linux-kernel - Re: [RFC patch V2 2/7] kthread: Implement park/unpark facility

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Date:	Mon, 18 Jun 2012 17:43:41 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [RFC patch V2 2/7] kthread: Implement park/unpark facility

On Fri, 15 Jun 2012 14:13:21 -0000, Thomas Gleixner wrote:
> To avoid the full teardown/setup of per cpu kthreads in the case of
> cpu hot(un)plug, provide a facility which allows to put the kthread
> into a park position and unpark it when the cpu comes online again.
>

Please see a comment below. Other than that, you can add my

  Reviewed-by: Namhyung Kim <namhyung@...nel.org>

if you want.


> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/kthread.h |   11 ++
>  kernel/kthread.c        |  184 +++++++++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 175 insertions(+), 20 deletions(-)
[snip]
>  /**
> + * kthread_create_on_cpu - Create a cpu bound kthread
> + * @threadfn: the function to run until signal_pending(current).
> + * @data: data ptr for @threadfn.
> + * @cpu: The cpu on which the thread should be bound,
> + * @namefmt: printf-style name for the thread.

How about adding a comment that @namefmt can handle a single %u only
for the cpu number in the current implementation?

Thanks,
Namhyung


> + *
> + * Description: This helper function creates and names a kernel thread
> + * The thread will be woken and put into park mode.
> + */
> +struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
> +					  void *data, unsigned int cpu,
> +					  const char *namefmt)
> +{
> +	struct task_struct *p;
> +
> +	p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
> +				   cpu);
> +	if (IS_ERR(p))
> +		return p;
> +	set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
> +	to_kthread(p)->cpu = cpu;
> +	/* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
> +	kthread_park(p);
> +	return p;
> +}
> +
--
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