[PATCH] D25775: [ThinLTO] Default backend threads to heavyweight_hardware_concurrency

[Teresa Johnson via llvm-commits]

tejohnson created this revision.
tejohnson added reviewers: mehdi_amini, pcc.
tejohnson added a subscriber: llvm-commits.

Changes default backend parallelism from thread::hardware_concurrency to
the new llvm::heavyweight_hardware_concurrency, which for X86 Linux
defaults to the number of physical cores (and will fall back to
thread::hardware_concurrency otherwise). This avoid oversubscribing
the physical cores using hyperthreading.


https://reviews.llvm.org/D25775

Files:
  lib/LTO/LTO.cpp
  lib/LTO/ThinLTOCodeGenerator.cpp
  tools/gold/gold-plugin.cpp
  tools/llvm-lto2/llvm-lto2.cpp


Index: tools/llvm-lto2/llvm-lto2.cpp
===================================================================
--- tools/llvm-lto2/llvm-lto2.cpp
+++ tools/llvm-lto2/llvm-lto2.cpp
@@ -20,6 +20,7 @@
 #include "llvm/LTO/LTO.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/TargetSelect.h"
+#include "llvm/Support/Threading.h"
 
 using namespace llvm;
 using namespace lto;
@@ -52,7 +53,7 @@
                                        "distributed backend case"));
 
 static cl::opt<int> Threads("-thinlto-threads",
-                            cl::init(thread::hardware_concurrency()));
+                            cl::init(llvm::heavyweight_hardware_concurrency()));
 
 static cl::list<std::string> SymbolResolutions(
     "r",
Index: tools/gold/gold-plugin.cpp
===================================================================
--- tools/gold/gold-plugin.cpp
+++ tools/gold/gold-plugin.cpp
@@ -118,8 +118,8 @@
   static unsigned OptLevel = 2;
   // Default parallelism of 0 used to indicate that user did not specify.
   // Actual parallelism default value depends on implementation.
-  // Currently only affects ThinLTO, where the default is the
-  // hardware_concurrency.
+  // Currently only affects ThinLTO, where the default is
+  // llvm::heavyweight_hardware_concurrency.
   static unsigned Parallelism = 0;
   // Default regular LTO codegen parallelism (number of partitions).
   static unsigned ParallelCodeGenParallelismLevel = 1;
Index: lib/LTO/ThinLTOCodeGenerator.cpp
===================================================================
--- lib/LTO/ThinLTOCodeGenerator.cpp
+++ lib/LTO/ThinLTOCodeGenerator.cpp
@@ -43,6 +43,7 @@
 #include "llvm/Support/SHA1.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/ThreadPool.h"
+#include "llvm/Support/Threading.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Transforms/IPO.h"
 #include "llvm/Transforms/IPO/FunctionImport.h"
@@ -64,8 +65,8 @@
 
 namespace {
 
-static cl::opt<int> ThreadCount("threads",
-                                cl::init(std::thread::hardware_concurrency()));
+static cl::opt<int>
+    ThreadCount("threads", cl::init(llvm::heavyweight_hardware_concurrency()));
 
 static void diagnosticHandler(const DiagnosticInfo &DI) {
   DiagnosticPrinterRawOStream DP(errs());
Index: lib/LTO/LTO.cpp
===================================================================
--- lib/LTO/LTO.cpp
+++ lib/LTO/LTO.cpp
@@ -29,6 +29,7 @@
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/ThreadPool.h"
+#include "llvm/Support/Threading.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"
 #include "llvm/Target/TargetOptions.h"
@@ -227,7 +228,8 @@
 
 LTO::ThinLTOState::ThinLTOState(ThinBackend Backend) : Backend(Backend) {
   if (!Backend)
-    this->Backend = createInProcessThinBackend(thread::hardware_concurrency());
+    this->Backend =
+        createInProcessThinBackend(llvm::heavyweight_hardware_concurrency());
 }
 
 LTO::LTO(Config Conf, ThinBackend Backend,


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