[PATCH 4/5] drm/amdgpu: MCBP based on DRM scheduler (v8)

[Michel Dänzer]

On 2022-11-03 03:58, Zhu, Jiadong wrote:
> [AMD Official Use Only - General]
> 
>> The bad news is that this series still makes some things very slow. The most extreme examples so far are glxgears (runs at ~400 fps now, ~7000 fps before, i.e. almost 20x slowdown) and hexchat (scrolling one page now takes ~1 second, I can see it drawing line by line; before it was almost instantaneous). I suspect this series makes the overhead of running a single GPU job much bigger. On the bright side, I'm not noticing any significant intermittent freezes anymore.
> 
> Hi Michel,
> 
> Thanks for the trying.
> Is there high priority jobs running while executing glxgears?

Yes, mutter is submitting high priority jobs. However, I don't think that can explain the problem by itself:

mutter only draws once per display refresh cycle. Let's assume mutter's GPU work takes ~6-7ms (conservative example, should be less than that usually). That leaves ~10ms per display refresh cycle (at 60 Hz refresh rate) where GPU work from glxgears & Xwayland can run without getting preempted. Since glxgears runs at ~7000 fps without this series, it should be able to draw at least ~70 frames in 10ms[0], which corresponds to over 4000 fps. Yet it manages only 1/10 of that.

[0] Worst case consideration, ignoring the fact that without this series, glxgears runs at ~7000 fps while mutter sustains 60 fps.


> I am running glxgears while submitting high priority ibs using amdgpu_test, the fps ranges from 6000~8000.

It's getting clear that artificial tests such as amdgpu_test don't suffice for evaluating the real-world impact of this kind of change.


> Continuous preemption and resubmission may cause the slow fps. Could you have a check about how fast the trailing fence seqNo expands. On my side, the increment of Last signaled trailing fence is < 10 in a second.

I had to go back to a kernel without this series, as it was just unusable. As this is my main machine, I don't know when I'll get a chance to check this.


-- 
Earthling Michel Dänzer            |                  https://redhat.com
Libre software enthusiast          |         Mesa and Xwayland developer