[Bug 81682] [snb] Frequent framerate drops

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=81682

--- Comment #2 from Greg Sutcliffe <bugsfreedesktop at emeraldreverie.org> ---
Thanks Chris, with your help on IRC I got a custom kernel and the overlay
working.
In case it matters, I'm using 3.16.0-rc6-290399-gd4990be with i915 builtin.

Running Space Hulk, typically the GPU seems to sit at 1000-1100MHz and consumes
~1100mW power. When the issue strikes, all the graphs show a substantial drop -
power drops to 600mW, freq to 650MHz and frame rate goes through the floor.
Interestingly the purple CPU graph in the top right shows an uptick in usage at
the same time (typically jumping from 100-120% busy to 200-240% busy, but has
been as high as 500% busy), but I can't find a separate process that might be
responsible for that. Top reports the game, firefox, and intel-gpu-overlay as
the top three process during such a slowdown.

I've taken a few screenshots using my mobile phone - terrible, I know, but
since the overlay is outside the normal display system, my usual screenshot
tools can't capture it. Happy to re-do them if there's a better way to capture
the images. I've also attached my xorg config and kernel module config for
i915, in case it's useful.

What's next to investigate?

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