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From:   Valentin Schneider <valentin.schneider@arm.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de,
        rostedt@goodmis.org, qais.yousef@arm.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        bsegall@google.com, mgorman@suse.de, daniel.lezcano@linaro.org,
        sudeep.holla@arm.com
Subject: Re: [PATCH 06/23] sched,psci: Convert to sched_set_fifo*()
In-reply-to: <20200422112831.574539982@infradead.org>
Date:   Wed, 22 Apr 2020 12:55:53 +0100
Message-ID: <jhjtv1bloom.mognet@arm.com>
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On 22/04/20 12:27, Peter Zijlstra 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 prio from 99 to 50.
>
> XXX this thing is horrific, it basically open-codes a stop-machine and
> idle.
>

I went and tried to clean up the thing. I didn't find a clean way to use
stop_machine() + play_idle() (stoppers can't sleep), but I did manage to
get something usable with the existing FIFO threads, play_idle_precise()
and the cpuidle state usage stats, so the whole homebrewed idle thing can
go.

I also just tested it with 50 prio and big surprise it didn't change
anything (it ends up being sibling of idle injection). So FWIW:

Acked-by: Valentin Schneider <valentin.schneider@arm.com>

> Cc: daniel.lezcano@linaro.org
> Cc: sudeep.holla@arm.com
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Ingo Molnar <mingo@kernel.org>