[PATCH] D97504: [llvm-exegesis] Disable the LBR check on AMD

[Vy Nguyen via Phabricator via llvm-commits]

oontvoo created this revision.
oontvoo added reviewers: ondrasej, courbet.
Herald added a subscriber: mstojanovic.
oontvoo requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

https://bugs.llvm.org/show_bug.cgi?id=48918

The bug reported a hang (or very very slow runtime) on a Zen2. Unfortunately, we don't have the hardware right now to debug it and I was not able to reproduce the bug on a HSW.
Theory we've got is that the lbr-checking code could be confused on AMD.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97504

Files:
  llvm/tools/llvm-exegesis/lib/Target.h
  llvm/tools/llvm-exegesis/lib/X86/Target.cpp
  llvm/tools/llvm-exegesis/llvm-exegesis.cpp


Index: llvm/tools/llvm-exegesis/llvm-exegesis.cpp
===================================================================
--- llvm/tools/llvm-exegesis/llvm-exegesis.cpp
+++ llvm/tools/llvm-exegesis/llvm-exegesis.cpp
@@ -11,6 +11,8 @@
 ///
 //===----------------------------------------------------------------------===//
 
+#include <iostream>
+
 #include "lib/Analysis.h"
 #include "lib/BenchmarkResult.h"
 #include "lib/BenchmarkRunner.h"
@@ -297,9 +299,14 @@
 
   const LLVMState State(CpuName);
 
+  std::cout << State.getSubtargetInfo().getCPU().str();
+  //  std::cout << "*** CPU name = " <<  std::cout <<
+  //  State.getSubtargetInfo().getCPU().str()
+  //  State.getTargetMachine().getTargetFeatureString().str();
+
   // Preliminary check to ensure features needed for requested
   // benchmark mode are present on target CPU and/or OS.
-  ExitOnErr(State.getExegesisTarget().checkFeatureSupport());
+  ExitOnErr(State.getExegesisTarget().checkFeatureSupport(State));
 
   const std::unique_ptr<BenchmarkRunner> Runner =
       ExitOnErr(State.getExegesisTarget().createBenchmarkRunner(
Index: llvm/tools/llvm-exegesis/lib/X86/Target.cpp
===================================================================
--- llvm/tools/llvm-exegesis/lib/X86/Target.cpp
+++ llvm/tools/llvm-exegesis/lib/X86/Target.cpp
@@ -719,7 +719,7 @@
     return Arch == Triple::x86_64 || Arch == Triple::x86;
   }
 
-  Error checkFeatureSupport() const override {
+  Error checkFeatureSupport(const LLVMState &state) const override {
     // LBR is the only feature we conditionally support now.
     // So if LBR is not requested, then we should be able to run the benchmarks.
     if (LbrSamplingPeriod == 0)
@@ -727,13 +727,18 @@
 
 #if defined(__linux__) && defined(HAVE_LIBPFM) &&                              \
     defined(LIBPFM_HAS_FIELD_CYCLES)
-    // If the kernel supports it, the hardware still may not have it.
-    return X86LbrCounter::checkLbrSupport();
-#else
+    // FIXME: Fix this.
+    // https://bugs.llvm.org/show_bug.cgi?id=48918
+    // For now, don't do the check if we see an AMD machine because
+    // the counter uses some intel-specific magic and it could
+    // be confuse and think the AMD machine actually has LBR support.
+    if (state.getSubtargetInfo().getCPU().compare_lower("amd") != 0)
+      // If the kernel supports it, the hardware still may not have it.
+      return X86LbrCounter::checkLbrSupport();
+#endif
     return llvm::make_error<llvm::StringError>(
         "LBR not supported on this kernel and/or platform",
         llvm::errc::not_supported);
-#endif
   }
 
   std::unique_ptr<SavedState> withSavedState() const override {
Index: llvm/tools/llvm-exegesis/lib/Target.h
===================================================================
--- llvm/tools/llvm-exegesis/lib/Target.h
+++ llvm/tools/llvm-exegesis/lib/Target.h
@@ -145,7 +145,9 @@
   // Checks hardware and software support for current benchmark mode.
   // Returns an error if the target host does not have support to run the
   // benchmark.
-  virtual Error checkFeatureSupport() const { return Error::success(); }
+  virtual Error checkFeatureSupport(const LLVMState &) const {
+    return Error::success();
+  }
 
   // Creates a snippet generator for the given mode.
   std::unique_ptr<SnippetGenerator>


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