commit 5494e5b2e6fde8f86110173a1a13daa035f987ae
author Mathieu Chartier <mathieuc@google.com> Mon Jun 26 14:13:27 2017 -0700
committer Mathieu Chartier <mathieuc@google.com> Tue Jun 27 15:21:03 2017 -0700
tree 411d1a264056371ff32b2abd31ee6e6d6c6a6c49
parent 9d7fd996bb79d28c86ae4e31e0f3c05c779e27dd

Restore profile saver priority in GC critical section

Restore profile saver thread priority during the GC critical section.
This helps prevent priority inversions blocking the GC for long
periods of time.

Average time spent in GC critical section during phone booting
(20 samples): 137.4963182ms -> 62.22603846ms

Bug: 62941975
Test: phone boot and make

Change-Id: Ie8180974e92a7bf5ebb847eeee741c7fd5bdf59f

runtime/jit/profile_saver.cc

diff --git a/runtime/jit/profile_saver.cc b/runtime/jit/profile_saver.cc
index b41bc78..10dddae 100644
--- a/runtime/jit/profile_saver.cc
+++ b/runtime/jit/profile_saver.cc
@@ -43,6 +43,33 @@
 ProfileSaver* ProfileSaver::instance_ = nullptr;
 pthread_t ProfileSaver::profiler_pthread_ = 0U;
 
+// At what priority to schedule the saver threads. 9 is the lowest foreground priority on device.
+static constexpr int kProfileSaverPthreadPriority = 9;
+
+static void SetProfileSaverThreadPriority(pthread_t thread, int priority) {
+#if defined(ART_TARGET_ANDROID)
+  int result = setpriority(PRIO_PROCESS, pthread_gettid_np(thread), priority);
+  if (result != 0) {
+    LOG(ERROR) << "Failed to setpriority to :" << priority;
+  }
+#else
+  UNUSED(thread);
+  UNUSED(priority);
+#endif
+}
+
+static int GetDefaultThreadPriority() {
+#if defined(ART_TARGET_ANDROID)
+  pthread_attr_t attr;
+  sched_param param;
+  pthread_attr_init(&attr);
+  pthread_attr_getschedparam(&attr, &param);
+  return param.sched_priority;
+#else
+  return 0;
+#endif
+}
+
 ProfileSaver::ProfileSaver(const ProfileSaverOptions& options,
                            const std::string& output_filename,
                            jit::JitCodeCache* jit_code_cache,
@@ -241,6 +268,20 @@
   const bool profile_boot_class_path_;
 };
 
+class ScopedDefaultPriority {
+ public:
+  explicit ScopedDefaultPriority(pthread_t thread) : thread_(thread) {
+    SetProfileSaverThreadPriority(thread_, GetDefaultThreadPriority());
+  }
+
+  ~ScopedDefaultPriority() {
+    SetProfileSaverThreadPriority(thread_, kProfileSaverPthreadPriority);
+  }
+
+ private:
+  const pthread_t thread_;
+};
+
 void ProfileSaver::FetchAndCacheResolvedClassesAndMethods() {
   ScopedTrace trace(__PRETTY_FUNCTION__);
   const uint64_t start_time = NanoTime();
@@ -257,7 +298,15 @@
   TypeReferenceCollection resolved_classes(allocator.Adapter(), allocator.Adapter());
   const bool is_low_ram = Runtime::Current()->GetHeap()->IsLowMemoryMode();
   const size_t hot_threshold = options_.GetHotStartupMethodSamples(is_low_ram);
+  pthread_t profiler_pthread;
   {
+    MutexLock mu(self, *Locks::profiler_lock_);
+    profiler_pthread = profiler_pthread_;
+  }
+  {
+    // Restore profile saver thread priority during the GC critical section. This helps prevent
+    // priority inversions blocking the GC for long periods of time.
+    ScopedDefaultPriority sdp(profiler_pthread);
     ScopedObjectAccess soa(self);
     gc::ScopedGCCriticalSection sgcs(self,
                                      gc::kGcCauseProfileSaver,
@@ -543,15 +592,7 @@
       (&profiler_pthread_, nullptr, &RunProfileSaverThread, reinterpret_cast<void*>(instance_)),
       "Profile saver thread");
 
-#if defined(ART_TARGET_ANDROID)
-  // At what priority to schedule the saver threads. 9 is the lowest foreground priority on device.
-  static constexpr int kProfileSaverPthreadPriority = 9;
-  int result = setpriority(
-      PRIO_PROCESS, pthread_gettid_np(profiler_pthread_), kProfileSaverPthreadPriority);
-  if (result != 0) {
-    PLOG(ERROR) << "Failed to setpriority to :" << kProfileSaverPthreadPriority;
-  }
-#endif
+  SetProfileSaverThreadPriority(profiler_pthread_, kProfileSaverPthreadPriority);
 }
 
 void ProfileSaver::Stop(bool dump_info) {