[llvm-exegesis] Add debug option to print per-measurement values

[boomanaiden154]

This patch adds a debug option to print per measurement latency and validation counter values. This makes it easier to debug certain transient issues that can be hard to spot just using the summary view at the end.

I've hacked print statements into this part of the code base enough times for debugging various things that I think it makes sense to be a proper debug macro.

[llvmbot]

@llvm/pr-subscribers-tools-llvm-exegesis

Author: Aiden Grossman (boomanaiden154)

Changes

This patch adds a debug option to print per measurement latency and validation counter values. This makes it easier to debug certain transient issues that can be hard to spot just using the summary view at the end.

I've hacked print statements into this part of the code base enough times for debugging various things that I think it makes sense to be a proper debug macro.

---

Full diff: https://github.com/llvm/llvm-project/pull/81219.diff

3 Files Affected:

• (modified) llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp (+41-41)
• (modified) llvm/tools/llvm-exegesis/lib/BenchmarkResult.h (+3)
• (modified) llvm/tools/llvm-exegesis/lib/LatencyBenchmarkRunner.cpp (+9-3)

diff --git a/llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp b/llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp
index c193a8e5027713..0d6317f06054f7 100644
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkResult.cpp
@@ -193,51 +193,12 @@ template <> struct SequenceElementTraits<exegesis::BenchmarkMeasure> {
   static const bool flow = false;
 };
 
-const char *validationEventToString(exegesis::ValidationEvent VE) {
-  switch (VE) {
-  case exegesis::ValidationEvent::InstructionRetired:
-    return "instructions-retired";
-  case exegesis::ValidationEvent::L1DCacheLoadMiss:
-    return "l1d-cache-load-misses";
-  case exegesis::ValidationEvent::L1DCacheStoreMiss:
-    return "l1d-cache-store-misses";
-  case exegesis::ValidationEvent::L1ICacheLoadMiss:
-    return "l1i-cache-load-misses";
-  case exegesis::ValidationEvent::DataTLBLoadMiss:
-    return "data-tlb-load-misses";
-  case exegesis::ValidationEvent::DataTLBStoreMiss:
-    return "data-tlb-store-misses";
-  case exegesis::ValidationEvent::InstructionTLBLoadMiss:
-    return "instruction-tlb-load-misses";
-  }
-  llvm_unreachable("Unhandled exegesis::ValidationEvent enum");
-}
-
-Expected<exegesis::ValidationEvent> stringToValidationEvent(StringRef Input) {
-  if (Input == "instructions-retired")
-    return exegesis::ValidationEvent::InstructionRetired;
-  else if (Input == "l1d-cache-load-misses")
-    return exegesis::ValidationEvent::L1DCacheLoadMiss;
-  else if (Input == "l1d-cache-store-misses")
-    return exegesis::ValidationEvent::L1DCacheStoreMiss;
-  else if (Input == "l1i-cache-load-misses")
-    return exegesis::ValidationEvent::L1ICacheLoadMiss;
-  else if (Input == "data-tlb-load-misses")
-    return exegesis::ValidationEvent::DataTLBLoadMiss;
-  else if (Input == "data-tlb-store-misses")
-    return exegesis::ValidationEvent::DataTLBStoreMiss;
-  else if (Input == "instruction-tlb-load-misses")
-    return exegesis::ValidationEvent::InstructionTLBLoadMiss;
-  else
-    return make_error<StringError>("Invalid validation event string",
-                                   errc::invalid_argument);
-}
 
 template <>
 struct CustomMappingTraits<std::map<exegesis::ValidationEvent, int64_t>> {
   static void inputOne(IO &Io, StringRef KeyStr,
                        std::map<exegesis::ValidationEvent, int64_t> &VI) {
-    Expected<exegesis::ValidationEvent> Key = stringToValidationEvent(KeyStr);
+    Expected<exegesis::ValidationEvent> Key = exegesis::stringToValidationEvent(KeyStr);
     if (!Key) {
       Io.setError("Key is not a valid validation event");
       return;
@@ -247,7 +208,7 @@ struct CustomMappingTraits<std::map<exegesis::ValidationEvent, int64_t>> {
 
   static void output(IO &Io, std::map<exegesis::ValidationEvent, int64_t> &VI) {
     for (auto &IndividualVI : VI) {
-      Io.mapRequired(validationEventToString(IndividualVI.first),
+      Io.mapRequired(exegesis::validationEventToString(IndividualVI.first),
                      IndividualVI.second);
     }
   }
@@ -480,6 +441,45 @@ bool operator==(const BenchmarkMeasure &A, const BenchmarkMeasure &B) {
          std::tie(B.Key, B.PerInstructionValue, B.PerSnippetValue);
 }
 
+const char *validationEventToString(ValidationEvent VE) {
+  switch (VE) {
+  case exegesis::ValidationEvent::InstructionRetired:
+    return "instructions-retired";
+  case exegesis::ValidationEvent::L1DCacheLoadMiss:
+    return "l1d-cache-load-misses";
+  case exegesis::ValidationEvent::L1DCacheStoreMiss:
+    return "l1d-cache-store-misses";
+  case exegesis::ValidationEvent::L1ICacheLoadMiss:
+    return "l1i-cache-load-misses";
+  case exegesis::ValidationEvent::DataTLBLoadMiss:
+    return "data-tlb-load-misses";
+  case exegesis::ValidationEvent::DataTLBStoreMiss:
+    return "data-tlb-store-misses";
+  case exegesis::ValidationEvent::InstructionTLBLoadMiss:
+    return "instruction-tlb-load-misses";
+  }
+  llvm_unreachable("Unhandled exegesis::ValidationEvent enum");
+}
+
+Expected<ValidationEvent> stringToValidationEvent(StringRef Input) {
+  if (Input == "instructions-retired")
+    return exegesis::ValidationEvent::InstructionRetired;
+  else if (Input == "l1d-cache-load-misses")
+    return exegesis::ValidationEvent::L1DCacheLoadMiss;
+  else if (Input == "l1d-cache-store-misses")
+    return exegesis::ValidationEvent::L1DCacheStoreMiss;
+  else if (Input == "l1i-cache-load-misses")
+    return exegesis::ValidationEvent::L1ICacheLoadMiss;
+  else if (Input == "data-tlb-load-misses")
+    return exegesis::ValidationEvent::DataTLBLoadMiss;
+  else if (Input == "data-tlb-store-misses")
+    return exegesis::ValidationEvent::DataTLBStoreMiss;
+  else if (Input == "instruction-tlb-load-misses")
+    return exegesis::ValidationEvent::InstructionTLBLoadMiss;
+  else
+    return make_error<StringError>("Invalid validation event string",
+                                   errc::invalid_argument);
+}
 
 } // namespace exegesis
 } // namespace llvm
diff --git a/llvm/tools/llvm-exegesis/lib/BenchmarkResult.h b/llvm/tools/llvm-exegesis/lib/BenchmarkResult.h
index 43f03ff5413388..1f16314986000e 100644
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkResult.h
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkResult.h
@@ -42,6 +42,9 @@ enum ValidationEvent {
   InstructionTLBLoadMiss
 };
 
+const char *validationEventToString(exegesis::ValidationEvent VE);
+Expected<ValidationEvent> stringToValidationEvent(StringRef Input);
+
 enum class BenchmarkPhaseSelectorE {
   PrepareSnippet,
   PrepareAndAssembleSnippet,
diff --git a/llvm/tools/llvm-exegesis/lib/LatencyBenchmarkRunner.cpp b/llvm/tools/llvm-exegesis/lib/LatencyBenchmarkRunner.cpp
index 633740494e33e7..cb1cd426e995e7 100644
--- a/llvm/tools/llvm-exegesis/lib/LatencyBenchmarkRunner.cpp
+++ b/llvm/tools/llvm-exegesis/lib/LatencyBenchmarkRunner.cpp
@@ -15,6 +15,8 @@
 #include <algorithm>
 #include <cmath>
 
+#define DEBUG_TYPE "exegesis-latency-benchmarkrunner"
+
 namespace llvm {
 namespace exegesis {
 
@@ -91,9 +93,10 @@ Expected<std::vector<BenchmarkMeasure>> LatencyBenchmarkRunner::runMeasurements(
     if (!ExpectedCounterValues)
       return ExpectedCounterValues.takeError();
     ValuesCount = ExpectedCounterValues.get().size();
-    if (ValuesCount == 1)
+    if (ValuesCount == 1) {
+      LLVM_DEBUG(dbgs() << "Latency value: " << ExpectedCounterValues.get()[0] << "\n");
       AccumulatedValues.push_back(ExpectedCounterValues.get()[0]);
-    else {
+    } else {
       // We'll keep the reading with lowest variance (ie., most stable)
       double Variance = computeVariance(*ExpectedCounterValues);
       if (MinVariance > Variance) {
@@ -102,8 +105,11 @@ Expected<std::vector<BenchmarkMeasure>> LatencyBenchmarkRunner::runMeasurements(
       }
     }
 
-    for (size_t I = 0; I < ValCounterValues.size(); ++I)
+    for (size_t I = 0; I < ValCounterValues.size(); ++I) {
+      LLVM_DEBUG(dbgs() << validationEventToString(ValidationCounters[I])
+                        << ": " << IterationValCounterValues[I] << "\n");
       ValCounterValues[I] += IterationValCounterValues[I];
+    }
   }
 
   std::map<ValidationEvent, int64_t> ValidationInfo;

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