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

Christian König
2016-07-07T07:58:05Z

Am 07.07.2016 um 05:32 schrieb Michel Dänzer:
> On 06.07.2016 22:45, Tejun Heo wrote:
>> On Wed, Jul 06, 2016 at 12:12:52PM +0900, Michel Dänzer 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.