linux-kernel - Re: [PATCH] RFC: sched: Rework task_sched_runtime to avoid calling update_rq

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Date: Thu, 13 Jun 2024 12:51:42 +0100
From: Qais Yousef <qyousef@...alina.io>
To: Peter Zijlstra <peterz@...radead.org>
Cc: John Stultz <jstultz@...gle.com>, LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Ingo Molnar <mingo@...hat.com>, 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>,
	Joel Fernandes <joel@...lfernandes.org>, kernel-team@...roid.com
Subject: Re: [PATCH] RFC: sched: Rework task_sched_runtime to avoid calling
 update_rq_clock

On 06/13/24 12:04, Peter Zijlstra wrote:

> ---
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 0935f9d4bb7b..d4b87539d72a 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -724,7 +724,6 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
>  
>  	rq->prev_irq_time += irq_delta;
>  	delta -= irq_delta;
> -	psi_account_irqtime(rq->curr, irq_delta);
>  	delayacct_irq(rq->curr, irq_delta);
>  #endif
>  #ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING
> @@ -5459,6 +5458,8 @@ void sched_tick(void)
>  
>  	sched_clock_tick();
>  
> +	psi_account_irqtime(curr, &rq->psi_irq_time);
> +

If wakeup preemption causes a context switch, wouldn't we lose this
information then? I *think* active migration might cause this information to be
lost too.

pick_next_task() might be a better place to do the accounting?

>  	rq_lock(rq, &rf);
>  
>  	update_rq_clock(rq);