Bring r314809 back.
But now include a check for CPU_COUNT so we still build on 10 year old
versions of glibc.
Original message:
Use sched_getaffinity instead of std::thread::hardware_concurrency.
The issue with std::thread::hardware_concurrency is that it forwards
to libc and some implementations (like glibc) don't take thread
affinity into consideration.
With this change a llvm program that can execute in only 2 cores will
use 2 threads, even if the machine has 32 cores.
This makes benchmarking a lot easier, but should also help if someone
doesn't want to use all cores for compilation for example.
llvm-svn: 314931
diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index 6a10b98..473c848 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/lib/Support/Threading.cpp
@@ -47,6 +47,8 @@
unsigned llvm::heavyweight_hardware_concurrency() { return 1; }
+unsigned llvm::hardware_concurrency() { return 1; }
+
uint64_t llvm::get_threadid() { return 0; }
uint32_t llvm::get_max_thread_name_length() { return 0; }
@@ -71,6 +73,18 @@
return NumPhysical;
}
+unsigned llvm::hardware_concurrency() {
+#if defined(HAVE_SCHED_GETAFFINITY) && defined(HAVE_CPU_COUNT)
+ cpu_set_t Set;
+ if (sched_getaffinity(0, sizeof(Set), &Set))
+ return CPU_COUNT(&Set);
+#endif
+ // Guard against std::thread::hardware_concurrency() returning 0.
+ if (unsigned Val = std::thread::hardware_concurrency())
+ return Val;
+ return 1;
+}
+
// Include the platform-specific parts of this class.
#ifdef LLVM_ON_UNIX
#include "Unix/Threading.inc"