linux-kernel - Re: [PATCH 09/23] sched,ivtv: Convert to sched_set

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Message-ID: <20200422132604.GI20730@hirez.programming.kicks-ass.net>
Date:   Wed, 22 Apr 2020 15:26:04 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        qais.yousef@....com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, hverkuil@...all.nl,
        awalls@...metrocast.net
Subject: Re: [PATCH 09/23] sched,ivtv: Convert to sched_set_fifo*()

On Wed, Apr 22, 2020 at 08:53:45AM -0400, Steven Rostedt wrote:
> On Wed, 22 Apr 2020 13:27:28 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > Because SCHED_FIFO is a broken scheduler model (see previous patches)
> > take away the priority field, the kernel can't possibly make an
> > informed decision.
> > 
> > Effectively changes from 99 to 50.
> 
> I wonder for the 99 users, we should have a sched_set_high() that would set
> the task to something like 75.
> 
> That is, above default 50?

No. If userspace knows, userspace can fix it. We must not bother with
priority, simply because we cannot, possibly, say something useful.