linux-kernel - Re: [PATCH v9 24/32] timers: Split out "get next timer interrupt" functionality

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Message-ID: <20231206102057.RrJjegFf@linutronix.de>
Date:   Wed, 6 Dec 2023 11:20:57 +0100
From:   Sebastian Siewior <bigeasy@...utronix.de>
To:     Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <jstultz@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Eric Dumazet <edumazet@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Arjan van de Ven <arjan@...radead.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Lukasz Luba <lukasz.luba@....com>,
        "Gautham R . Shenoy" <gautham.shenoy@....com>,
        Srinivas Pandruvada <srinivas.pandruvada@...el.com>,
        K Prateek Nayak <kprateek.nayak@....com>
Subject: Re: [PATCH v9 24/32] timers: Split out "get next timer interrupt"
 functionality

On 2023-12-01 10:26:46 [+0100], Anna-Maria Behnsen wrote:
> diff --git a/kernel/time/timer.c b/kernel/time/timer.c
> index 0d53d853ae22..fc376e06980e 100644
> --- a/kernel/time/timer.c
> +++ b/kernel/time/timer.c
…
> +static inline u64 __get_next_timer_interrupt(unsigned long basej, u64 basem,
> +					     bool *idle)
> +{
> +	struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX };
> +	struct timer_base *base_local, *base_global;
> +	unsigned long nextevt;
> +	u64 expires;
> +
> +	/*
> +	 * Pretend that there is no timer pending if the cpu is offline.
> +	 * Possible pending timers will be migrated later to an active cpu.
> +	 */
> +	if (cpu_is_offline(smp_processor_id())) {
> +		if (idle)
> +			*idle = true;
> +		return tevt.local;
> +	}
> +
> +	base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]);
> +	base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]);
> +
> +	raw_spin_lock(&base_local->lock);
> +	raw_spin_lock_nested(&base_global->lock, SINGLE_DEPTH_NESTING);
> +
> +	nextevt = fetch_next_timer_interrupt(basej, basem, base_local,
> +					     base_global, &tevt);

Now you split it, move it and we have the __forward_timer_base() back in
case of the shortcut which is now in fetch_next_timer_interrupt().
All good.

>  
>  	/*
>  	 * We have a fresh next event. Check whether we can forward the

Sebastian