[Intel-gfx] output stutters

[Chris Wilson]

On Wed, Jun 10, 2015 at 06:33:49AM -0400, Brian J. Murrell wrote:
> On Sun, 2015-06-07 at 13:11 -0400, Brian J. Murrell wrote:
> > I have an:
> > 
> > 00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller (rev 06)
> > 
> > in a Fedora 21 machine running Linux 4.0.4.
> > 
> > While this is all generally working, the display has pauses where there
> > should be fluid motion.  Watching a video with mplayer for example,
> > plays about a second or so, then pauses for .25 to .5 (just a guess) of
> > a second and then continues playing.  glxgears does the same thing.
> > While it's reporting ~60fps the gears turn then stop then turn then
> > stop.
> > 
> > I see the same thing dragging windows across the screen or even just
> > scrolling (GTK3) application windows.
> > 
> > I'm using both the DVI and the VGA output of this card, FWIW.
> > 
> > What additional information can I provide to help diagnose this problem?
> 
> Is there anything I can do to help debug what this issue is?
> 
> The pauses translate into sponginess and latencies that make using this
> display very unpleasant.  :-(

sudo perf record -g -a -c 1 -e i915:i915_gem_request_wait_begin is
likely to capture the culprit. Though to be precise you need to look at
wait_begin + wait_end to measure the stall (some waits are more harmless
than others). As a first approximation just using perf will be good
enough to get a few leads.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre