Re: Answers to some comments about frame synchronization

[Alexander Larsson <alexl redhat com>]

On fre, 2013-02-15 at 09:21 +0100, Alexander Larsson wrote:
> On tor, 2013-02-14 at 16:18 -0500, Owen Taylor wrote:
> > On Thu, 2013-02-14 at 15:35 -0500, Alexander Larsson wrote:
>
> > > I did a bunch of research on this, see the g_get_monitonic_time() win32
> > > implementation for it. I definately don't think we can just rely on QPC
> > > as is. Its not monotonic, it will drift over time and i believe over e.g.
> > > cpu sleeps. If we use it we should slave it to the lower precision clock
> > > in some kind of PLL (this is what firefox does). I just couldn't be
> > > bothered with the complexity last time...
> >
> > The Firefox bug linked to from the GLib comments is 5 years old, and
> > in following through to various links, all the problems people were
> > describing were with Windows XP. I'm not convinced that this is a
> > current problem. DwmGetCompositionTimingInfo() which is the primary
> > interface we might want to interact with uses QPC time, so my impression
> > is that Microsoft's view of QPC is that it gives you sane timestamps
> > along the lines of CLOCK_MONOTONIC on Linux, and not uninterpreted rdtsc
> > values.
>
> That might be true, although we still support XP. All the official MS
> docs on this are really unclear though, which is kinda strange.
>
> http://msdn.microsoft.com/en-us/windows/hardware/gg463266.aspx seems to
> have some details though. It talks a bout timer coalescing too, which we
> should perhaps make the g_timeout_add_seconds calls use.

Here are some other references:
http://www.belshe.com/2010/06/04/chrome-cranking-up-the-clock/
http://gamedev.stackexchange.com/questions/32183/high-resolution-timer-options-in-windows
http://stackoverflow.com/questions/5559985/handling-the-game-loop-with-os-timers