[PATCH] D25585: Add interface for querying physical hardware concurrency

[Teresa Johnson via llvm-commits]

tejohnson created this revision.
tejohnson added a reviewer: mehdi_amini.
tejohnson added a subscriber: llvm-commits.
Herald added subscribers: mgorny, beanz.

This will be used by ThinLTO to set the amount of backend
parallelism, which performs better when restricted to the number
of physical cores (on X86 at least, where getHostNumPhysicalCores is
currently defined). If not available this falls back to
thread::hardware_concurrency.

Note I didn't add to the thread class since that is a typedef to
std::thread where available.


https://reviews.llvm.org/D25585

Files:
  include/llvm/Support/Threading.h
  lib/Support/Threading.cpp
  unittests/Support/CMakeLists.txt
  unittests/Support/Threading.cpp


Index: unittests/Support/Threading.cpp
===================================================================
--- /dev/null
+++ unittests/Support/Threading.cpp
@@ -0,0 +1,25 @@
+//===- unittests/Threading.cpp - Thread tests -----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Threading.h"
+#include "llvm/Support/thread.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(Threading, PhysicalConcurrency) {
+  auto Num = hardware_physical_concurrency();
+  // Since Num is unsigned this will also catch us trying to
+  // return -1.
+  ASSERT_LE(Num, thread::hardware_concurrency());
+}
+
+} // end anon namespace
Index: unittests/Support/CMakeLists.txt
===================================================================
--- unittests/Support/CMakeLists.txt
+++ unittests/Support/CMakeLists.txt
@@ -40,6 +40,7 @@
   StringPool.cpp
   SwapByteOrderTest.cpp
   TargetParserTest.cpp
+  Threading.cpp
   ThreadLocalTest.cpp
   ThreadPool.cpp
   TimerTest.cpp
Index: lib/Support/Threading.cpp
===================================================================
--- lib/Support/Threading.cpp
+++ lib/Support/Threading.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Support/Threading.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/Atomic.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/Mutex.h"
 #include "llvm/Support/thread.h"
 #include <cassert>
@@ -116,3 +117,10 @@
 }
 
 #endif
+
+unsigned llvm::hardware_physical_concurrency() {
+  int NumPhysical = sys::getHostNumPhysicalCores();
+  if (NumPhysical == -1)
+    return thread::hardware_concurrency();
+  return NumPhysical;
+}
Index: include/llvm/Support/Threading.h
===================================================================
--- include/llvm/Support/Threading.h
+++ include/llvm/Support/Threading.h
@@ -115,6 +115,10 @@
     TsanHappensAfter(&flag);
 #endif
   }
+
+  /// Get the amount of currency based on physical cores, if available for the
+  /// host system, otherwise falls back to thread::hardware_concurrency().
+  unsigned hardware_physical_concurrency();
 }
 
 #endif


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