[Bug 101769] 2X performance regression on Mesa 17.1 vs 17.0

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101769

--- Comment #1 from Matias N. Goldberg <dark_sylinc at yahoo.com.ar> ---
I was going to submit a new bug report, but I suspect this is the same issue.

I recently purchased an i7 7700 + Radeon RX 560 2GB to replace my older i5 4650
+ Radeon HD 7770.
But I noticed performance on Dolphin Emulator *went down*. Way down when using
OpenGL; whereas Vulkan has no performance issues and running on Windows gives
similar performance to Linux with Vulkan.

But what's more baffling is the performance with our Ogre 2.1 samples:
1. If I run our Postprocessing sample I can easily obtain 500 fps.
2. But if certain processes are running on the background, such as RenderDoc
with a capture (even if RenderDoc is minimized), the framerate will go down as
low as 55-69fps; with CPU usage around 3% and radeontop indicating a GPU usage
of 15%. This behavior is a little inconsistent, as closing RenderDoc will
increase performance back to 500 fps, but opening RenderDoc again will keep it
at 500 fps. RenderDoc is not the only process to induce this mysterious
behavior, but it is the one I've managed to identify correctly.

At first I suspected a clocking problem, but after setting CPU governor to
performance and echo high >
/sys/class/drm/card0/device/power_dpm_force_performance_level the problem
persisted.

The framerate drops aren't also consistent, another of our samples for example
reduces their performance from 200fps to 40fps.
Dolphin should be performing between 100-200 fps (by comparing with Vulkan and
Windows versions) but it manages between 21-49fps

I will try to see if older versions of Mesa as this ticket suggests will solve
the problem; although I'm not sure if Mesa 17.0.0 supports Polaris.

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