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

3 files changed, 19 insertions, 4 deletions

diff --git a/llvm/lib/Support/Parallel.cpp b/llvm/lib/Support/Parallel.cpp
index ab2cfdebf07..010e42916f9 100644
--- a/llvm/lib/Support/Parallel.cpp
+++ b/llvm/lib/Support/Parallel.cpp
@@ -9,6 +9,7 @@
 
 #include "llvm/Support/Parallel.h"
 #include "llvm/Config/llvm-config.h"
+#include "llvm/Support/Threading.h"
 
 #include <atomic>
 #include <stack>
@@ -70,8 +71,7 @@ Executor *Executor::getDefaultExecutor() {
 ///   in filo order.
 class ThreadPoolExecutor : public Executor {
 public:
-  explicit ThreadPoolExecutor(
-      unsigned ThreadCount = std::thread::hardware_concurrency())
+  explicit ThreadPoolExecutor(unsigned ThreadCount = hardware_concurrency())
       : Done(ThreadCount) {
     // Spawn all but one of the threads in another thread as spawning threads
     // can take a while.
diff --git a/llvm/lib/Support/ThreadPool.cpp b/llvm/lib/Support/ThreadPool.cpp
index 22b7550d497..f1b5bdf40c3 100644
--- a/llvm/lib/Support/ThreadPool.cpp
+++ b/llvm/lib/Support/ThreadPool.cpp
@@ -14,14 +14,15 @@
 #include "llvm/Support/ThreadPool.h"
 
 #include "llvm/Config/llvm-config.h"
+#include "llvm/Support/Threading.h"
 #include "llvm/Support/raw_ostream.h"
 
 using namespace llvm;
 
 #if LLVM_ENABLE_THREADS
 
-// Default to std::thread::hardware_concurrency
-ThreadPool::ThreadPool() : ThreadPool(std::thread::hardware_concurrency()) {}
+// Default to hardware_concurrency
+ThreadPool::ThreadPool() : ThreadPool(hardware_concurrency()) {}
 
 ThreadPool::ThreadPool(unsigned ThreadCount)
     : ActiveThreads(0), EnableFlag(true) {
diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index 6a10b988d46..473c84808af 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/lib/Support/Threading.cpp
@@ -47,6 +47,8 @@ void llvm::llvm_execute_on_thread(void (*Fn)(void *), void *UserData,
 
 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 @@ unsigned llvm::heavyweight_hardware_concurrency() {
   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"