[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 #20 from Kai <kai at dev.carbon-project.org> ---
Created attachment 125820
  --> https://bugs.freedesktop.org/attachment.cgi?id=125820&action=edit
dmesg output with additional debug info from attachment 125808

(In reply to Alex Deucher from comment #16)
> Does just reverting this chunk fix the issue?
> 
> @@ -1630,6 +1631,9 @@ int radeon_modeset_init(struct radeon_device *rdev)
>  
>         rdev->ddev->mode_config.funcs = &radeon_mode_funcs;
>  
> +       if (radeon_use_pflipirq == 2 && rdev->family >= CHIP_R600)
> +               rdev->ddev->mode_config.async_page_flip = true;
> +
>         if (ASIC_IS_DCE5(rdev)) {
>                 rdev->ddev->mode_config.max_width = 16384;
>                 rdev->ddev->mode_config.max_height = 16384;

Yes, just removing the default enable here has the same effect as reverting the
entire patch.

(In reply to Michel Dänzer from comment #18)
> Created attachment 125808
> 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.

Here you go. That was generated by running XCOM 2.

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

Haven't tested that yet. Maybe somebody else can do that. ;-)

(In reply to Michel Dänzer from comment #19)
> BTW, there are some potential workarounds:
> 
> * Disable DRI3 for affected games with the environment variable
>   LIBGL_DRI3_DISABLE=1
> 
> * Enable sync-to-vblank in affected applications, or force it with
> vblank_mode=3

Well, this is going to be odd: I had VSync enabled in XCOM, since without that
option I got poorer performance in the past than with it. Now, after your note
here I actually *disabled* the VSync option in the game. 4.6.4 (or 4.7.0
without the offending commit/the enable removed) shows no longer a performance
difference and I'm getting ~30 FPS in XCOM 2. BUT with your ASYNC patch
(vanilla 4.7.0) and VSync turned of in the game gives me ALSO ~30 FPS! I'd
still say this is a regression as there is no difference without your patch,
but maybe this information can help you in narrowing down the cause?

I hope I haven't missed any open question. Let me know if you need anything
else.

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