengths") + gm = VectorParam.Int([6, 3], "Global branch GEHL lengths") + logGnb = Param.Unsigned(7, "Log number of global branch GEHL entries") + + numEntriesFirstLocalHistories = 64 + + logBias = 7 + + bwnb = 2 + logBwnb = 7 + bwm = [16, 8] + + lnb = 2 + logLnb = 7 + lm = [6, 3] + + logInb = 7 + +# 64KB TAGE-SC-L branch predictor as described in +# http://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf +class TAGE_SC_L_64KB(TAGE_SC_L): + type = 'TAGE_SC_L_64KB' + cxx_class = 'TAGE_SC_L_64KB' + cxx_header = "cpu/pred/tage_sc_l_64KB.hh" + + tage = TAGE_SC_L_TAGE_64KB() + loop_predictor = TAGE_SC_L_64KB_LoopPredictor() + statistical_corrector = TAGE_SC_L_64KB_StatisticalCorrector() + +# 8KB TAGE-SC-L branch predictor as described in +# http://www.jilp.org/cbp2016/paper/AndreSeznecLimited.pdf +class TAGE_SC_L_8KB(TAGE_SC_L): + type = 'TAGE_SC_L_8KB' + cxx_class = 'TAGE_SC_L_8KB' + cxx_header = "cpu/pred/tage_sc_l_8KB.hh" + + tage = TAGE_SC_L_TAGE_8KB() + loop_predictor = TAGE_SC_L_8KB_LoopPredictor() + statistical_corrector = TAGE_SC_L_8KB_StatisticalCorrector() |