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Date:   Tue, 27 Jun 2023 12:51:20 +0200
From:   Frederic Weisbecker <frederic@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Anna-Maria Behnsen <anna-maria@linutronix.de>,
        John Stultz <jstultz@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Eric Biederman <ebiederm@xmission.com>,
        Oleg Nesterov <oleg@redhat.com>
Subject: Re: [patch 12/45] posix-cpu-timers: Simplify posix_cpu_timer_set()
Message-ID: <ZJq/KHqjChLWtypG@lothringen>
References: <20230606132949.068951363@linutronix.de>
 <20230606142031.705286109@linutronix.de>
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On Tue, Jun 06, 2023 at 04:37:37PM +0200, Thomas Gleixner wrote:
> Avoid the late sighand lock/unlock dance when a timer is not armed to
> enforce reevaluation of the timer base so that the process wide CPU timer
> sampling can be disabled.
> 
> Do it right at the point where the arming decision is made which already
> has sighand locked.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  kernel/time/posix-cpu-timers.c |   38 +++++++++++++-------------------------
>  1 file changed, 13 insertions(+), 25 deletions(-)
> 
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -720,10 +720,14 @@ static int posix_cpu_timer_set(struct k_
>  	/*
>  	 * Arm the timer if it is not disabled, the new expiry value has
>  	 * not yet expired and the timer requires signal delivery.
> -	 * SIGEV_NONE timers are never armed.
> +	 * SIGEV_NONE timers are never armed. In case the timer is not
> +	 * armed, enforce the reevaluation of the timer base so that the
> +	 * process wide cputime counter can be disabled eventually.
>  	 */
>  	if (!sigev_none && new_expires && now < new_expires)
>  		arm_timer(timer, p);
> +	else
> +		trigger_base_recalc_expires(timer, p);

We don't need a recalc if sigev_none, right?

Thanks.

>  
>  	unlock_task_sighand(p, &flags);
>  	/*