linux-kernel - Re: [PATCH v2 0/2] new cpumask for hotpluggable CPUs

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Message-ID: <1313091519.8491.31.camel@twins>
Date:	Thu, 11 Aug 2011 21:38:39 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Turquette, Mike" <mturquette@...com>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	linaro-dev@...ts.linaro.org, patches@...aro.org, gregkh@...e.de
Subject: Re: [PATCH v2 0/2] new cpumask for hotpluggable CPUs

On Thu, 2011-08-11 at 12:25 -0700, Turquette, Mike wrote:
> On Thu, Aug 11, 2011 at 11:30 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Wed, 2011-08-10 at 13:03 -0700, Mike Turquette wrote:
> >> This patch series introduces a new cpumask which tracks CPUs that
> >> support hotplugging.  The purpose of this patch series is to provide a
> >> simple method for kernel code to know which CPUs can be hotplugged and
> >> which ones cannot.  Potential users of this code might be a thermal
> >> mitigation technique which uses hotplug to lower temperature, or a power
> >> capping mechanism which uses hotplug to lower power consumption.
> >>
> >> All the of usual cpumask helper functions are created for this new mask.
> >> The second patch in this series simply sets the bit for elligible CPUs
> >> while they are being registered.  The cpumask itself is static after
> >> boot and should not change (like the possbile mask).
> >
> > I still most strongly object to people using hotplug for these goals.
> >
> > Why do you need to go through the entire dance of hotplug just to idle a
> > cpu? Hotplug not only idles the cpu but tears down (and rebuilds) an
> > insane amount of resources associated with the cpu.
> 
> I think you're nacking the wrong series.  This patchset simply allows
> kernel space to know which CPUs can go offline and which one can't,
> which seems pretty innocuous.  Are you fundamentally opposed to the
> kernel having better accessor functions to this data?

Yeah, people might think its sane to use it..

> I'll soon be posting some code which does implement hotplug as a
> power-capping feature.  I think *that* is the patch that you'll want
> to nack.

That too of course..
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