linux-kernel - Re: [PATCH 6/7 v4] sched/fair: trigger the update of blocked load on newly idle cpu

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Date:   Fri, 5 Mar 2021 13:52:41 +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 6/7 v4] sched/fair: trigger the update of blocked load on
 newly idle cpu

On 02/24/21 14:30, Vincent Guittot wrote:
> +/*
> + * Check if we need to run the ILB for updating blocked load before entering
> + * idle state.
> + */
> +void nohz_run_idle_balance(int cpu)
> +{
> +	unsigned int flags;
> +
> +	flags = atomic_fetch_andnot(NOHZ_NEWILB_KICK, nohz_flags(cpu));
> +
> +	/*
> +	 * Update the blocked load only if no SCHED_SOFTIRQ is about to happen
> +	 * (ie NOHZ_STATS_KICK set) and will do the same.
> +	 */
> +	if ((flags == NOHZ_NEWILB_KICK) && !need_resched())
> +		_nohz_idle_balance(cpu_rq(cpu), NOHZ_STATS_KICK, CPU_IDLE);
> +}

nit: need_resched() implies this_cpu, but the function signature implies you
could operate on any CPU. Do need_resched() outside this function or make
the function read smp_processor_id() itself without taking an arg?

Thanks

--
Qais Yousef