cpu-o3: Disabled two-taken, added override bubble perf counter (#309)

* cpu-o3: fix pendingEvents wakeup Change-Id: I43752e99026ce2e250f460bd78fcb6591bdacd98 * cpu-o3: Disabled two-taken, added override bubble perf counter This change disables the two-taken branch prediction at ideal configuration and adds a performance counter to track override bubbles. Change-Id: I3feb9bf662811941ad561ab73e0ee8c5b9040840 --------- Co-authored-by: lixin <[email protected]> Co-authored-by: xu boran <[email protected]>
OpenXiangShan · Mar 4, 2025 · d865947 · d865947
1 parent 529486a
commit d865947
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Showing 3 changed files with 7 additions and 3 deletions.
diff --git a/configs/example/xiangshan.py b/configs/example/xiangshan.py
@@ -346,7 +346,7 @@ def setKmhV3IdealParams(args, system):
 
         # ideal decoupled frontend
         if args.bp_type is None or args.bp_type == 'DecoupledBPUWithFTB':
-            cpu.branchPred.enableTwoTaken = True
+            cpu.branchPred.enableTwoTaken = False
             cpu.branchPred.numBr = 8    # numBr must be a power of 2, see getShuffledBrIndex()
             cpu.branchPred.predictWidth = 64
             cpu.branchPred.tage.enableSC = False # TODO(bug): When numBr changes, enabling SC will trigger an assert

diff --git a/src/cpu/pred/ftb/decoupled_bpred.cc b/src/cpu/pred/ftb/decoupled_bpred.cc
@@ -450,7 +450,9 @@ DecoupledBPUWithFTB::DBPFTBStats::DBPFTBStats(statistics::Group* parent, unsigne
     ADD_STAT(staticBranchNum, statistics::units::Count::get(), "the number of all (different) static branches"),
     ADD_STAT(staticBranchNumEverTaken, statistics::units::Count::get(), "the number of all (different) static branches that are once taken"),
     ADD_STAT(predsOfEachStage, statistics::units::Count::get(), "the number of preds of each stage that account for final pred"),
-    ADD_STAT(commitPredsFromEachStage, statistics::units::Count::get(), "the number of preds of each stage that account for a committed stream"),
+    ADD_STAT(overrideBubbleNum,  statistics::units::Count::get(), "the number of override bubbles"),
+    ADD_STAT(commitPredsFromEachStage, statistics::units::Count::get(),
+    "the number of preds of each stage that account for a committed stream"),
     ADD_STAT(fsqEntryDist, statistics::units::Count::get(), "the distribution of number of entries in fsq"),
     ADD_STAT(fsqEntryEnqueued, statistics::units::Count::get(), "the number of fsq entries enqueued"),
     ADD_STAT(fsqEntryCommitted, statistics::units::Count::get(), "the number of fsq entries committed at last"),
@@ -2125,6 +2127,7 @@ DecoupledBPUWithFTB::tryEnqFetchStream()
     if (numOverrideBubbles > 0) {
         DPRINTF(DecoupleBP, "Waiting for bubble caused by overriding, bubbles rest: %u\n", numOverrideBubbles);
         DPRINTF(Override, "Waiting for bubble caused by overriding, bubbles rest: %u\n", numOverrideBubbles);
+        dbpFtbStats.overrideBubbleNum++;
         return;
     }
     assert(!streamQueueFull());
@@ -2635,4 +2638,4 @@ DecoupledBPUWithFTB::getPreservedReturnAddr(const DynInstPtr &dynInst)
 
 }  // namespace branch_prediction
 
-}  // namespace gem5
+}  // namespace gem5
diff --git a/src/cpu/pred/ftb/decoupled_bpred.hh b/src/cpu/pred/ftb/decoupled_bpred.hh
@@ -402,6 +402,7 @@ class DecoupledBPUWithFTB : public BPredUnit
         statistics::Scalar staticBranchNumEverTaken;
 
         statistics::Vector predsOfEachStage;
+        statistics::Scalar overrideBubbleNum;
         statistics::Vector commitPredsFromEachStage;
         statistics::Distribution fsqEntryDist;
         statistics::Scalar fsqEntryEnqueued;