[Mesa-dev] [PATCH 4/7] mesa: implement glGet(GL_TIMESTAMP)

[Marek Olšák]

On Wed, Jun 27, 2012 at 4:42 PM, Adam Jackson <ajax at redhat.com> wrote:
> On Wed, 2012-06-27 at 09:29 +0200, Michel Dänzer wrote:
>> On Mit, 2012-06-27 at 03:49 +0200, Marek Olšák wrote:
>> >
>> > +GLuint64
>> > +_mesa_get_cpu_timestamp(void)
>> > +{
>> > +#ifndef _WIN32
>> > +   struct timeval tv;
>> > +
>> > +   gettimeofday(&tv, 0);
>> > +   return (GLuint64)tv.tv_sec * 1000000000ull + (GLuint64)tv.tv_usec * 1000;
>>
>> As in a recent discussion about DRM vblank counters, it may be better to
>> use clock_gettime(CLOCK_MONOTONIC, ...) when possible, as gettimeofday()
>> can move backwards.
>
> And if you do so, since it looks like you're working in milliseconds,
> please steal xserver's GetTimeInMillis() for it:
>
> http://cgit.freedesktop.org/xorg/xserver/tree/os/utils.c#n409
> http://cgit.freedesktop.org/xorg/xserver/commit/os/utils.c?id=44adb31bfece29260a9bbd9075c9212ebf00d24d

I am working in nanoseconds and precision is quite important. I don't
think I can use CLOCK_MONOTONIC_COARSE. CLOCK_MONOTONIC might be fine.

Marek