linux-kernel - Re: [PATCH v5 6/6] timers: Exclude isolated cpus from timer migation

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Message-ID: <aCyVIfD-pbOlvsFy@localhost.localdomain>
Date: Tue, 20 May 2025 16:43:45 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Gabriele Monaco <gmonaco@...hat.com>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v5 6/6] timers: Exclude isolated cpus from timer migation

Le Thu, May 08, 2025 at 04:53:26PM +0200, Gabriele Monaco a écrit :
> diff --git a/kernel/time/timer_migration.c b/kernel/time/timer_migration.c
> index 25439f961ccf..fb27e929e2cf 100644
> --- a/kernel/time/timer_migration.c
> +++ b/kernel/time/timer_migration.c
> @@ -10,6 +10,7 @@
>  #include <linux/spinlock.h>
>  #include <linux/timerqueue.h>
>  #include <trace/events/ipi.h>
> +#include <linux/sched/isolation.h>
>  
>  #include "timer_migration.h"
>  #include "tick-internal.h"
> @@ -1478,6 +1479,16 @@ static int tmigr_cpu_available(unsigned int cpu)
>  	if (WARN_ON_ONCE(!tmc->tmgroup))
>  		return -EINVAL;
>  
> +	/*
> +	 * Domain isolated CPUs don't participate in timer migration.
> +	 * Checking here guarantees that CPUs isolated at boot (e.g. isolcpus)
> +	 * are not marked as available when they first become online.
> +	 * During runtime, any offline isolated CPU is also not incorrectly
> +	 * marked as available once it gets back online.
> +	 */
> +	if (!housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
> +	    cpuset_cpu_is_isolated(cpu))

if (housekeeping_cpu(cpu, HK_TYPE_KERNEL_NOISE) &&
    (!housekeeping_cpu(cpu,HK_TYPE_DOMAIN) || cpuset_cpu_is_isolated(cpu)))

Because nohz_full= must be part of the hierarchy.

> +		return 0;
>  	raw_spin_lock_irq(&tmc->lock);
>  	trace_tmigr_cpu_available(tmc);
>  	tmc->idle = timer_base_is_idle();
> @@ -1489,6 +1500,38 @@ static int tmigr_cpu_available(unsigned int cpu)
>  	return 0;
>  }
>  
> +static void tmigr_remote_cpu_unavailable(void *ignored)
> +{
> +	tmigr_cpu_unavailable(smp_processor_id());
> +}
> +
> +static void tmigr_remote_cpu_available(void *ignored)
> +{
> +	tmigr_cpu_available(smp_processor_id());
> +}
> +
> +int tmigr_isolated_exclude_cpumask(cpumask_var_t exclude_cpumask)
> +{
> +	cpumask_var_t cpumask;
> +	int ret = 0;
> +
> +	lockdep_assert_cpus_held();
> +
> +	if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
> +		return -ENOMEM;
> +
> +	cpumask_and(cpumask, exclude_cpumask, tmigr_available_cpumask);
> +	cpumask_and(cpumask, cpumask, housekeeping_cpumask(HK_TYPE_TICK));

Good, but please use HK_TYPE_KERNEL_NOISE, I need to finish that rename at some
point.

Thanks.

> +	on_each_cpu_mask(cpumask, tmigr_remote_cpu_unavailable, NULL, 0);
> +
> +	cpumask_andnot(cpumask, cpu_online_mask, exclude_cpumask);
> +	cpumask_andnot(cpumask, cpumask, tmigr_available_cpumask);
> +	on_each_cpu_mask(cpumask, tmigr_remote_cpu_available, NULL, 0);
> +
> +	free_cpumask_var(cpumask);
> +	return ret;
> +}
> +
>  static void tmigr_init_group(struct tmigr_group *group, unsigned int lvl,
>  			     int node)
>  {
> -- 
> 2.49.0
> 

-- 
Frederic Weisbecker
SUSE Labs