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>

1 files changed, 121 insertions, 4 deletions

diff --git a/src/cpu/pred/tage.cc b/src/cpu/pred/tage.cc
index c22e6b7a5..061f808e8 100644
--- a/src/cpu/pred/tage.cc
+++ b/src/cpu/pred/tage.cc
@@ -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()
 {