linux-kernel - Re: [PATCH v2] tick: shift tick_nohz_switch_to_nohz() from tick_check_oneshot_change() to hrtimer_run

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Date: Mon, 03 Jun 2024 10:14:40 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>, Frederic Weisbecker
 <frederic@...nel.org>, Ingo Molnar <mingo@...nel.org>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tick: shift tick_nohz_switch_to_nohz() from
 tick_check_oneshot_change() to hrtimer_run_queues()

On Sun, Jun 02 2024 at 12:20, Oleg Nesterov wrote:
> @@ -1891,8 +1891,11 @@ void hrtimer_run_queues(void)
>  	 * there only sets the check bit in the tick_oneshot code,
>  	 * otherwise we might deadlock vs. xtime_lock.
>  	 */
> -	if (tick_check_oneshot_change(!hrtimer_is_hres_enabled())) {
> -		hrtimer_switch_to_hres();
> +	if (tick_check_oneshot_change()) {
> +		if (hrtimer_is_hres_enabled())
> +			hrtimer_switch_to_hres();
> +		else
> +			tick_nohz_switch_to_nohz();

hrtimers have no business with tick_nohz_switch_to_nohz(),
really. That's a strict tick/nohz specific thing. hrtimers do not care
about NOHZ much. They care about whether they can switch to high
resolution mode.

Thanks,

        tglx