Cheri-research/Toooba
1
0
Fork 0
Code Issues 1 Pull Requests Actions Packages Projects Releases Wiki Activity

Timing optimisation for Tournament Predictor.

Browse Source 
Start global-history-indexed lookups in the previous cycle.
This is a general timing optimisation that should be pushed upstream at
some point.
This commit is contained in:
Jonathan Woodruff
2022-01-12 16:08:33 +00:00
parent 1d6633f423
commit 37f6dbde93
2 changed files with 17 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
src_Core/RISCY_OOO/procs/lib/Btb.bsv
View File

@@ -131,7 +131,10 @@ module mkBtbCore(NextAddrPred#(hashSz))
// Start SupSizeX2 BTB lookups, but ensure to lookup in the appropriate
// bank for the alignment of each potential branch.
for (Integer i = 0; i < valueOf(SupSizeX2); i = i + 1) begin
BtbAddr a = unpack(pack(getBtbAddr(pc)) + fromInteger(i));
// Only add lower bits for timing.
BtbAddr a = getBtbAddr(pc);
a = unpack({a.tag, {a.index,a.bank} + fromInteger(i)});
//BtbAddr a = unpack(pack(getBtbAddr(pc)) + fromInteger(i));
fullRecords[a.bank].lookupStart(MapKeyIndex{key: hash(a.tag), index: a.index});
compressedRecords[a.bank].lookupStart(MapKeyIndex{key: hash(a.tag), index: a.index});
end

17
src_Core/RISCY_OOO/procs/lib/TourPred.bsv
View File

@@ -114,6 +114,8 @@ module mkTourPred(DirPredictor#(TourTrainInfo));
endfunction
TourGlobalHist curGHist = gHistReg.history; // global history: MSB is the latest branch
Reg#(Vector#(SupSize, Bool)) globalTakenVec <- mkRegU;
Reg#(Vector#(SupSize, Bool)) useLocalVec <- mkRegU;
Vector#(SupSize, DirPred#(TourTrainInfo)) predIfc;
for(Integer i = 0; i < valueof(SupSize); i = i+1) begin
@@ -127,12 +129,11 @@ module mkTourPred(DirPredictor#(TourTrainInfo));
// all previous branch in this cycle must be not taken
// otherwise this branch should be on wrong path
// because all inst in same cycle are fetched consecutively
TourGlobalHist globalHist = curGHist >> predCnt[i];
// get global prediction
Bool globalTaken = isTaken(globalBht.sub(globalHist));
Bool globalTaken = globalTakenVec[predCnt[i]];
// make choice
Bool useLocal = isTaken(choiceBht.sub(globalHist));
Bool useLocal = useLocalVec[predCnt[i]];
Bool taken = useLocal ? localTaken : globalTaken;
// record prediction
@@ -145,7 +146,7 @@ module mkTourPred(DirPredictor#(TourTrainInfo));
return DirPredResult {
taken: taken,
train: TourTrainInfo {
globalHist: globalHist,
globalHist: curGHist >> predCnt[i],
localHist: localHist,
globalTaken: globalTaken,
localTaken: localTaken
@@ -158,6 +159,14 @@ module mkTourPred(DirPredictor#(TourTrainInfo));
(* fire_when_enabled, no_implicit_conditions *)
rule canonGlobalHist;
gHistReg.addHistory(predRes[valueof(SupSize)], predCnt[valueof(SupSize)]);
// Buffer useLocalVec
// Reproduce next history; this would ideally be done in GlobalBrHistReg to avoid duplicating logic.
TourGlobalHist nHist = truncate({predRes[valueof(SupSize)], curGHist} >> predCnt[valueof(SupSize)]);
function Bool globalTakenLookup (Integer i) = isTaken(globalBht.sub(nHist >> i));
function Bool useLocalLookup (Integer i) = isTaken(choiceBht.sub(nHist >> i));
globalTakenVec <= genWith(globalTakenLookup);
useLocalVec <= genWith(useLocalLookup);
// Reset counters and prediction.
predRes[valueof(SupSize)] <= 0;
predCnt[valueof(SupSize)] <= 0;
endrule