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

[Peter Clifton]

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.

-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)
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