linux-kernel - Re: [PATCH v2] tick/broadcast: Do not set oneshot_mask except was

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Date:   Thu, 4 May 2023 00:27:01 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Victor Hassan <victor@...winnertech.com>, fweisbec@...il.com,
        mingo@...nel.org, jindong.yue@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tick/broadcast: Do not set oneshot_mask except
 was_periodic was true

On Tue, May 02, 2023 at 02:38:57PM +0200, Thomas Gleixner wrote:
> Updated patch below.
> 
> Thanks,

Looks good from my layperson's eyes, just a doubt about a comment below:

> +
> +	/*
> +	 * When switching from periodic to oneshot mode arm the broadcast
> +	 * device for the next tick.
> +	 *
> +	 * If the broadcast device has been replaced in oneshot mode and
> +	 * the oneshot broadcast mask is not empty, then arm it to expire
> +	 * immediately in order to reevaluate the next expiring timer.
> +	 * nexttick is 0 and therefore in the past which will cause the

Is nexttick really in the past? It's set to tick_next_period...

Thanks.

> +	 * clockevent code to force an event.
> +	 *
> +	 * For both cases the programming can be avoided when the oneshot
> +	 * broadcast mask is empty.
> +	 *
> +	 * tick_broadcast_set_event() implicitly switches the broadcast
> +	 * device to oneshot state.
> +	 */
> +	if (!cpumask_empty(tick_broadcast_oneshot_mask))
> +		tick_broadcast_set_event(bc, cpu, nexttick);
>  }