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Date:   Mon, 9 Oct 2023 23:15:27 +0200
From:   Frederic Weisbecker <frederic@kernel.org>
To:     Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc:     linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        John Stultz <jstultz@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Eric Dumazet <edumazet@google.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Arjan van de Ven <arjan@infradead.org>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Rik van Riel <riel@surriel.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Sebastian Siewior <bigeasy@linutronix.de>,
        Giovanni Gherdovich <ggherdovich@suse.cz>,
        Lukasz Luba <lukasz.luba@arm.com>,
        "Gautham R . Shenoy" <gautham.shenoy@amd.com>,
        Srinivas Pandruvada <srinivas.pandruvada@intel.com>,
        K Prateek Nayak <kprateek.nayak@amd.com>
Subject: Re: [PATCH v8 09/25] timer: Split out get next timer functionality
Message-ID: <ZSRtb9Kh-m0laSwL@localhost.localdomain>
References: <20231004123454.15691-1-anna-maria@linutronix.de>
 <20231004123454.15691-10-anna-maria@linutronix.de>
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Le Wed, Oct 04, 2023 at 02:34:38PM +0200, Anna-Maria Behnsen a ?crit :
> Split out get next timer functionality to make it reusable in other
> places. Thereby the order of getting the next expiry, forwarding the base
> clock and mark timer bases as idle, is changed. This change of order
> shouldn't have any impact, as nothing inside the function relies on the
> idle value or the updated timer base clock.
> 
> Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
> ---
>  kernel/time/timer.c | 30 +++++++++++++++++++++---------
>  1 file changed, 21 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 18f8aac9b19a..f443aa807fbc 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
> @@ -1911,6 +1911,24 @@ static u64 cmp_next_hrtimer_event(u64 basem, u64 expires)
>  	return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC;
>  }
>  
> +static inline unsigned long __get_next_timer_interrupt(unsigned long basej,
> +						       struct timer_base *base)
> +{
> +	unsigned long nextevt;
> +
> +	if (base->next_expiry_recalc)
> +		next_expiry_recalc(base);
> +	nextevt = base->next_expiry;
> +
> +	if (base->timers_pending) {
> +		/* If we missed a tick already, force 0 delta */
> +		if (time_before(nextevt, basej))
> +			nextevt = basej;
> +	}
> +
> +	return nextevt;
> +}
> +
>  /**
>   * get_next_timer_interrupt - return the time (clock mono) of the next timer
>   * @basej:	base time jiffies
> @@ -1933,9 +1951,7 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
>  		return expires;
>  
>  	raw_spin_lock(&base->lock);
> -	if (base->next_expiry_recalc)
> -		next_expiry_recalc(base);
> -	nextevt = base->next_expiry;
> +	nextevt = __get_next_timer_interrupt(basej, base);
>  
>  	/*
>  	 * We have a fresh next event. Check whether we can forward the
> @@ -1952,14 +1968,10 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem)
>  	 */
>  	base->is_idle = time_after(nextevt, basej + 1);
>  
> -	if (base->timers_pending) {
> -		/* If we missed a tick already, force 0 delta */
> -		if (time_before(nextevt, basej))
> -			nextevt = basej;
> -		expires = basem + (u64)(nextevt - basej) * TICK_NSEC;
> -	}
>  	raw_spin_unlock(&base->lock);
>  
> +	expires = basem + (u64)(nextevt - basej) * TICK_NSEC;

Does that compute KTIME_MAX when there is no timers pending?

Thanks.

> +
>  	return cmp_next_hrtimer_event(basem, expires);
>  }
>  
> -- 
> 2.39.2
>