[Bug 100742] dpm auto doesn't clock the GPU high enough for SteamVR apps

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=100742

            Bug ID: 100742
           Summary: dpm auto doesn't clock the GPU high enough for SteamVR
                    apps
           Product: DRI
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: haagch@frickel.club

RX 480, Ryzen 1600X, tested on linux 4.10 and linux drm-next-4.12-wip, latest
upstream linux-firmware git. Same behavior on both kernels.

I recorded this video, showing umr top, sclk and mclk, while running the simple
"Atlas Demo Scene" in the Destinations SteamVR app:

https://www.youtube.com/watch?v=U_mceDSBF7o

With the "auto" setting the GPU power level is not set high enough for SteamVR
to render at the Vive's native 90 fps, so reprojection (interpolation to 90
fps) needs to kick in constantly.

Speculation time:
The SteamVR frametime graph shows the purple GPU load from the application
("Destinations") completely below the 11 ms which the application is probably
is probably targeting, so dpm has clocked the GPU fast enough for the
application to run at 90 fps. But then the application submits frames to the
SteamVR compositor which also takes some GPU time and pushes the "total" GPU
time taken to render one frame in the app and then display it in the compositor
over the target 11 ms time.

Is this correct? Does dpm somehow analyze a per process GPU load? At least in
this case the GPU needs to clock fast enough to allow the application + the
SteamVR compositor to both render in under 11 ms per frame.

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