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Message-ID: <ZdN8KCTB2smSZb88@localhost.localdomain>
Date: Mon, 19 Feb 2024 17:04:56 +0100
From: Frederic Weisbecker <frederic@...nel.org>
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>,
Rik van Riel <riel@...riel.com>,
Steven Rostedt <rostedt@...dmis.org>,
Sebastian Siewior <bigeasy@...utronix.de>,
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>,
Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH v10 13/20] timers: Add get next timer interrupt
functionality for remote CPUs
Le Mon, Jan 15, 2024 at 03:37:36PM +0100, Anna-Maria Behnsen a écrit :
> +# ifdef CONFIG_SMP
> +/**
> + * fetch_next_timer_interrupt_remote() - Store next timers into @tevt
> + * @basej: base time jiffies
> + * @basem: base time clock monotonic
> + * @tevt: Pointer to the storage for the expiry values
> + * @cpu: Remote CPU
> + *
> + * Stores the next pending local and global timer expiry values in the
> + * struct pointed to by @tevt. If a queue is empty the corresponding
> + * field is set to KTIME_MAX. If local event expires before global
> + * event, global event is set to KTIME_MAX as well.
> + *
> + * Caller needs to make sure timer base locks are held (use
> + * timer_lock_remote_bases() for this purpose).
> + */
> +void fetch_next_timer_interrupt_remote(unsigned long basej, u64 basem,
> + struct timer_events *tevt,
> + unsigned int cpu)
> +{
> + struct timer_base *base_local, *base_global;
> +
> + /* Preset local / global events */
> + tevt->local = tevt->global = KTIME_MAX;
> +
> + base_local = per_cpu_ptr(&timer_bases[BASE_LOCAL], cpu);
> + base_global = per_cpu_ptr(&timer_bases[BASE_GLOBAL], cpu);
> +
> + lockdep_assert_held(&base_local->lock);
> + lockdep_assert_held(&base_global->lock);
> +
> + fetch_next_timer_interrupt(basej, basem, base_local, base_global, tevt);
If the next timer is global and it is <= jiffies + 1, the result will be
returned in tevt.local only and not on tevt.global. So a remote fetch may miss it.
For this to work on both local and remote fetch, you may need:
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 320eb4ceafa2..64ce9a7760f5 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -2004,6 +2007,8 @@ static unsigned long fetch_next_timer_interrupt(unsigned long basej, u64 basem,
if (time_before(nextevt, basej))
nextevt = basej;
tevt->local = basem + (u64)(nextevt - basej) * TICK_NSEC;
+ if (!local_first)
+ tevt->global = tevt->local;
return nextevt;
}
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