linux-kernel - Re: [RFC v3 00/12] DRM scheduling cgroup controller

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Date:   Thu, 26 Jan 2023 18:14:46 +0000
From:   Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>
To:     Tejun Heo <tj@...nel.org>,
        Michal Koutný <mkoutny@...e.com>
Cc:     Intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johannes Weiner <hannes@...xchg.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Dave Airlie <airlied@...hat.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Rob Clark <robdclark@...omium.org>,
        Stéphane Marchesin <marcheu@...omium.org>,
        "T . J . Mercier" <tjmercier@...gle.com>, Kenny.Ho@....com,
        Christian König <christian.koenig@....com>,
        Brian Welty <brian.welty@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...el.com>
Subject: Re: [RFC v3 00/12] DRM scheduling cgroup controller

On 26/01/2023 17:57, Tvrtko Ursulin wrote:
> On 26/01/2023 17:04, Tejun Heo wrote:

>> driver folks think about the current RFC tho. Is at least AMD on board 
>> with
>> the approach?
> 
> Yes I am keenly awaiting comments from the DRM colleagues as well.

Forgot to mention one thing on this point which may interest AMD.

Some time ago I tested the super primitive "throttling via lowering the 
scheduling priority" on a GuC based i915 GPU, so only three supported 
priority levels, and FWIW it can be somewhat effective.

It certainly was effective for my main use case which is "run this GPU 
workload in the background while I use the GPU for something else".

The actual test was along the lines of running a GPU hog in parallel to 
an interactive client which can measure dropped frames.

With equal drm.weights the interactive client was seeing ~10 (i915 
pre-GuC) or ~27 (i915 GuC) dropped frames per second (60 fps target). 
With the GPU hog drm.weight lowered to 1:10 that dropped to ~3 dropped 
frames per second (all 3 before the over budget condition was noticed by 
the controller).

Main take here is that improved user experience is possible even with 
this primitive throttling method and even on GPUs which support only 
three scheduling priority levels.

Although main thing still is that individual drivers are completely free 
to improve their method of handling to the over budget signal. Nothing 
in the controller itself should be precluding that.

Regards,

Tvrtko