linux-kernel - Re: [PATCH 3/9] sched/hotplug: Ensure only per-cpu kthreads run during hotplug

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Message-ID: <20201002142028.GY2628@hirez.programming.kicks-ass.net>
Date:   Fri, 2 Oct 2020 16:20:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     tglx@...utronix.de, mingo@...nel.org, linux-kernel@...r.kernel.org,
        bigeasy@...utronix.de, qais.yousef@....com, swood@...hat.com,
        valentin.schneider@....com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vincent.donnefort@....com
Subject: Re: [PATCH 3/9] sched/hotplug: Ensure only per-cpu kthreads run
 during hotplug

On Fri, Sep 25, 2020 at 06:38:50PM +0200, Dietmar Eggemann wrote:
> On 21/09/2020 18:36, Peter Zijlstra wrote:
> 
> [...]
> 
> > This replaces the unlikely(rq->balance_callbacks) test at the tail of
> > context_switch with an unlikely(rq->balance_work), the fast path is
> 
> While looking for why BALANCE_WORK is needed:
> 
> Shouldn't this be unlikely(rq->balance_callback) and
> unlikely(rq->balance_flags)?

But then we have two loads in the fastpath..