linux-kernel - Re: [PATCH 3/7 v4] sched/fair: remove unused parameter of update_nohz

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Date:   Fri, 5 Mar 2021 13:55:58 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org,
        joel@...lfernandes.org, valentin.schneider@....com,
        fweisbec@...il.com, tglx@...utronix.de
Subject: Re: [PATCH 3/7 v4] sched/fair: remove unused parameter of
 update_nohz_stats

On 02/24/21 14:30, Vincent Guittot wrote:
> idle load balance is the only user of update_nohz_stats and doesn't use
> force parameter. Remove it
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  kernel/sched/fair.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e23709f6854b..f52f4dd3fb9e 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8352,7 +8352,7 @@ group_type group_classify(unsigned int imbalance_pct,
>  	return group_has_spare;
>  }
>  
> -static bool update_nohz_stats(struct rq *rq, bool force)
> +static bool update_nohz_stats(struct rq *rq)
>  {
>  #ifdef CONFIG_NO_HZ_COMMON
>  	unsigned int cpu = rq->cpu;
> @@ -8363,7 +8363,7 @@ static bool update_nohz_stats(struct rq *rq, bool force)
>  	if (!cpumask_test_cpu(cpu, nohz.idle_cpus_mask))
>  		return false;
>  
> -	if (!force && !time_after(jiffies, rq->last_blocked_load_update_tick))
> +	if (!time_after(jiffies, rq->last_blocked_load_update_tick))
>  		return true;
>  
>  	update_blocked_averages(cpu);
> @@ -10401,7 +10401,7 @@ static void _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
>  
>  		rq = cpu_rq(balance_cpu);
>  
> -		has_blocked_load |= update_nohz_stats(rq, true);
> +		has_blocked_load |= update_nohz_stats(rq);

I think Dietmar commented on this on v1. There's a change in behavior here
AFAICT. Worth expanding the changelog to explain that this will be rate limited
and why it's okay? It'll help a lost soul like me who doesn't have the ins and
outs of this code carved in their head :-)

Thanks

--
Qais Yousef


>  
>  		/*
>  		 * If time for next balance is due,
> -- 
> 2.17.1
>