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Date:   Mon, 21 Sep 2020 12:49:47 +0200
From:   peterz@infradead.org
To:     Rob Clark <robdclark@gmail.com>, dri-devel@lists.freedesktop.org,
        Rob Clark <robdclark@chromium.org>,
        linux-arm-msm@vger.kernel.org,
        open list <linux-kernel@vger.kernel.org>, timmurray@google.com,
        Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 0/3] drm: commit_work scheduling
Message-ID: <20200921104947.GQ1362448@hirez.programming.kicks-ass.net>
References: <20200919193727.2093945-1-robdclark@gmail.com>
 <20200921092154.GJ438822@phenom.ffwll.local>
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On Mon, Sep 21, 2020 at 11:21:54AM +0200, Daniel Vetter wrote:

> So question to rt/worker folks: What's the best way to let userspace set
> the scheduling mode and priorities of things the kernel does on its
> behalf? Surely we're not the first ones where if userspace runs with some
> rt priority it'll starve out the kernel workers that it needs. Hardcoding
> something behind a subsystem ioctl (which just means every time userspace
> changes what it does, we need a new such flag or mode) can't be the right
> thing.
> 
> Peter, Tejun?

So regular workqueues do not support RT priorities, but you can set
their nice value somewhere in /sys.

The kthread_work stuff used in these patches result in a regular kthread
and as such the user interface for changing its scheduling class or
priority is that of any other 'random' task.