[PATCH] D47572: [llvm-exegesis][NFCI] Counter::Counter(): more useful msg on even open error

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: courbet, RKSimon.
Herald added a subscriber: tschuett.

I'm slowly looking into a new X86 scheduler model,
for AMD Bulldozer CPU, model 2 (bdver2, Piledriver).

And naturally, i have hit that assert :)
I happened to know what it meant, and how to fix it,
but that is not too common knowledge.


Repository:
  rL LLVM

https://reviews.llvm.org/D47572

Files:
  tools/llvm-exegesis/lib/PerfHelper.cpp


Index: tools/llvm-exegesis/lib/PerfHelper.cpp
===================================================================
--- tools/llvm-exegesis/lib/PerfHelper.cpp
+++ tools/llvm-exegesis/lib/PerfHelper.cpp
@@ -96,9 +96,13 @@
   const uint32_t Flags = 0;
   perf_event_attr AttrCopy = *Event.attribute();
   FileDescriptor = perf_event_open(&AttrCopy, Pid, Cpu, GroupFd, Flags);
-  assert(FileDescriptor != -1 &&
-         "Unable to open event, make sure your kernel allows user space perf "
-         "monitoring.");
+  if (FileDescriptor == -1) {
+    llvm::errs()
+        << "Unable to open event, make sure your kernel allows user space perf "
+           "monitoring.\nYou may want to try:\n$ sudo sh -c 'echo -1 "
+           ">/proc/sys/kernel/perf_event_paranoid'\n";
+  }
+  assert(FileDescriptor != -1 && "Unable to open event");
 }
 
 Counter::~Counter() { close(FileDescriptor); }


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