linux-kernel - Re: [PATCH v5 1/2] smpboot: allow excluding cpus from the smpboot threads

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Date:	Wed, 8 Apr 2015 15:28:57 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	cmetcalf@...hip.com
Cc:	Don Zickus <dzickus@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrew Jones <drjones@...hat.com>,
	chai wen <chaiw.fnst@...fujitsu.com>,
	Ulrich Obergfell <uobergfe@...hat.com>,
	Fabian Frederick <fabf@...net.be>,
	Aaron Tomlin <atomlin@...hat.com>,
	Ben Zhang <benzh@...omium.org>,
	Christoph Lameter <cl@...ux.com>,
	Gilad Ben-Yossef <gilad@...yossef.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	linux-doc@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v5 1/2] smpboot: allow excluding cpus from the smpboot
 threads

On Mon, Apr 06, 2015 at 03:45:55PM -0400, cmetcalf@...hip.com wrote:
> From: Chris Metcalf <cmetcalf@...hip.com>
> 
> This change allows some cores to be excluded from running the
> smp_hotplug_thread tasks.  The motivating example for this is
> the watchdog threads, which by default we don't want to run
> on any enabled nohz_full cores.
> 
> Signed-off-by: Chris Metcalf <cmetcalf@...hip.com>
> ---
>  include/linux/smpboot.h |  2 ++
>  kernel/smpboot.c        | 11 ++++++++---
>  2 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/smpboot.h b/include/linux/smpboot.h
> index d600afb21926..de2f64a98108 100644
> --- a/include/linux/smpboot.h
> +++ b/include/linux/smpboot.h
> @@ -27,6 +27,7 @@ struct smpboot_thread_data;
>   * @pre_unpark:		Optional unpark function, called before the thread is
>   *			unparked (cpu online). This is not guaranteed to be
>   *			called on the target cpu of the thread. Careful!
> + * @exclude_mask:	Optional cpumask, specifying cores to exclude.
>   * @selfparking:	Thread is not parked by the park function.
>   * @thread_comm:	The base name of the thread
>   */
> @@ -41,6 +42,7 @@ struct smp_hotplug_thread {
>  	void				(*park)(unsigned int cpu);
>  	void				(*unpark)(unsigned int cpu);
>  	void				(*pre_unpark)(unsigned int cpu);
> +	cpumask_t			*exclude_mask;

The usual pattern for cpumasks is to use them as affinity values instead
of non-affinity values.

Thanks.
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