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

[Christian KÃnig]

Am 07.07.2016 um 05:32 schrieb Michel DÃnzer:
> On 06.07.2016 22:45, Tejun Heo wrote:
> > On Wed, Jul 06, 2016 at 12:12:52PM +0900, Michel DÃnzer wrote:
> >
> > > Not being very familiar with the workqueue APIs, I'll describe how it's
> > > supposed to work from a driver POV, which will hopefully help you guys
> > > decide on the most appropriate alloc_workqueue parameters.
> > >
> > > There is one flip work queue for each hardware CRTC. At most one
> > > radeon_flip_work_func item can be queued for any of them at any time.
> > > When a radeon_flip_work_func item is queued, it should be executed ASAP
> > > (so WQ_HIGHPRI might be appropriate?).
> > Hmmm... the only time WQ_HIGHPRI should be used is when it'd otherwise
> > require a kthread w/ nice value at -20.  Would that be the case here?
> > What are the consequences of the work item getting delayed?
> A page flip may be delayed to a later display refresh cycle.
>
>
> > 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.

Regards,
Christian.