[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 #13 from H Buus <ubuntu at hbuus.com> ---
(In reply to Chris Wilson from comment #12)
> (In reply to H Buus from comment #10)
> > I'm afraid https://patchwork.freedesktop.org/series/48379/ did not help.
> > 
> > I first tested without drm.debug set. FWIW, I noticed the cursor is briefly
> > displayed when playback starts and stops, but definitely not when I see the
> > stuttering.
> > 
> > I experimented with turning on mythtv's "hide cursor" option. Didn't help, I
> > still see stuttering. So I rebooted with debug enabled and log_buf_len=512K.
> > The output is in dmesg4.txt
> > 
> > I started playback after about 120 seconds from boot time, with "hide
> > cursor" disabled. Same stuttering. Stopped playback.
> > 
> > Some time after 190 seconds, I turned on the "hide cursor" option and even
> > unplugged the USB optical mouse I use when doing maintenance (never been
> > fond of touchpads). Then started playback. I still see stuttering.
> 
> Darn. How frequent is the stutter. The dmesg shows it is reprobing the
> displays (which will cause it to stutter) every 15s which is very odd, as
> that just happens to be the same as the ddx's cache. That suggests MythTV is
> constantly reprobing? Really, really odd.

It's definitely more often than 15 seconds, although it's possible there's a
greater stutter at 15 sec intervals. Like I said, it's slight, but noticeable
and distracting during panning. Also during zooms that are relatively slow &
smooth. There's also some variability in severity, from run to run. It might
not bother everyone, but it bothers me. I could try to record it using a 720p
camera mounted to a tripod. My phone would probably be better, but I don't have
a way to mount it to my tripod.

> One thing you can quickly try is to change the value reported for
> HAS_COHERENT_PHYS_GTT, say
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c
> b/drivers/gpu/drm/i915/i915_drv.c
> index 35a012ffc03b..175fdad11352 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -312,6 +312,7 @@ static int i915_getparam_ioctl(struct drm_device *dev,
> void *data,
>         case I915_PARAM_ALLOW_BATCHBUFFER:
>         case I915_PARAM_LAST_DISPATCH:
>         case I915_PARAM_HAS_EXEC_CONSTANTS:
> +       case I915_PARAM_HAS_COHERENT_PHYS_GTT:
>                 /* Reject all old ums/dri params. */
>                 return -ENODEV;
>         case I915_PARAM_CHIPSET_ID:
> @@ -411,7 +412,6 @@ static int i915_getparam_ioctl(struct drm_device *dev,
> void *data,
>         case I915_PARAM_HAS_PINNED_BATCHES:
>         case I915_PARAM_HAS_EXEC_NO_RELOC:
>         case I915_PARAM_HAS_EXEC_HANDLE_LUT:
> -       case I915_PARAM_HAS_COHERENT_PHYS_GTT:
>         case I915_PARAM_HAS_EXEC_SOFTPIN:
>         case I915_PARAM_HAS_EXEC_ASYNC:
>         case I915_PARAM_HAS_EXEC_FENCE:
> 
> and that will cause the ddx to use the same old pwrite interface it
> previously used. But I suspect the cursor is just my wild goose chase.

I'm compiling it now. Probably won't have results until late tonight or
tomorrow AM, EDT.

> > You mentioned looking at the ddx debug log. Is that the same as the "xorg
> > debug log (xf86-video-intel compiled with --enable-debug=full)" mentioned in
> > comment #5? If so, would it be sufficient to download and compile the
> > deb-src package that matches the binary version currently installed on the
> > laptop? It is called xserver-xorg-video-intel and is at version
> > 2:2.99.917+git20171229-1. That version contains the most recent tag albeit
> > from 4 years ago, and apparently has some patches from last December. Guess
> > I'm worried compiling from master could introduce ABI incompatibilities with
> > other xorg packages.
> 
> It's API compatible with Xorg-1.6 through 1.19 (there's one tiny change
> required for 1.20 and Prime offload :(, but not going to affect you.

So you'd prefer I compile from master, right? I'm experimenting with the source
package at the moment, but I can switch to a git repo. The deb source did help
installing required packages and giving me a starting point with configure.

> > Also, would I be correct in assuming the xorg/ddx debug log will go to
> > /var/log/Xorg.0.log?
> 
> Yes.

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