[Bug 97260] [bisected] R9 290 low performance in Linux 4.7

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97260

--- Comment #18 from Michel Dänzer <michel at daenzer.net> ---
Created attachment 125808
  --> https://bugs.freedesktop.org/attachment.cgi?id=125808&action=edit
radeon: Add some page flip debugging output

Well, that's a surprising result of the bisection.

I can imagine two possible causes, or possibly some combination thereof:

* The processing of asynchronous flips or the corresponding completion
interrupts
  is delayed for some reason
* Using flips instead of blits for buffer swaps lowers the load on the GPU 3D
  engine, so the SMU doesn't switch to higher clocks

The attached debugging patch should give us more information about the former.
With it applied, run the following while an affected application is running in
fullscreen:

sudo sh -c 'echo 2 >/sys/module/drm/parameters/debug'; sleep 1; sudo sh -c
'echo 0 >/sys/module/drm/parameters/debug'

Then attach the resulting dmesg output.

BTW, does the problem still happen with Alex's current drm-next-4.9-wip branch?

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