Re: [PATCH v10 20/20] timers: Always queue timers on the local CPU

Frederic Weisbecker
2024-02-01T17:36:07Z

Le Mon, Jan 15, 2024 at 03:37:43PM +0100, Anna-Maria Behnsen a écrit :
> The timer pull model is in place so we can remove the heuristics which try
> to guess the best target CPU at enqueue/modification time.
>
> All non pinned timers are queued on the local CPU in the separate storage
> and eventually pulled at expiry time to a remote CPU.
>
> Originally-by: Richard Cochran (linutronix GmbH) <richardcochran@gmail.com>
> Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

Just one detail below:

> @@ -590,10 +590,13 @@ trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
>
> /*
> * We might have to IPI the remote CPU if the base is idle and the
> - * timer is not deferrable. If the other CPU is on the way to idle
> - * then it can't set base->is_idle as we hold the base lock:
> + * timer is pinned. If it is a non pinned timer, it is only queued
> + * on the remote CPU, when timer was running during queueing. Then
> + * everything is handled by remote CPU anyway. If the other CPU is
> + * on the way to idle then it can't set base->is_idle as we hold
> + * the base lock:
> */
> - if (base->is_idle)
> + if (base->is_idle && timer->flags & TIMER_PINNED)

Is the TIMER_PINNED test necessary? If base->is_idle, then the timer
is now guaranteed to be TIMER_PINNED, right?

Thanks.