linux-kernel - Re: [PATCH v2 1/2] cpumask: introduce cpumask for hotpluggable CPUs

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Message-ID: <4E42EFCB.1030005@linaro.org>
Date:	Wed, 10 Aug 2011 22:53:31 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Mike Turquette <mturquette@...com>
CC:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	gregkh@...e.de, linaro-dev@...ts.linaro.org, patches@...aro.org
Subject: Re: [PATCH v2 1/2] cpumask: introduce cpumask for hotpluggable CPUs

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On 08/10/2011 10:03 PM, Mike Turquette wrote:
> On some platforms it is possible to have some CPUs which support CPU
> hotplug and some which do not.  Currently the prescence of an 'online'
> sysfs entry in userspace is adequate for applications to know that a CPU
> supports hotplug, but there is no convenient way to make the same
> determination in the kernel.
> 
> To better model this relationship this patch introduces a new cpumask to
> track CPUs that support CPU hotplug operations.
> 
> This new cpumask is populated at boot-time and remains static for the
> life of the machine.  Bits set in the mask indicate a CPU which supports
> hotplug, but make no guarantees about whether that CPU is currently
> online or not.  Likewise a cleared bit in the mask indicates either a
> CPU which cannot hotplug or a lack of a populated CPU.
> 
> The purpose of this new cpumask is to aid kernel code which uses CPU to
> take CPUs online and offline.  Possible uses are as a thermal event
> mitigation technique or as a power capping mechanism.
> 
> Signed-off-by: Mike Turquette <mturquette@...com>

Reviewed-by: Daniel Lezcano <daniel.lezcano@...aro.org>

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