cpu: Added new stats to TAGE and LTAGE branch predictors
They are basically used to tell wich component of the predictor is
providing the prediction and whether it is correct or wrong
Change-Id: I7b3db66535f159091f1b37d70c2d942d50b20fb2
Signed-off-by: Pau Cabre <pau.cabre@metempsy.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14535
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>
diff --git a/src/cpu/pred/ltage.cc b/src/cpu/pred/ltage.cc
index 3be0193..73f4777 100644
--- a/src/cpu/pred/ltage.cc
+++ b/src/cpu/pred/ltage.cc
@@ -228,6 +228,7 @@
if ((loopUseCounter >= 0) && bi->loopPredValid) {
pred_taken = bi->loopPred;
+ bi->provider = LOOP;
}
DPRINTF(LTage, "Predict for %lx: taken?:%d, loopTaken?:%d, "
"loopValid?:%d, loopUseCounter:%d, tagePred:%d, altPred:%d\n",
@@ -288,6 +289,43 @@
TAGE::squash(tid, bp_history);
}
+
+void
+LTAGE::updateStats(bool taken, TageBranchInfo* bi)
+{
+ TAGE::updateStats(taken, bi);
+
+ LTageBranchInfo * ltage_bi = static_cast<LTageBranchInfo *>(bi);
+
+ if (ltage_bi->provider == LOOP) {
+ if (taken == ltage_bi->loopPred) {
+ loopPredictorCorrect++;
+ } else {
+ loopPredictorWrong++;
+ }
+ }
+}
+
+
+
+void
+LTAGE::regStats()
+{
+ TAGE::regStats();
+
+ loopPredictorCorrect
+ .name(name() + ".loopPredictorCorrect")
+ .desc("Number of times the loop predictor is the provider and "
+ "the prediction is correct");
+
+ loopPredictorWrong
+ .name(name() + ".loopPredictorWrong")
+ .desc("Number of times the loop predictor is the provier and "
+ "the prediction is wrong");
+}
+
+
+
LTAGE*
LTAGEParams::create()
{
diff --git a/src/cpu/pred/ltage.hh b/src/cpu/pred/ltage.hh
index d614026..e9e34b7 100644
--- a/src/cpu/pred/ltage.hh
+++ b/src/cpu/pred/ltage.hh
@@ -67,6 +67,8 @@
// Base class methods.
void squash(ThreadID tid, void *bp_history) override;
+ void regStats() override;
+
private:
// Prediction Structures
// Loop Predictor Entry
@@ -84,6 +86,11 @@
confidence(0), tag(0), age(0), dir(0) { }
};
+ // more provider types
+ enum {
+ LOOP = LAST_TAGE_PROVIDER_TYPE + 1
+ };
+
// Primary branch history entry
struct LTageBranchInfo : public TageBranchInfo
{
@@ -177,6 +184,14 @@
void squash(
ThreadID tid, bool taken, void *bp_history) override;
+ /**
+ * Update the stats
+ * @param taken Actual branch outcome
+ * @param bi Pointer to information on the prediction
+ * recorded at prediction time.
+ */
+ void updateStats(bool taken, TageBranchInfo* bi) override;
+
const unsigned logSizeLoopPred;
const unsigned loopTableAgeBits;
const unsigned loopTableConfidenceBits;
@@ -191,6 +206,10 @@
int8_t loopUseCounter;
unsigned withLoopBits;
+
+ // stats
+ Stats::Scalar loopPredictorCorrect;
+ Stats::Scalar loopPredictorWrong;
};
#endif // __CPU_PRED_LTAGE
diff --git a/src/cpu/pred/tage.cc b/src/cpu/pred/tage.cc
index c22e6b7..061f808 100644
--- a/src/cpu/pred/tage.cc
+++ b/src/cpu/pred/tage.cc
@@ -348,16 +348,19 @@
//if the entry is recognized as a newly allocated entry and
//useAltPredForNewlyAllocated is positive use the alternate
//prediction
- if ((useAltPredForNewlyAllocated < 0)
- || abs(2 *
- gtable[bi->hitBank][tableIndices[bi->hitBank]].ctr + 1) > 1)
+ if ((useAltPredForNewlyAllocated < 0) || ! bi->pseudoNewAlloc) {
bi->tagePred = bi->longestMatchPred;
- else
+ bi->provider = TAGE_LONGEST_MATCH;
+ } else {
bi->tagePred = bi->altTaken;
+ bi->provider = bi->altBank ? TAGE_ALT_MATCH
+ : BIMODAL_ALT_MATCH;
+ }
} else {
bi->altTaken = getBimodePred(pc, bi);
bi->tagePred = bi->altTaken;
bi->longestMatchPred = bi->altTaken;
+ bi->provider = BIMODAL_ONLY;
}
//end TAGE prediction
@@ -390,6 +393,7 @@
if (bi->condBranch) {
DPRINTF(Tage, "Updating tables for branch:%lx; taken?:%d\n",
branch_pc, taken);
+ updateStats(taken, bi);
condBranchUpdate(branch_pc, taken, bi, nrand);
}
if (!squashed) {
@@ -602,6 +606,119 @@
&threadHistory[tid].globalHistory[threadHistory[tid].ptGhist]);
}
+void
+TAGE::updateStats(bool taken, TageBranchInfo* bi)
+{
+ if (taken == bi->tagePred) {
+ // correct prediction
+ switch (bi->provider) {
+ case BIMODAL_ONLY: tageBimodalProviderCorrect++; break;
+ case TAGE_LONGEST_MATCH: tageLongestMatchProviderCorrect++; break;
+ case BIMODAL_ALT_MATCH: bimodalAltMatchProviderCorrect++; break;
+ case TAGE_ALT_MATCH: tageAltMatchProviderCorrect++; break;
+ }
+ } else {
+ // wrong prediction
+ switch (bi->provider) {
+ case BIMODAL_ONLY: tageBimodalProviderWrong++; break;
+ case TAGE_LONGEST_MATCH:
+ tageLongestMatchProviderWrong++;
+ if (bi->altTaken == taken) {
+ tageAltMatchProviderWouldHaveHit++;
+ }
+ break;
+ case BIMODAL_ALT_MATCH:
+ bimodalAltMatchProviderWrong++;
+ break;
+ case TAGE_ALT_MATCH:
+ tageAltMatchProviderWrong++;
+ break;
+ }
+
+ switch (bi->provider) {
+ case BIMODAL_ALT_MATCH:
+ case TAGE_ALT_MATCH:
+ if (bi->longestMatchPred == taken) {
+ tageLongestMatchProviderWouldHaveHit++;
+ }
+ }
+ }
+
+ switch (bi->provider) {
+ case TAGE_LONGEST_MATCH:
+ case TAGE_ALT_MATCH:
+ tageLongestMatchProvider[bi->hitBank]++;
+ tageAltMatchProvider[bi->altBank]++;
+ break;
+ }
+}
+
+void
+TAGE::regStats()
+{
+ BPredUnit::regStats();
+
+ tageLongestMatchProviderCorrect
+ .name(name() + ".tageLongestMatchProviderCorrect")
+ .desc("Number of times TAGE Longest Match is the provider and "
+ "the prediction is correct");
+
+ tageAltMatchProviderCorrect
+ .name(name() + ".tageAltMatchProviderCorrect")
+ .desc("Number of times TAGE Alt Match is the provider and "
+ "the prediction is correct");
+
+ bimodalAltMatchProviderCorrect
+ .name(name() + ".bimodalAltMatchProviderCorrect")
+ .desc("Number of times TAGE Alt Match is the bimodal and it is the "
+ "provider and the prediction is correct");
+
+ tageBimodalProviderCorrect
+ .name(name() + ".tageBimodalProviderCorrect")
+ .desc("Number of times there are no hits on the TAGE tables "
+ "and the bimodal prediction is correct");
+
+ tageLongestMatchProviderWrong
+ .name(name() + ".tageLongestMatchProviderWrong")
+ .desc("Number of times TAGE Longest Match is the provider and "
+ "the prediction is wrong");
+
+ tageAltMatchProviderWrong
+ .name(name() + ".tageAltMatchProviderWrong")
+ .desc("Number of times TAGE Alt Match is the provider and "
+ "the prediction is wrong");
+
+ bimodalAltMatchProviderWrong
+ .name(name() + ".bimodalAltMatchProviderWrong")
+ .desc("Number of times TAGE Alt Match is the bimodal and it is the "
+ "provider and the prediction is wrong");
+
+ tageBimodalProviderWrong
+ .name(name() + ".tageBimodalProviderWrong")
+ .desc("Number of times there are no hits on the TAGE tables "
+ "and the bimodal prediction is wrong");
+
+ tageAltMatchProviderWouldHaveHit
+ .name(name() + ".tageAltMatchProviderWouldHaveHit")
+ .desc("Number of times TAGE Longest Match is the provider, "
+ "the prediction is wrong and Alt Match prediction was correct");
+
+ tageLongestMatchProviderWouldHaveHit
+ .name(name() + ".tageLongestMatchProviderWouldHaveHit")
+ .desc("Number of times TAGE Alt Match is the provider, the "
+ "prediction is wrong and Longest Match prediction was correct");
+
+ tageLongestMatchProvider
+ .init(nHistoryTables + 1)
+ .name(name() + ".tageLongestMatchProvider")
+ .desc("TAGE provider for longest match");
+
+ tageAltMatchProvider
+ .init(nHistoryTables + 1)
+ .name(name() + ".tageAltMatchProvider")
+ .desc("TAGE provider for alt match");
+}
+
TAGE*
TAGEParams::create()
{
diff --git a/src/cpu/pred/tage.hh b/src/cpu/pred/tage.hh
index 9ba0241..c66c28c 100644
--- a/src/cpu/pred/tage.hh
+++ b/src/cpu/pred/tage.hh
@@ -71,6 +71,8 @@
virtual void squash(ThreadID tid, void *bp_history) override;
unsigned getGHR(ThreadID tid, void *bp_history) const override;
+ virtual void regStats() override;
+
protected:
// Prediction Structures
@@ -110,6 +112,15 @@
}
};
+ // provider type
+ enum {
+ BIMODAL_ONLY = 0,
+ TAGE_LONGEST_MATCH,
+ BIMODAL_ALT_MATCH,
+ TAGE_ALT_MATCH,
+ LAST_TAGE_PROVIDER_TYPE = TAGE_ALT_MATCH
+ };
+
// Primary branch history entry
struct TageBranchInfo
{
@@ -141,6 +152,9 @@
int *ct0;
int *ct1;
+ // for stats purposes
+ unsigned provider;
+
TageBranchInfo(int sz)
: pathHist(0), ptGhist(0),
hitBank(0), hitBankIndex(0),
@@ -148,7 +162,8 @@
bimodalIndex(0),
tagePred(false), altTaken(false),
condBranch(false), longestMatchPred(false),
- pseudoNewAlloc(false), branchPC(0)
+ pseudoNewAlloc(false), branchPC(0),
+ provider(-1)
{
storage = new int [sz * 5];
tableIndices = storage;
@@ -320,6 +335,14 @@
bool tagePredict(
ThreadID tid, Addr branch_pc, bool cond_branch, TageBranchInfo* bi);
+ /**
+ * Update the stats
+ * @param taken Actual branch outcome
+ * @param bi Pointer to information on the prediction
+ * recorded at prediction time.
+ */
+ virtual void updateStats(bool taken, TageBranchInfo* bi);
+
const unsigned logRatioBiModalHystEntries;
const unsigned nHistoryTables;
const unsigned tagTableCounterBits;
@@ -369,6 +392,21 @@
uint64_t tCounter;
uint64_t logUResetPeriod;
unsigned useAltOnNaBits;
+
+ // stats
+ Stats::Scalar tageLongestMatchProviderCorrect;
+ Stats::Scalar tageAltMatchProviderCorrect;
+ Stats::Scalar bimodalAltMatchProviderCorrect;
+ Stats::Scalar tageBimodalProviderCorrect;
+ Stats::Scalar tageLongestMatchProviderWrong;
+ Stats::Scalar tageAltMatchProviderWrong;
+ Stats::Scalar bimodalAltMatchProviderWrong;
+ Stats::Scalar tageBimodalProviderWrong;
+ Stats::Scalar tageAltMatchProviderWouldHaveHit;
+ Stats::Scalar tageLongestMatchProviderWouldHaveHit;
+
+ Stats::Vector tageLongestMatchProvider;
+ Stats::Vector tageAltMatchProvider;
};
#endif // __CPU_PRED_TAGE
