[Intel-gfx] Modesetting bug on 945GSE (Atom N270) with Chris Wilson drm-intel-next kernel

[Simon Farnsworth]

On Tuesday 23 November 2010, Simon Farnsworth <simon.farnsworth at onelan.co.uk> 
wrote:
> So, I looked at this a bit; started by using:
> ./perf record -e sched:sched_wakeup -e sched:sched_switch -e
> i915:i915_flip_request -e i915:i915_flip_complete -e
> i915:i915_gem_request_wait_begin -a
> 
> to record traces, and viewed them with perf trace, to check that I was on
> the right sort of track. I then tried perf timechart, just to see what the
> output looks like, but found that 8GB RAM and 10GB swap isn't enough space
> for Inkspace, Google Chrome or Firefox to examine the resulting SVG.
> 
> I'm therefore just using perf trace to look at deadline misses; the record
> command above gives you enough data to see who's pushed you off the CPU and
> thus determine why you couldn't make your deadline, albeit not nicely
> presented.
> 
And I've just found the perf trace hooks to let a python script help print 
traces - I knew the kernel guys were normally a few steps ahead of me. Run the 
attached script via:
perf trace -s /path/to/i915-crisis.py

It changes the printed timings to be relative to the most recent flip_complete; 
you can thus see what's running when within your crisis period, and how close 
you get to running out of time. Using it, I've seen that I'm taking 10-12 
milliseconds to draw after a flip, and thus usually only seeing 30 frames a  
second on a 60Hz refresh display.
-- 
Simon Farnsworth
Software Engineer
ONELAN Limited
http://www.onelan.com/
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