From d3c33d91b68e917478dba48c03a674b21ebd2747 Mon Sep 17 00:00:00 2001 From: Anthony Gutierrez Date: Tue, 14 May 2013 18:39:47 -0400 Subject: cpu: remove local/globalHistoryBits params from branch pred having separate params for the local/globalHistoryBits and the local/globalPredictorSize can lead to inconsistencies if they are not carefully set. this patch dervies the number of bits necessary to index into the local/global predictors based on their size. the value of the localHistoryTableSize for the ARM O3 CPU has been increased to 1024 from 64, which is more accurate for an A15 based on some correlation against A15 hardware. --- src/cpu/pred/BranchPredictor.py | 2 -- src/cpu/pred/tournament.cc | 21 ++++++++++++++------- 2 files changed, 14 insertions(+), 9 deletions(-) (limited to 'src/cpu/pred') diff --git a/src/cpu/pred/BranchPredictor.py b/src/cpu/pred/BranchPredictor.py index 21001b360..07fc840b8 100644 --- a/src/cpu/pred/BranchPredictor.py +++ b/src/cpu/pred/BranchPredictor.py @@ -40,10 +40,8 @@ class BranchPredictor(SimObject): localPredictorSize = Param.Unsigned(2048, "Size of local predictor") localCtrBits = Param.Unsigned(2, "Bits per counter") localHistoryTableSize = Param.Unsigned(2048, "Size of local history table") - localHistoryBits = Param.Unsigned(11, "Bits for the local history") globalPredictorSize = Param.Unsigned(8192, "Size of global predictor") globalCtrBits = Param.Unsigned(2, "Bits per counter") - globalHistoryBits = Param.Unsigned(13, "Bits of history") choicePredictorSize = Param.Unsigned(8192, "Size of choice predictor") choiceCtrBits = Param.Unsigned(2, "Bits of choice counters") diff --git a/src/cpu/pred/tournament.cc b/src/cpu/pred/tournament.cc index 52a05960f..e471d08f5 100644 --- a/src/cpu/pred/tournament.cc +++ b/src/cpu/pred/tournament.cc @@ -46,17 +46,28 @@ TournamentBP::TournamentBP(const Params *params) : BPredUnit(params), + localPredictorSize(params->localPredictorSize), localCtrBits(params->localCtrBits), localHistoryTableSize(params->localHistoryTableSize), - localHistoryBits(params->localHistoryBits), + localHistoryBits(ceilLog2(params->localPredictorSize)), globalPredictorSize(params->globalPredictorSize), globalCtrBits(params->globalCtrBits), - globalHistoryBits(params->globalHistoryBits), + globalHistoryBits( + ceilLog2(params->globalPredictorSize) > + ceilLog2(params->choicePredictorSize) ? + ceilLog2(params->globalPredictorSize) : + ceilLog2(params->choicePredictorSize)), choicePredictorSize(params->choicePredictorSize), choiceCtrBits(params->choiceCtrBits), instShiftAmt(params->instShiftAmt) { - localPredictorSize = ULL(1) << localHistoryBits; + if (!isPowerOf2(localPredictorSize)) { + fatal("Invalid local predictor size!\n"); + } + + if (!isPowerOf2(globalPredictorSize)) { + fatal("Invalid global predictor size!\n"); + } //Set up the array of counters for the local predictor localCtrs.resize(localPredictorSize); @@ -76,10 +87,6 @@ TournamentBP::TournamentBP(const Params *params) for (int i = 0; i < localHistoryTableSize; ++i) localHistoryTable[i] = 0; - if (!isPowerOf2(globalPredictorSize)) { - fatal("Invalid global predictor size!\n"); - } - //Setup the array of counters for the global predictor globalCtrs.resize(globalPredictorSize); -- cgit v1.2.3