[PATCH 3/3] drm: do not sleep on vblank while holding a mutex

Daniel Vetter daniel at ffwll.ch
Fri Oct 28 02:20:32 PDT 2011

On Fri, Oct 28, 2011 at 08:59:04AM +0200, Michel Dänzer wrote:
> On Don, 2011-10-27 at 22:19 -0500, Ilija Hadzic wrote: 
> > On Thu, 27 Oct 2011, Daniel Vetter wrote:
> > 
> > > So I think the right thing to do is
> > > - Kill dev->last_vblank_wait (in a prep patch).
> > 
> > Agreed. Also drm_vblank_info function can go away
> Actually, I was rather going to submit a patch to hook it up again —
> AFAICT it was unhooked without any justification. It could be useful for
> debugging vblank related hangs. Any issues with it, such as
> last_vblank_wait not being guaranteed to really be the last one, can
> always be improved later on.

I've thought a bit about the usefulness of it for debugging before
proposing to kill it and I think it can die: It's only really useful for a
complete hangs, if we have an issue we just missing a wakeup somewhere,
that's not gonna catch things. Hence I think something that allows you to
watch things while it's running is much better, i.e. either a drm debug
prinkt or a tracecall.

But if you're firmly attached to that debug file it should be pretty easy
to shove that under the protection of one of the vblank spinlocks.
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48

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