[Bug 107600] Regression: stuttering H.264 video w/ mythtv on old laptop w/ 915GM igp

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=107600

--- Comment #9 from Chris Wilson <chris at chris-wilson.co.uk> ---
(In reply to H Buus from comment #8)
> (In reply to Chris Wilson from comment #7)
> > See https://patchwork.freedesktop.org/series/48379/
> 
> Many thanks for looking at this issue. I'm compiling with your patch now,
> but I'm unsure whether I'm supposed to do something about comment #5:
> 
> "Put a WARN in i915_gem_object_attach_phys() to see how frequently that code
> is being called. If it is being called, grab an xorg debug log
> (xf86-video-intel compiled with --enable-debug=full) for the next question
> is why. If not, the problem is nothing to do with the phys object."
> 
> My guess is comment #5 was your first thought to collect debugging info and
> then you had a better idea, namely this patch. So, I am assuming I should
> not put a WARN in i915_gem_object_attach_phys(). If you do want a WARN added
> to i915_gem_object_attach_phys(), I would appreciate a patch, because I am
> unfamiliar with kernel WARN macros and how to use them.

Stick with investigating the patch. I checked the ddx and afaict it should be
caching the cursor just fine, so the likely cause is aperture thrashing amongst
GTT mmaps rather than the cost of instantiating new physical cursors.

If the patch doesn't resolve it, then I think looking at the ddx debug log is
the next step. There we are just looking for how the cursor is being used.

> It wasn't clear to me, reading the commit msg for
> 6a2c4232ece145d8b5a8f95f767bd6d0d2d2f2bb, that it had anything to do with
> cursors (and I assume we're talking mouse cursors).

Physical objects are only used for 2 things, the register file for the overlay
plane (static, allocated on module load) and cursors which are dynamically
bound  objects.

> FWIW, the mythtv
> frontend/player normally doesn't display a cursor, unless the mouse is
> moved. The frontend does have an option to disable the mouse cursor
> entirely, which I have not enabled. It also has options to change the output
> mode, refresh rate, etc. based on the video being played, which I haven't
> enabled either. Those options are intended to take advantage of a display's
> deinterlacing capabilities (especially TVs), which I have never explored.

Yeah, which is why it was quite surprising. My guess is that even though you
don't see the cursor, it is redrawing an invisible cursor. That's all guess
work, but it's the only way I could connect the patch to MythTV. :|

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