linux-kernel - Re: [PATCH] hrtimer: select housekeeping CPU during migration

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Date: Tue, 13 Feb 2024 13:36:40 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Costa Shulyupin <costa.shul@...hat.com>, Waiman Long
 <longman@...hat.com>, linux-kernel@...r.kernel.org
Cc: Frederic Weisbecker <frederic@...nel.org>
Subject: Re: [PATCH] hrtimer: select housekeeping CPU during migration

On Sun, Feb 11 2024 at 15:52, Costa Shulyupin wrote:
> because during CPU deactivation a timer can migrate
> to isolated CPU and break CPU isolation.

That's not a sentence.

> For reference see function get_nohz_timer_target,

get_nohz_timer_target()

> which selects CPU for new timers from
> housekeeping_cpumask(HK_TYPE_TIMER)

But what is the point of this statement?

> Inspired by Waiman Long <longman@...hat.com>

Can you please use a proper tag, i.e. Suggested-by and not invent some
random free form text just because?

> Signed-off-by: Costa Shulyupin <costa.shul@...hat.com>
> ---
>  kernel/time/hrtimer.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index f82997cf53b6..460d916e24b7 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -2227,7 +2227,7 @@ static void migrate_hrtimer_list(struct hrtimer_clock_base *old_base,
>  int hrtimers_cpu_dying(unsigned int dying_cpu)
>  {
>  	struct hrtimer_cpu_base *old_base, *new_base;
> -	int i, ncpu = cpumask_first(cpu_active_mask);
> +	int i, ncpu = cpumask_any_and(cpu_active_mask, housekeeping(HK_TYPE_TIMER));
>  	pr_debug("ncpu=%d, dying_cpu=%d\n", ncpu, dying_cpu);
>  
>  	tick_cancel_sched_timer(dying_cpu);

Q: Against which tree is this supposed to apply?

A: Against some private tree of yours which added the pr_debug() in a
   previous commit.

Can you please read and follow Documentation/process/ and provide
patches which actually can be applied without fixing them up manually?

Thanks,

        tglx