Enable high resolution time for TimeTicks::Now on Windows Canary

Enable high resolution time for TimeTicks::Now on Windows Canary

This should be unnoticeable, except for improved resolution in places such as window.performance.now().

The feature is enabled if the user is running Canary channel or has manually specified the --enable-high-resolution-time flag. This will only work if the CPU has a non-stop TSC and isn't a broken Athlon processor. UMA data show this is a safe combination.

The flag is propagated to renderer processes so that they know to enable it too.

BUG=158234
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=222396

[James Simonsen, 2013-08-15 19:04:29]

Patch set 1 is the original patch I landed. You'd already reviewed that, but it
was reverted.

The only new code is in patch set 3. It fixes Sleep.

[James Simonsen, 2013-08-21 23:18:42]

Ping?

[James Simonsen, 2013-09-04 20:34:22]

Ping?

This is the only thing that's changed since last time:

--- a/base/threading/platform_thread_win.cc
+++ b/base/threading/platform_thread_win.cc
@@ -135,7 +135,12 @@ void PlatformThread::YieldCurrentThread() {
 
 // static
 void PlatformThread::Sleep(TimeDelta duration) {
-  ::Sleep(duration.InMillisecondsRoundedUp());
+  // When measured with a high resolution clock, Sleep() sometimes returns much
+  // too early. We may need to call it repeatedly to get the desired duration.
+  TimeTicks start = TimeTicks::Now();
+  TimeDelta elapsed;
+  while ((elapsed = TimeTicks::Now() - start) < duration)
+    ::Sleep((duration - elapsed).InMillisecondsRoundedUp());
 }

[darin (slow to review), 2013-09-05 07:29:22]

LGTM. Apologies, this fell off my radar.


On 2013/09/04 20:34:22, James Simonsen wrote:
> Ping?
> 
> This is the only thing that's changed since last time:
> 
> --- a/base/threading/platform_thread_win.cc
> +++ b/base/threading/platform_thread_win.cc
> @@ -135,7 +135,12 @@ void PlatformThread::YieldCurrentThread() {
>  
>  // static
>  void PlatformThread::Sleep(TimeDelta duration) {
> -  ::Sleep(duration.InMillisecondsRoundedUp());
> +  // When measured with a high resolution clock, Sleep() sometimes returns
much
> +  // too early. We may need to call it repeatedly to get the desired
duration.
> +  TimeTicks start = TimeTicks::Now();
> +  TimeDelta elapsed;
> +  while ((elapsed = TimeTicks::Now() - start) < duration)
> +    ::Sleep((duration - elapsed).InMillisecondsRoundedUp());
>  }

Not sure if it is worth it, but this eliminates one arithmetic operations
per loop iteration:

TimeTicks end = TimeTicks::Now() + duration;
TimeTicks now;
while ((now = TimeTicks::Now()) < end)
  ::Sleep((end - now).InMillisecondsRoundedUp());

[commit-bot: I haz the power, 2013-09-10 18:11:54]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/simonjam@chromium.org/23147002/19001

[commit-bot: I haz the power, 2013-09-10 22:03:47]

Retried try job too often on linux_aura for step(s) browser_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_aura...

[commit-bot: I haz the power, 2013-09-10 22:07:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/simonjam@chromium.org/23147002/19001

[commit-bot: I haz the power, 2013-09-10 23:36:10]

Change committed as 222396