linux-kernel - Re: [PATCH] sched/rt: Do not do push/pull when there is only one CPU

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Message-ID: <20171202121252.0bada310@vmware.local.home>
Date:   Sat, 2 Dec 2017 12:12:52 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Daniel Wagner <wagi@...om.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] sched/rt: Do not do push/pull when there is only one
 CPU

On Sat, 2 Dec 2017 13:53:31 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> what about a check next to sched_feat(RT_PUSH_IPI)? I don't know if this
> is a hot path or not (due to bitmap_weight). If it is, then I would
> suggest something like a jump-label which is enabled if more than one
> CPU has been enabled on boot.

Yeah I didn't like that because of the overhead. But I was being
optimistic that the cpu weight function would be a nit to the actual
pull logic. But I have a better plan.

I would like to disable RT_PUSH_IPI, but that's a sched feature and
that is a constant if we build without sched debugging.

v2 coming up.

-- Steve