linux-kernel - Re: [PATCH] irq_work: Replace wait loop with rcuwait_wait

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Message-ID: <ZvHghxL6ce-2y7Wx@pavilion.home>
Date: Mon, 23 Sep 2024 23:41:27 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Steven Davis <goldside000@...look.com>
Cc: akpm@...ux-foundation.org, ankur.a.arora@...cle.com,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	tglx@...utronix.de
Subject: Re: [PATCH] irq_work: Replace wait loop with rcuwait_wait_event

Le Thu, Sep 19, 2024 at 11:43:26AM -0400, Steven Davis a écrit :
> The previous implementation of irq_work_sync used a busy-wait
> loop with cpu_relax() to check the status of IRQ work. This
> approach, while functional, could lead to inefficiencies in
> CPU usage.
> 
> This commit replaces the busy-wait loop with the rcuwait_wait_event
> mechanism. This change leverages the RCU wait mechanism to handle
> waiting for IRQ work completion more efficiently, improving CPU
> responsiveness and reducing unnecessary CPU usage.
> 
> Signed-off-by: Steven Davis <goldside000@...look.com>
> ---
>  kernel/irq_work.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 2f4fb336dda1..2b092a1d07a9 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -295,8 +295,7 @@ void irq_work_sync(struct irq_work *work)
>  		return;
>  	}
>  
> -	while (irq_work_is_busy(work))
> -		cpu_relax();
> +	rcuwait_wait_event(&work->irqwait, !irq_work_is_busy(work), TASK_UNINTERRUPTIBLE);

So you can remove the CONFIG_PREEMPT_RT special case in this function, right?

Thanks.

>  }
>  EXPORT_SYMBOL_GPL(irq_work_sync);
>  
> -- 
> 2.39.5
>