linux-kernel - Re: [RFC 2/4] timer: don't migrate pinned timers

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Message-ID: <7htxae5plh.fsf@paris.lan>
Date:	Mon, 31 Mar 2014 08:56:26 -0700
From:	Kevin Hilman <khilman@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	tglx@...utronix.de, fweisbec@...il.com, peterz@...radead.org,
	mingo@...nel.org, tj@...nel.org, lizefan@...wei.com,
	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org
Subject: Re: [RFC 2/4] timer: don't migrate pinned timers

Viresh Kumar <viresh.kumar@...aro.org> writes:

> migrate_timer() is called when a CPU goes down and its timers are required to be
> migrated to some other CPU. Its the responsibility of the users of the timer to
> remove it before control reaches to migrate_timers().
>
> As these were the pinned timers, the best we can do is: don't migrate these and
> report to the user as well.
>
> That's all this patch does.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  kernel/timer.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/kernel/timer.c b/kernel/timer.c
> index fec4ab4..a7f8b99 100644
> --- a/kernel/timer.c
> +++ b/kernel/timer.c
> @@ -1606,11 +1606,22 @@ static int init_timers_cpu(int cpu)
>  static void migrate_timer_list(struct tvec_base *new_base, struct list_head *head)
>  {
>  	struct timer_list *timer;
> +	int is_pinned;
>  
>  	while (!list_empty(head)) {
>  		timer = list_first_entry(head, struct timer_list, entry);
>  		/* We ignore the accounting on the dying cpu */
>  		detach_timer(timer, false);
> +
> +		is_pinned = tbase_get_pinned(timer->base);
> +
> +		/* Check if CPU still has pinned timers */
> +		if (is_pinned) {
> +			pr_warn("%s: can't migrate pinned timer: %p, removing it\n",
> +					__func__, timer);

printk message will be confusing: removing it from what? 

Kevin


> +			continue;
> +		}
> +
>  		timer_set_base(timer, new_base);
>  		internal_add_timer(new_base, timer);
>  	}
--
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