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

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Message-ID: <20200611142806.GJ2531@hirez.programming.kicks-ass.net>
Date:   Thu, 11 Jun 2020 16:28:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>, 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
Subject: Re: [PATCH v2] sched/fair: fix nohz next idle balance

On Thu, Jun 11, 2020 at 03:12:11PM +0100, Valentin Schneider wrote:
> 
> On 09/06/20 13:37, 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>
> 
> FWIW:
> Reviewed-by: Valentin Schneider <valentin.schneider@....com>
> 
> Do we want a Fixes: tag for this? I'm thinking
> b7031a02ec75 ("sched/fair: Add NOHZ_STATS_KICK")

Done, thanks!