linux-kernel - Re: [PATCH 2/6] sched/fair: remove unused parameter of update_nohz

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Date:   Tue, 9 Feb 2021 14:45:15 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org,
        bsegall@...gle.com, mgorman@...e.de, fweisbec@...il.com,
        tglx@...utronix.de, bristot@...hat.com,
        linux-kernel@...r.kernel.org, joel@...lfernandes.org
Cc:     qais.yousef@....com
Subject: Re: [PATCH 2/6] sched/fair: remove unused parameter of
 update_nohz_stats

On 05/02/2021 12:48, Vincent Guittot wrote:
> idle load balance is the only user of update_nohz_stats and doesn't use
> force parameter. Remove it

Wasn't the 'force=true' from ilb eclipsing the jiffy resolution rate
limiting '!time_after(jiffies, rq->last_blocked_load_update_tick)' of
update_blocked_averages()?

So IMHO this has the (maybe intended) side effect that (formerly forced
updates) are now rate limited on one jiffy resolution too.

> 
> 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 bfe1e235fe01..60b8c1c68ab9 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);
> @@ -10404,7 +10404,7 @@ static bool _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);
>  
>  		/*
>  		 * If time for next balance is due,
>