[fuchsia] Avoid unnecessary zx_clock_get(ZX_CLOCK_THREAD, ...) calls

When system tracing is enabled on the Fuchsia platform, avoid calling
|OS::GetCurrentThreadCPUMicros|.  The thread timestamp values are
discarded later, so querying them is wasteful w.r.t. both time and
trace buffer space.

Change-Id: I400075c89e69ddde6b032808859826c95f029008
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149395
Reviewed-by: Siva Annamalai <asiva@google.com>
Auto-Submit: Nathan Rogers <nathanrogers@google.com>
Commit-Queue: Siva Annamalai <asiva@google.com>

runtime/vm/os.h

@@ -63,6 +63,11 @@ class OS {
   // NOTE: This function will return -1 on OSs that are not supported.
   static int64_t GetCurrentThreadCPUMicros();
 
+  // If the tracing/timeline configuration on the current OS supports thread
+  // timestamps, returns the same value as |GetCurrentThreadCPUMicros|.
+  // Otherwise, returns -1.
+  static int64_t GetCurrentThreadCPUMicrosForTimeline();
+
   // Returns the activation frame alignment constraint or one if
   // the platform doesn't care. Guaranteed to be a power of two.
   static intptr_t ActivationFrameAlignment();

runtime/vm/os_android.cc

@@ -177,6 +177,10 @@ int64_t OS::GetCurrentThreadCPUMicros() {
   return result;
 }
 
+int64_t OS::GetCurrentThreadCPUMicrosForTimeline() {
+  return OS::GetCurrentThreadCPUMicros();
+}
+
 // TODO(5411554):  May need to hoist these architecture dependent code
 // into a architecture specific file e.g: os_ia32_linux.cc
 intptr_t OS::ActivationFrameAlignment() {

runtime/vm/os_fuchsia.cc

@@ -287,6 +287,13 @@ int64_t OS::GetCurrentThreadCPUMicros() {
   return now / kNanosecondsPerMicrosecond;
 }
 
+// On Fuchsia, thread timestamp values are not used in the tracing/timeline
+// integration. Because of this, we try to avoid querying them, since doing so
+// has both a runtime and trace buffer storage cost.
+int64_t OS::GetCurrentThreadCPUMicrosForTimeline() {
+  return -1;
+}
+
 // TODO(5411554):  May need to hoist these architecture dependent code
 // into a architecture specific file e.g: os_ia32_fuchsia.cc
 intptr_t OS::ActivationFrameAlignment() {

runtime/vm/os_linux.cc

@@ -492,6 +492,10 @@ int64_t OS::GetCurrentThreadCPUMicros() {
   return result;
 }
 
+int64_t OS::GetCurrentThreadCPUMicrosForTimeline() {
+  return OS::GetCurrentThreadCPUMicros();
+}
+
 // TODO(5411554):  May need to hoist these architecture dependent code
 // into a architecture specific file e.g: os_ia32_linux.cc
 intptr_t OS::ActivationFrameAlignment() {

runtime/vm/os_macos.cc

@@ -127,6 +127,10 @@ int64_t OS::GetCurrentThreadCPUMicros() {
 #endif
 }
 
+int64_t OS::GetCurrentThreadCPUMicrosForTimeline() {
+  return OS::GetCurrentThreadCPUMicros();
+}
+
 intptr_t OS::ActivationFrameAlignment() {
 #if HOST_OS_IOS
 #if TARGET_ARCH_ARM

runtime/vm/os_win.cc

@@ -174,6 +174,10 @@ int64_t OS::GetCurrentThreadCPUMicros() {
   return -1;
 }
 
+int64_t OS::GetCurrentThreadCPUMicrosForTimeline() {
+  return OS::GetCurrentThreadCPUMicros();
+}
+
 intptr_t OS::ActivationFrameAlignment() {
 #if defined(TARGET_ARCH_ARM64)
   return 16;

runtime/vm/timeline.cc

@@ -1581,7 +1581,7 @@ void DartTimelineEventHelpers::ReportTaskEvent(Thread* thread,
          (phase[0] == 'B') || (phase[0] == 'E'));
   ASSERT(phase[1] == '\0');
   const int64_t start = OS::GetCurrentMonotonicMicros();
-  const int64_t start_cpu = OS::GetCurrentThreadCPUMicros();
+  const int64_t start_cpu = OS::GetCurrentThreadCPUMicrosForTimeline();
   switch (phase[0]) {
     case 'n':
       event->AsyncInstant(name, id, start);

runtime/vm/timeline.h

@@ -248,11 +248,13 @@ class TimelineEvent {
                 int64_t async_id,
                 int64_t micros = OS::GetCurrentMonotonicMicros());
 
-  void DurationBegin(const char* label,
-                     int64_t micros = OS::GetCurrentMonotonicMicros(),
-                     int64_t thread_micros = OS::GetCurrentThreadCPUMicros());
-  void DurationEnd(int64_t micros = OS::GetCurrentMonotonicMicros(),
-                   int64_t thread_micros = OS::GetCurrentThreadCPUMicros());
+  void DurationBegin(
+      const char* label,
+      int64_t micros = OS::GetCurrentMonotonicMicros(),
+      int64_t thread_micros = OS::GetCurrentThreadCPUMicrosForTimeline());
+  void DurationEnd(
+      int64_t micros = OS::GetCurrentMonotonicMicros(),
+      int64_t thread_micros = OS::GetCurrentThreadCPUMicrosForTimeline());
 
   void Instant(const char* label,
                int64_t micros = OS::GetCurrentMonotonicMicros());
@@ -263,13 +265,14 @@ class TimelineEvent {
                 int64_t thread_start_micros = -1,
                 int64_t thread_end_micros = -1);
 
-  void Begin(const char* label,
-             int64_t micros = OS::GetCurrentMonotonicMicros(),
-             int64_t thread_micros = OS::GetCurrentThreadCPUMicros());
+  void Begin(
+      const char* label,
+      int64_t micros = OS::GetCurrentMonotonicMicros(),
+      int64_t thread_micros = OS::GetCurrentThreadCPUMicrosForTimeline());
 
   void End(const char* label,
            int64_t micros = OS::GetCurrentMonotonicMicros(),
-           int64_t thread_micros = OS::GetCurrentThreadCPUMicros());
+           int64_t thread_micros = OS::GetCurrentThreadCPUMicrosForTimeline());
 
   void Counter(const char* label,
                int64_t micros = OS::GetCurrentMonotonicMicros());