Re: [PATCH v5 16/18] timer: Implement the hierarchical pull model

[Frederic Weisbecker <frederic@kernel.org>]

On Wed, Mar 01, 2023 at 03:17:42PM +0100, Anna-Maria Behnsen wrote:
> +static u64 tmigr_handle_remote_cpu(unsigned int cpu, u64 now,
> +				   unsigned long jif)
> +{
> +	struct timer_events tevt;
> +	struct tmigr_walk data;
> +	struct tmigr_cpu *tmc;
> +	u64 next = KTIME_MAX;
> +	unsigned long flags;
> +
> +	tmc = per_cpu_ptr(&tmigr_cpu, cpu);
> +
> +	raw_spin_lock_irqsave(&tmc->lock, flags);
> +	/*
> +	 * Remote CPU is offline or no longer idle or other cpu handles cpu
> +	 * timers already or next event was already expired - return!
> +	 */
> +	if (!tmc->online || tmc->remote || tmc->cpuevt.ignore ||
> +	    now < tmc->cpuevt.nextevt.expires) {
> +		raw_spin_unlock_irqrestore(&tmc->lock, flags);
> +		return next;
> +	}
> +
> +	tmc->remote = 1;
> +
> +	/* Drop the lock to allow the remote CPU to exit idle */
> +	raw_spin_unlock_irqrestore(&tmc->lock, flags);
> +
> +	if (cpu != smp_processor_id())
> +		timer_expire_remote(cpu);
> +
> +	/* next event of cpu */
> +	fetch_next_timer_interrupt_remote(jif, now, &tevt, cpu);

If the target CPU gets an idle interrupt right after the above call and enqueues
a new timer (which becomes the new earliest), tmigr_cpu_deactivate() ->
tmigr_new_timer() is going to ignore it due to tmc->remote = 1, right?

Or am I missing something else that would make that timer correctly handled?

Thanks.