[Intel-gfx] Increased latency from removal of GEM_THROTTLE in 2D driver

[Eric Anholt]

On Sat, 06 Nov 2010 01:44:59 +0000, Peter Clifton <pcjc2 at cam.ac.uk> wrote:
> I've been playing with my app again, and whilst it seems a tiny bit
> faster in benchmarks, since the 2D driver change:
> 
> commit 8ff37667bf864b771d16a58fc5041cb48408b6a8
> Author: Eric Anholt <eric at anholt.net>
> Date:   Tue Nov 2 10:36:03 2010 -0700
> 
>     Remove the intermittent GEM_THROTTLE call.
> 
> 
> I've noticed the latency / interactivity is WAY down, and I've also had
> intermittent GPU hangs whilst benchmarking which I'd never seen before. 
> 
> It might be unrelated (as I'm running a back-ported drm-intel-next, and
> just pulled it up to date), but for a quick check, I just reverted to a
> previous 2D driver just prior to the above commit, and interactivity has
> improved a lot (I don't have a number for it, just from testing).
> 
> Presumably this says something bad about my app, or its benchmarking
> code. Any clues as to what that is?
> 
> Without the commit, I can use other X11 apps whilst my PCB program is
> benchmarking. With it, the X11 server graphics almost completely freeze
> up.

I'm seeing this too, with vblank_mode=0 and various apps.  Something
appears to be broken with the swapbuffers waits in the GL driver,
perhaps.
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