sanchayanmaity/gem5
1
0
Fork 0
Code Issues Pull requests Packages Projects Releases Wiki Activity

cpu: remove local/globalHistoryBits params from branch pred

Browse source 
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.
This commit is contained in:
Anthony Gutierrez 2013-05-14 18:39:47 -04:00
parent 4e52789c6d
commit d3c33d91b6
3 changed files with 16 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

5
configs/common/O3_ARM_v7a.py
View file

@ -90,12 +90,11 @@ class O3_ARM_v7a_FUP(FUPool):
# Tournament Branch Predictor
class O3_ARM_v7a_BP(BranchPredictor):
predType = "tournament"
localPredictorSize = 2048
localCtrBits = 2
localHistoryTableSize = 64
localHistoryBits = 6
localHistoryTableSize = 1024
globalPredictorSize = 8192
globalCtrBits = 2
globalHistoryBits = 13
choicePredictorSize = 8192
choiceCtrBits = 2
BTBEntries = 2048

2
src/cpu/pred/BranchPredictor.py
View file

@ -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")

21
src/cpu/pred/tournament.cc
View file

@ -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);