On 2020-03-12 7:25 a.m., Simon Ser wrote: > On Thursday, March 12, 2020 11:45 AM, Michel Dänzer <michel@xxxxxxxxxxx> wrote: > >> On 2020-03-11 9:09 p.m., Simon Ser wrote: >> >>> Hi all, >>> I've been working on adding VRR support to Sway [1] (a Wayland >>> compositor). The compositor just sets the VRR_ENABLED property. >>> This works fine for some screens, but causes flcikering for other >>> screens as expected [2]. Fixing the flickering is something we've >>> talked about last XDC [3]. The flickering is caused by physical >>> limitations of the screen: changing the refresh rate too quickly >>> results in brightness issues. >>> The approach taken by xf86-video-amdgpu is to only enable VRR if an app >>> is fullscreen and not present in a special Mesa blacklist (e.g. Firefox >>> is in the blacklist because it doesn't render at a fixed interval). >>> For Wayland, I'd prefer to avoid having a blacklist. I'd like to be >>> able to use VRR in the general case (not just for fullscreen apps). >>> A way to fix the flickering would be to implement a slew rate and make >>> it so refresh rate variations are capped by the slew rate. >> >> One potential issue I see with this is the cursor, which can feel >> awkward if it only moves at 30 Hz. I wonder if a slew rate which can >> reliably prevent flickering allows the framerate to ramp up quickly >> enough for this not to be annoying. > > Thanks for pointing this out, that's a valid concern. > > My VRR monitor has a 40-60Hz VRR range. With the current Sway > implementation and drm_monitor [1], I can check that moving my mouse on > the monitor makes the refresh interval go from ~25ms to ~16.6ms (ie. > 40Hz to 60Hz). Right now there's no slew rate, so it goes from min to > max instantly. I don't notice any flickering and there's no lag. > > Looking at the list of monitors [2] on Wikipedia, it doesn't seem like > there's any monitor supporting less than 35Hz. > > We'd need to perform experiments on more hardware, but flickering has > been noticed by our users on higher-end monitors which support 144Hz. > I think the slew rate would prevent going from 35Hz to 144Hz directly, > but probably not from 40Hz to 60Hz. I think that would be acceptable. > > If it's not, we can always tweak the minimum refresh rate. > > tl;dr need to test on more hardware, but should probably be fine. Not the main VRR expert and we're still discussing this internally but I think it'll very much depend on the display whether you'll see flicker in this case. The other complication is that for gaming we don't want to use the cursor as a VRR trigger and only look at page flips in order to allow for smooth gameplay. For a desktop use-case that's probably not the right policy. Harry > > [1]: https://github.com/emersion/drm_monitor > [2]: https://en.wikipedia.org/wiki/FreeSync#List_of_supported_monitors > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
