linux-kernel - Re: [PATCH 2/2] sched/fair: Use rq in idle_cpu

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Date: Thu, 4 Jan 2024 10:45:43 +0530
From: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
To: Pierre Gondois <pierre.gondois@....com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira
 <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] sched/fair: Use rq in idle_cpu_without()



On 1/3/24 6:26 PM, Pierre Gondois wrote:
> idle_cpu_without() could receive a 'struct rq' instead of a
> cpu number to avoid converting the cpu number to a 'struct rq'

nit: s/cpu/CPU

> two times. Indeed update_sg_wakeup_stats() already makes the
> conversion.

This change looks good. There maybe other candidates which might get simplified 
as well. for example, update_blocked_averages. (and then there are some 
like balance_push_set which maybe borderline when it comes to such simplification)

> 
> Signed-off-by: Pierre Gondois <pierre.gondois@....com>
> ---
>  kernel/sched/fair.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 93e928e76959..d38fec26fd3d 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -10184,15 +10184,13 @@ static unsigned int task_running_on_cpu(int cpu, struct task_struct *p)
>  
>  /**
>   * idle_cpu_without - would a given CPU be idle without p ?
> - * @cpu: the processor on which idleness is tested.
> + * @rq: the rq on which idleness is tested.
>   * @p: task which should be ignored.
>   *
>   * Return: 1 if the CPU would be idle. 0 otherwise.
>   */
> -static int idle_cpu_without(int cpu, struct task_struct *p)
> +static int idle_cpu_without(struct rq *rq, struct task_struct *p)

This might need change in the function name too. perception here is that, is the 
CPU idle without task p. 
Otherwise LGTM. 

Reviewed-by: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>

>  {
> -	struct rq *rq = cpu_rq(cpu);
> -
>  	if (rq->curr != rq->idle && rq->curr != p)
>  		return 0;
>  
> @@ -10247,7 +10245,7 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
>  		/*
>  		 * No need to call idle_cpu_without() if nr_running is not 0
>  		 */
> -		if (!nr_running && idle_cpu_without(i, p))
> +		if (!nr_running && idle_cpu_without(rq, p))
>  			sgs->idle_cpus++;
>  
>  		/* Check if task fits in the CPU */