Re: [PATCH] drm/radeon: Remove deprecated create_singlethread_workqueue

From: Tejun Heo
Date: Tue Jul 12 2016 - 13:53:02 EST


On Fri, Jul 08, 2016 at 02:52:30PM +0900, Michel Dänzer wrote:
> On 07.07.2016 16:43, Christian König wrote:
> >>> Also, what kind of delays matter here? Is it millisec range or micro?
> >> It can be the latter in theory, but normally rather the former.
> >
> > Well to be precise with a typical 1920x1080@60 resolution you have about
> > 2.16ms time under ideal conditions for the flip.
> >
> > So using the high priority queue still sounds like a good idea to me.
> How did you arrive at 2.16ms?
> Userspace can call the ioctl up to one full refresh cycle ahead of time,
> which is ~16ms at 60 Hz. On the other hand userspace can also call the
> ioctl arbitrarily close to the vertical blank period, in which case even
> a delay of just 1ms (or even significantly less) may cause the flip to
> be delayed by one refresh cycle.

If there's too long a delay, the outcome is missing the refresh cycle,
right? Hmmm... yeah, WQ_HIGHPRI probably is the right answer here.
Bhaktipriya, can you please update the patch to use a dedicated
workqueue with WQ_HIGHPRI?