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From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Wed, 4 Mar 2020 12:55:21 +0100
Message-ID: <CAKfTPtDrSzET+=G7rHvhDY3491CzGvp3ZqW0cqR8jhC1EvC2mQ@mail.gmail.com>
Subject: Re: [RFC PATCH] sched: fix the nonsense shares when load of cfs_rq is
 too, small
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     =?UTF-8?B?546L6LSH?= <yun.wang@linux.alibaba.com>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        "open list:SCHEDULER" <linux-kernel@vger.kernel.org>
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On Wed, 4 Mar 2020 at 10:52, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Wed, Mar 04, 2020 at 09:47:34AM +0100, Vincent Guittot wrote:
> > you will add +1 of nice prio for each device
> >
> > should we use instead
> > # define scale_load_down(w) ((w >> SCHED_FIXEDPOINT_SHIFT) ? (w >>
> > SCHED_FIXEDPOINT_SHIFT) : MIN_SHARES)
>
> That's '((w >> SHIFT) ?: MIN_SHARES)', but even that is not quite right.
>
> I think we want something like:
>
> #define scale_load_down(w) \
> ({ unsigned long ___w = (w); \
>    if (___w) \
>      ____w = max(MIN_SHARES, ___w >> SHIFT); \
>    ___w; })
>
> That is, we very much want to retain 0 I'm thinking.

yes, you're right