[lib/Fuzzer] guess the right number of workers if -jobs=N is given but -workers=M is not. Update the docs.

llvm-svn: 237163

4 files changed, 18 insertions, 1 deletions

diff --git a/llvm/lib/Fuzzer/FuzzerDriver.cpp b/llvm/lib/Fuzzer/FuzzerDriver.cpp
index 8e960c4f570..d1f6953a748 100644
--- a/llvm/lib/Fuzzer/FuzzerDriver.cpp
+++ b/llvm/lib/Fuzzer/FuzzerDriver.cpp
@@ -203,6 +203,12 @@ int FuzzerDriver(int argc, char **argv, UserCallback Callback) {
     return 0;
   }
 
+  if (Flags.jobs > 0 && Flags.workers == 0) {
+    Flags.workers = std::min(NumberOfCpuCores() / 2, Flags.jobs);
+    if (Flags.workers > 1)
+      std::cerr << "Running " << Flags.workers << " workers\n";
+  }
+
   if (Flags.workers > 0 && Flags.jobs > 0)
     return RunInMultipleProcesses(argc, argv, Flags.workers, Flags.jobs);
 
diff --git a/llvm/lib/Fuzzer/FuzzerFlags.def b/llvm/lib/Fuzzer/FuzzerFlags.def
index 25dffe452b8..4507fdadee7 100644
--- a/llvm/lib/Fuzzer/FuzzerFlags.def
+++ b/llvm/lib/Fuzzer/FuzzerFlags.def
@@ -44,7 +44,8 @@ FUZZER_FLAG_INT(jobs, 0, "Number of jobs to run. If jobs >= 1 we spawn"
                           " this number of jobs in separate worker processes"
                           " with stdout/stderr redirected to fuzz-JOB.log.")
 FUZZER_FLAG_INT(workers, 0,
-            "Number of simultaneous worker processes to run the jobs.")
+            "Number of simultaneous worker processes to run the jobs."
+            " If zero, \"min(jobs,NumberOfCpuCores()/2)\" is used.")
 FUZZER_FLAG_INT(reload, 1,
                 "Reload the main corpus periodically to get new units"
                 "discovered by other processes.")
diff --git a/llvm/lib/Fuzzer/FuzzerInternal.h b/llvm/lib/Fuzzer/FuzzerInternal.h
index 868668885b3..496b6db1650 100644
--- a/llvm/lib/Fuzzer/FuzzerInternal.h
+++ b/llvm/lib/Fuzzer/FuzzerInternal.h
@@ -44,6 +44,8 @@ std::string Hash(const Unit &U);
 void SetTimer(int Seconds);
 void PrintFileAsBase64(const std::string &Path);
 
+int NumberOfCpuCores();
+
 class Fuzzer {
  public:
   struct FuzzingOptions {
diff --git a/llvm/lib/Fuzzer/FuzzerUtil.cpp b/llvm/lib/Fuzzer/FuzzerUtil.cpp
index 3635f39a10d..dc7154ca385 100644
--- a/llvm/lib/Fuzzer/FuzzerUtil.cpp
+++ b/llvm/lib/Fuzzer/FuzzerUtil.cpp
@@ -61,4 +61,12 @@ void SetTimer(int Seconds) {
   assert(Res == 0);
 }
 
+int NumberOfCpuCores() {
+  FILE *F = popen("nproc", "r");
+  int N = 0;
+  fscanf(F, "%d", &N);
+  fclose(F);
+  return N;
+}
+
 }  // namespace fuzzer