Hello,
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?
Thanks.