linux-kernel - Re: [PATCH] drm/radeon: Remove deprecated create_singlethread

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Date:	Thu, 7 Jul 2016 09:43:26 +0200
From:	Christian König <christian.koenig@....com>
To:	Michel Dänzer <michel@...nzer.net>,
	Tejun Heo <tj@...nel.org>
CC:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>,
	Alex Deucher <alexander.deucher@....com>,
	<dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/radeon: Remove deprecated
 create_singlethread_workqueue

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.