On Thu, Oct 8, 2020 at 1:24 AM Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > On Wed, Oct 07, 2020 at 09:44:09AM -0700, Rob Clark wrote: > > On Mon, Oct 5, 2020 at 5:15 AM Ville Syrjälä > > <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > On Fri, Oct 02, 2020 at 10:55:52AM -0700, Rob Clark wrote: > > > > On Fri, Oct 2, 2020 at 4:05 AM Ville Syrjälä > > > > <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > On Fri, Oct 02, 2020 at 01:52:56PM +0300, Ville Syrjälä wrote: > > > > > > On Thu, Oct 01, 2020 at 05:25:55PM +0200, Daniel Vetter wrote: > > > > > > > On Thu, Oct 1, 2020 at 5:15 PM Rob Clark <robdclark@xxxxxxxxx> wrote: > > > > > > > > > > > > > > > > I'm leaning towards converting the other drivers over to use the > > > > > > > > per-crtc kwork, and then dropping the 'commit_work` from atomic state. > > > > > > > > I can add a patch to that, but figured I could postpone that churn > > > > > > > > until there is some by-in on this whole idea. > > > > > > > > > > > > > > i915 has its own commit code, it's not even using the current commit > > > > > > > helpers (nor the commit_work). Not sure how much other fun there is. > > > > > > > > > > > > I don't think we want per-crtc threads for this in i915. Seems > > > > > > to me easier to guarantee atomicity across multiple crtcs if > > > > > > we just commit them from the same thread. > > > > > > > > > > Oh, and we may have to commit things in a very specific order > > > > > to guarantee the hw doesn't fall over, so yeah definitely per-crtc > > > > > thread is a no go. > > > > > > > > If I'm understanding the i915 code, this is only the case for modeset > > > > commits? I suppose we could achieve the same result by just deciding > > > > to pick the kthread of the first CRTC for modeset commits. I'm not > > > > really so much concerned about parallelism for modeset. > > > > > > I'm not entirely happy about the random differences between modesets > > > and other commits. Ideally we wouldn't need any. > > > > > > Anyways, even if we ignore modesets we still have the issue with > > > atomicity guarantees across multiple crtcs. So I think we still > > > don't want per-crtc threads, rather it should be thread for each > > > commit. > > > > I don't really see any other way to solve the priority inversion other > > than per-CRTC kthreads. > > What's the problem with just something like a dedicated commit > thread pool? partly, I was trying to avoid re-implementing workqueue. And partly the thread-pool approach seems like it would be harder for userspace to find the tasks which need priority adjustment. But each CRTC is essentially a FIFO, pageflip N+1 on a given CRTC will happen after pageflip N. BR, -R > > I've been thinking about it a bit more, and > > my conclusion is: > > > > (1) There isn't really any use for the N+1'th commit to start running > > before the kthread_work for the N'th commit completes, so I don't mind > > losing the unbound aspect of the workqueue approach > > (2) For cases where there does need to be serialization between > > commits on different CRTCs, since there is a per-CRTC kthread, you > > could achieve this with locking > > > > Since i915 isn't using the atomic helpers here, I suppose it is an > > option for i915 to just continue doing what it is doing. > > > > And I could ofc just stop using the atomic commit helper and do the > > kthreads thing in msm. But my first preference would be that the > > commit helper does generally the right thing. > > > > BR, > > -R > > -- > Ville Syrjälä > Intel
