[Intel-gfx] [RFC 0/4] drm: add raw monotonic timestamp support

[Imre Deak]

On Fri, 2012-10-05 at 16:07 -0700, Eric Anholt wrote:
> Imre Deak <imre.deak at intel.com> writes:
> 
> > This is needed to make applications depending on vblank/page flip
> > timestamps independent of time ajdustments.
> >
> > I've tested these with an updated intel-gpu-test/flip_test and will send
> > the update for that once there's no objection about this patchset.
> >
> > The patchset is based on danvet's dinq branch with the following
> > additional patches from the intel-gfx ML applied: 
> >     drm/i915: paper over a pipe-enable vs pageflip race
> >     drm/i915: don't frob the vblank ts in finish_page_flip
> >     drm/i915: call drm_handle_vblank before finish_page_flip
> 
> While people are in pageflip code:
> 
> It would be really, really cool for application tracing if we could get
> timestamps out of our swaps that used the TIMESTAMP register that is the
> timer used for event tracing on the GPU using GL_ARB_timer_query.  Then
> you could get decent visualizations of the latency of your rendering.

I assume this querying wouldn't be done through the wait_for_vblank or
page_flip ioctls, but rather a new ioctl or even through a new perf
event? We could add such a new interface later; this patchset is more
focused on the above two ioctls.

--Imre