[Bug 74195] New: Responsivity to input with vsync on is slower after update

[Bug 74195] New: Responsivity to input with vsync on is slower after update

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https://bugs.freedesktop.org/show_bug.cgi?id=74195

          Priority: medium
            Bug ID: 74195
          Assignee: nouveau-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
           Summary: Responsivity to input with vsync on is slower after
                    update
        QA Contact: xorg-team-go0+a7rfsptAfugRpC6u6w@public.gmane.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: janjanjanx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: git
         Component: Driver/nouveau
           Product: xorg

I use compton compositing manager wich uses DRM_IOCTL_WAIT_VBLANK for vsync.
Recently I updated from kernel 3.9 to 3.13 and responsivness (or "input lag" or
however it's called) got much worse, mostly noticable when moving windows or
scrolling. With kernel 3.13 the windows are 3-5 frames behind mouse when
moving, on 3.9 kernel they were only 0-1 frames behind. I also tried kwin, wich
had less noticable slowdown (from 1-2 frames behind to 3-5 frames behind).

I tried different kernel versions from nouveau git and found out, that the
slowdown was caused by this commit:
http://cgit.freedesktop.org/nouveau/linux-2.6/commit/?id=0fa9061ae8c10a9178d696cf48d94c3bf2848f9f

I guess the commit is important and can't be undone, but the bad responsiveness
really annoys me, so I would be glad if there is a solution.

GPU is GTX 560 Ti
xserver 1.14.5
xorg-video-nouveau 1.0.10
libdrm 2.4.52
(Debian sid)

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[Bug 74195] [NVCE] Responsivity to input with vsync on is slower after update

[bugzilla-daemon-CC+yJ3UmIYqDUpFQwHEjaQ]

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https://bugs.freedesktop.org/show_bug.cgi?id=74195

Ilia Mirkin <imirkin-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Responsivity to input with  |[NVCE] Responsivity to
                   |vsync on is slower after    |input with vsync on is
                   |update                      |slower after update

--- Comment #1 from Ilia Mirkin <imirkin-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org> ---
On the surface, this should have been a no-op change. You say you tried
different kernel versions... is that to say you did a git bisect? e.g. can you
confirm that 0fa9061ae8c10a9178d696cf48d94c3bf2848f9f has the issue but
0fa9061ae8c10a9178d696cf48d94c3bf2848f9f^ doesn't?

One small difference that I noticed is that if stat == ~0 in the old code it'll
return IRQ_NONE, whereas it will try to handle it in after the patch. I can't
imagine that matters here though.

Something to look at is what it is that the drm framework provided with the
irq's that's not done by nouveau now.

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[Bug 74195] [NVCE] Responsivity to input with vsync on is slower after update

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https://bugs.freedesktop.org/show_bug.cgi?id=74195

--- Comment #2 from Jan Janecek <janjanjanx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
I can confirm that 0fa9061ae8c10a9178d696cf48d94c3bf2848f9f has the problem and
b9a3140ce8fcd616b02533fbdef375a87a910daf (previous commit) does'nt.

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[Bug 74195] [NVCE] Responsivity to input with vsync on is slower after update

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https://bugs.freedesktop.org/show_bug.cgi?id=74195

--- Comment #3 from Ilia Mirkin <imirkin-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org> ---
Actually the current code handles the intr == ~0 bit. The only other thing of
mild consequence is that drm_device->irq_enabled is no longer set.

Can you try adding

dev->irq_enabled = true;

to nouveau_drm.c:nouveau_drm_load somewhere after things look like they
succeed? Or perhaps right before the nouveau_display_create, where it was
before the patch. [And in an ideal world, one would also set it to false at
some point, e.g. nouveau_drm_unload, but I doubt that's important for this
experiment.]

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[Bug 74195] [NVCE] Responsivity to input with vsync on is slower after update

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https://bugs.freedesktop.org/show_bug.cgi?id=74195

--- Comment #4 from Jan Janecek <janjanjanx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
(In reply to comment #3)
> Actually the current code handles the intr == ~0 bit. The only other thing
> of mild consequence is that drm_device->irq_enabled is no longer set.
> 
> Can you try adding
> 
> dev->irq_enabled = true;
> 
> to nouveau_drm.c:nouveau_drm_load somewhere after things look like they
> succeed? Or perhaps right before the nouveau_display_create, where it was
> before the patch. [And in an ideal world, one would also set it to false at
> some point, e.g. nouveau_drm_unload, but I doubt that's important for this
> experiment.]

This fix solved the problem for 0fa9061ae8c10a9178d696cf48d94c3bf2848f9f!
That's great!

I will try if it works for 3.13 too.

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[Bug 74195] [NVCE] Responsivity to input with vsync on is slower after update

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https://bugs.freedesktop.org/show_bug.cgi?id=74195

--- Comment #5 from Jan Janecek <janjanjanx-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
Yes, the fix works for 3.13 too. Thank you so much!

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[Bug 74195] [NVCE] Responsivity to input with vsync on is slower after update

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https://bugs.freedesktop.org/show_bug.cgi?id=74195

--- Comment #6 from Emil Velikov <emil.l.velikov-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
Great catch Ilia,

from the DocBook [1]

Manual IRQ Registration
  ... They must set the
  <structname>drm_device</structname> <structfield>irq_enabled</structfield>
  field to 1 upon registration of the IRQs, and clear it to 0 after
  unregistering the IRQs.


[1]
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/DocBook/drm.tmpl#n374

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[Bug 74195] [NVCE] Responsivity to input with vsync on is slower after update

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https://bugs.freedesktop.org/show_bug.cgi?id=74195

Ilia Mirkin <imirkin-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #7 from Ilia Mirkin <imirkin-FrUbXkNCsVf2fBVCVOL8/A@public.gmane.org> ---
The fix is now upstream and will be included in the next 3.14-rc as well as be
backported to the affected stable kernels.

https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7d3428cd4b2ad51af86fdbdf8284ca38fa95e601

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