[Bug 101182] Reading amdgpu_pm_info causes stutter with Linux 4.12-rc

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101182

            Bug ID: 101182
           Summary: Reading amdgpu_pm_info causes stutter with Linux
                    4.12-rc
           Product: DRI
           Version: DRI git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: haagch at frickel.club

A stutter once wouldn't be so bad, but apps like radeon-profile repeatedly read
this file, so rendering stutters constantly.

You will have a hard time spotting it in the average fps graph, but with my
(still very inaccurate) low-fps patch at
https://github.com/ChristophHaag/mesa-mesa/commit/e097b91a85c85718576589402e075e7f5668e68c
it's very visible that there is at least one frame that's delayed a lot each
time amdgpu_pm_info is read.
The GPU load does give an independent hint that something is wrong though.

To reproduce:
run  glxgears
run  sudo watch --interval=.3 cat /sys/kernel/debug/dri/0/amdgpu_pm_info
observe stuttering in glxgears.

RX 480, Linux 4.12-rc2.
I haven't tested 4.11 to confirm, but if I remember correctly, this happens in
mainline since 4.12.

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