[Bug 111987] Unstable performance (periodic and repeating patterns of fps change) and changing VDDGFX

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111987

            Bug ID: 111987
           Summary: Unstable performance (periodic and repeating patterns
                    of fps change) and changing VDDGFX
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: not set
          Priority: not set
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: witold.baryluk+freedesktop at gmail.com

AMD Radeon Fury X.

Linux debian 5.2.0-3-amd64 #1 SMP Debian 5.2.17-1 (2019-09-26) x86_64 GNU/Linux

ii  xserver-xorg-video-radeon                                   1:19.0.1-1     
                      amd64        X.Org X server -- AMD/ATI Radeon display
driver
ii  xserver-xorg-video-amdgpu                                   19.0.1-1       
                      amd64        X.Org X server -- AMDGPU display driver
ii  xserver-xorg-video-radeon                                   1:19.0.1-1     
                      amd64        X.Org X server -- AMD/ATI Radeon display
driver
ii  libdrm-radeon1:amd64                                        2.4.99-1        
amd64        Userspace interface to radeon-specific kernel DRM services --
runtime
ii  libdrm-amdgpu1:amd64                                        2.4.99-1       
                      amd64        Userspace interface to amdgpu-specific
kernel DRM services -- runtime


I was able to reproduce the issue in few titles:

Overwatch (64-bit Windows game) with various Wine and DXVK versions, as well
when using Wine OpenGL renderer.
Talos (native 64 bit Linux game) with Vulkan renderer.

Tested with both Mesa 19.2.1-1 with LLVM 9 from Debian, and custom compiled
Mesa 19.3.0-devel with LLVM 10 and ACO backend compilers.

If I setup the game to render constantly same things on screen (I do that by
simply going to a corner of the map, and looking at the ground or a corner,
where there is minimal amount of geometry and variability), I initially get
very high and stable frame rate, of lets say 105 FPS (plus minus 1 FPS).
However, if I wait long enough there are periodic (not sporadic, but actually
periodic, and exactly repeatable) situations where FPS drops. During that
period the GPU load increases from 30% to 100%, sometimes with one or two
intermediate steps (depends on the game and setup).

I also notice that the GPU VDD is changing during these period.

I eliminated all other sources of variability. Nothing running in background.

Reported GPU temperature is stable at <32 deg C, and during testing is stable
and flat.

Sometimes, if I keep the game running long enough, it will stabilize and stop
doing that. But sometimes if I wait long enough it will reenter this behaviour
back. Most of the time the behaviour is extremaly repetitive and predictable.
Not random.

Please see attached frametime graph (captured with modified Mesa vulkan
overlay) for Talos and Overatch.

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