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cpu: Added new stats to TAGE and LTAGE branch predictors

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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>
This commit is contained in:
Pau Cabre
2018-11-22 14:48:30 +01:00
parent b2078cef37
commit 86b23a175c
4 changed files with 217 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

38
src/cpu/pred/ltage.cc
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@@ -228,6 +228,7 @@ LTAGE::predict(ThreadID tid, Addr branch_pc, bool cond_branch, void* &b)
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 @@ LTAGE::squash(ThreadID tid, void *bp_history)
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()
{

19
src/cpu/pred/ltage.hh
View File

@@ -67,6 +67,8 @@ class LTAGE: public TAGE
// Base class methods.
void squash(ThreadID tid, void *bp_history) override;
void regStats() override;
private:
// Prediction Structures
// Loop Predictor Entry
@@ -84,6 +86,11 @@ class LTAGE: public TAGE
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 @@ class LTAGE: public TAGE
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 @@ class LTAGE: public TAGE
int8_t loopUseCounter;
unsigned withLoopBits;
// stats
Stats::Scalar loopPredictorCorrect;
Stats::Scalar loopPredictorWrong;
};
#endif // __CPU_PRED_LTAGE

125
src/cpu/pred/tage.cc
View File

@@ -348,16 +348,19 @@ TAGE::tagePredict(ThreadID tid, Addr branch_pc,
//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 @@ TAGE::update(ThreadID tid, Addr branch_pc, bool taken, void* bp_history,
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 @@ TAGE::uncondBranch(ThreadID tid, Addr br_pc, void* &bp_history)
&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()
{

40
src/cpu/pred/tage.hh
View File

@@ -71,6 +71,8 @@ class TAGE: public BPredUnit
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 @@ class TAGE: public BPredUnit
}
};
// 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 @@ class TAGE: public BPredUnit
int *ct0;
int *ct1;
// for stats purposes
unsigned provider;
TageBranchInfo(int sz)
: pathHist(0), ptGhist(0),
hitBank(0), hitBankIndex(0),
@@ -148,7 +162,8 @@ class TAGE: public BPredUnit
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 @@ class TAGE: public BPredUnit
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 @@ class TAGE: public BPredUnit
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