Add interface to system trace clock.

Add TimeTicks::NowFromSystemTraceTime to return the current system trace
event clock (falling back to TimeTicks::HighResNow when not supported).
On systems where the system trace clock is available this allows
system and chrome events to be stamped with a common clock (eliminating
post-processing time shift adjustment that can be hard).

BUG=chromium-os:27809
TEST=unit tests + collect trace data on chrome os w/ kernel that supports clock_gettime(CLOCK_SYSTEM_TRACE)

Change-Id: Ia6a500bd13a6f09c49052a1dd1421027960d8dea


Review URL: http://codereview.chromium.org/10257020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@134772 0039d316-1c4b-4281-b951-d872f2087c98

base/debug/trace_event_impl.cc

@@ -585,7 +585,7 @@ int TraceLog::AddTraceEvent(char phase,
                             long long threshold,
                             unsigned char flags) {
   DCHECK(name);
-  TimeTicks now = TimeTicks::HighResNow();
+  TimeTicks now = TimeTicks::NowFromSystemTraceTime();
   BufferFullCallback buffer_full_callback_copy;
   int ret_begin_id = -1;
   {
@@ -710,7 +710,7 @@ void TraceLog::AddClockSyncMetadataEvents() {
   // debugfs that takes the written data and pushes it onto the trace
   // buffer. So, to establish clock sync, we write our monotonic clock into that
   // trace buffer.
-  TimeTicks now = TimeTicks::HighResNow();
+  TimeTicks now = TimeTicks::NowFromSystemTraceTime();
 
   double now_in_seconds = now.ToInternalValue() / 1000000.0;
   std::string marker =

base/time.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -482,6 +482,13 @@ class BASE_EXPORT TimeTicks {
   // SHOULD ONLY BE USED WHEN IT IS REALLY NEEDED.
   static TimeTicks HighResNow();
 
+  // Returns the current system trace time or, if none is defined, the current
+  // high-res time (i.e. HighResNow()). On systems where a global trace clock
+  // is defined, timestamping TraceEvents's with this value guarantees
+  // synchronization between events collected inside chrome and events
+  // collected outside (e.g. kernel, X server).
+  static TimeTicks NowFromSystemTraceTime();
+
 #if defined(OS_WIN)
   // Get the absolute value of QPC time drift. For testing.
   static int64 GetQPCDriftMicroseconds();

base/time_mac.cc

@@ -148,4 +148,9 @@ TimeTicks TimeTicks::HighResNow() {
   return Now();
 }
 
+// static
+TimeTicks TimeTicks::NowFromSystemTraceTime() {
+  return HighResNow();
+}
+
 }  // namespace base

base/time_posix.cc

@@ -228,6 +228,34 @@ TimeTicks TimeTicks::HighResNow() {
   return Now();
 }
 
+#if defined(OS_POSIX) && defined(CLOCK_SYSTEM_TRACE)
+
+// static
+TimeTicks TimeTicks::NowFromSystemTraceTime() {
+  uint64_t absolute_micro;
+
+  struct timespec ts;
+  if (clock_gettime(CLOCK_SYSTEM_TRACE, &ts) != 0) {
+    NOTREACHED() << "clock_gettime(CLOCK_SYSTEM_TRACE) failed.";
+    return HighResNow();
+  }
+
+  absolute_micro =
+      (static_cast<int64>(ts.tv_sec) * Time::kMicrosecondsPerSecond) +
+      (static_cast<int64>(ts.tv_nsec) / Time::kNanosecondsPerMicrosecond);
+
+  return TimeTicks(absolute_micro);
+}
+
+#else // !(defined(OS_POSIX) && defined(CLOCK_SYSTEM_TRACE))
+
+// static
+TimeTicks TimeTicks::NowFromSystemTraceTime() {
+  return HighResNow();
+}
+
+#endif // defined(OS_POSIX) && defined(CLOCK_SYSTEM_TRACE)
+
 #endif  // !OS_MACOSX
 
 struct timeval Time::ToTimeVal() const {

base/time_unittest.cc

@@ -464,7 +464,7 @@ TEST(TimeTicks, Deltas) {
   }
 }
 
-TEST(TimeTicks, HighResNow) {
+static void HighResClockTest(TimeTicks (*GetTicks)()) {
 #if defined(OS_WIN)
   // HighResNow doesn't work on some systems.  Since the product still works
   // even if it doesn't work, it makes this entire test questionable.
@@ -486,12 +486,12 @@ TEST(TimeTicks, HighResNow) {
   int retries = 100;  // Arbitrary.
   TimeDelta delta;
   while (!success && retries--) {
-    TimeTicks ticks_start = TimeTicks::HighResNow();
+    TimeTicks ticks_start = GetTicks();
     // Loop until we can detect that the clock has changed.  Non-HighRes timers
     // will increment in chunks, e.g. 15ms.  By spinning until we see a clock
     // change, we detect the minimum time between measurements.
     do {
-      delta = TimeTicks::HighResNow() - ticks_start;
+      delta = GetTicks() - ticks_start;
     } while (delta.InMilliseconds() == 0);
 
     if (delta.InMicroseconds() <= kTargetGranularityUs)
@@ -503,6 +503,15 @@ TEST(TimeTicks, HighResNow) {
   EXPECT_TRUE(success);
 }
 
+TEST(TimeTicks, HighResNow) {
+  HighResClockTest(&TimeTicks::HighResNow);
+}
+
+TEST(TimeTicks, NowFromSystemTraceTime) {
+  // Re-use HighResNow test for now since clock properties are identical.
+  HighResClockTest(&TimeTicks::NowFromSystemTraceTime);
+}
+
 TEST(TimeDelta, FromAndIn) {
   EXPECT_TRUE(TimeDelta::FromDays(2) == TimeDelta::FromHours(48));
   EXPECT_TRUE(TimeDelta::FromHours(3) == TimeDelta::FromMinutes(180));

base/time_win.cc

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -435,6 +435,11 @@ TimeTicks TimeTicks::HighResNow() {
   return TimeTicks() + HighResNowSingleton::GetInstance()->Now();
 }
 
+// static
+TimeTicks TimeTicks::NowFromSystemTraceTime() {
+  return HighResNow();
+}
+
 // static
 int64 TimeTicks::GetQPCDriftMicroseconds() {
   return HighResNowSingleton::GetInstance()->GetQPCDriftMicroseconds();