[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 #12 from Chris Wilson <chris at chris-wilson.co.uk> ---
(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.

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.

> 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.

> 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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