linux-kernel - Re: [PATCH v2] sched/fair: fix nohz next idle balance

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Message-ID: <20200610124921.GD2497@hirez.programming.kicks-ass.net>
Date:   Wed, 10 Jun 2020 14:49:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        linux-kernel@...r.kernel.org, iwtbavbm@...il.com,
        valentin.schneider@....com
Subject: Re: [PATCH v2] sched/fair: fix nohz next idle balance

On Tue, Jun 09, 2020 at 02:37:48PM +0200, Vincent Guittot wrote:
> With commit:
>   'b7031a02ec75 ("sched/fair: Add NOHZ_STATS_KICK")'
> rebalance_domains of the local cfs_rq happens before others idle cpus have
> updated nohz.next_balance and its value is overwritten.
> 
> Move the update of nohz.next_balance for other idles cpus before balancing
> and updating the next_balance of local cfs_rq.
> 
> Also, the nohz.next_balance is now updated only if all idle cpus got a
> chance to rebalance their domains and the idle balance has not been aborted
> because of new activities on the CPU. In case of need_resched, the idle
> load balance will be kick the next jiffie in order to address remaining
> ilb.
> 
> Reported-by: Peng Liu <iwtbavbm@...il.com>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>

Thanks