linux-kernel - Re: A few questions and issues with dynticks, NOHZ and powertop

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Message-ID: <4BBA0E74.2090803@linux.intel.com>
Date:	Mon, 05 Apr 2010 09:23:16 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Dominik Brodowski <linux@...inikbrodowski.net>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Dmitry Torokhov <dtor@...l.ru>
Subject: Re: A few questions and issues with dynticks, NOHZ and powertop

On 4/5/2010 9:22, Paul E. McKenney wrote:
> On Mon, Apr 05, 2010 at 09:07:33AM -0700, Arjan van de Ven wrote:
>> On 4/5/2010 8:14, Paul E. McKenney wrote:
>>> So the main issue is that for many workloads, it is best to run full bore
>>> and get done quickly, thus allowing the entire machine to be powered down?
>>
>> yep
>>
>>> If so, it seems likely that there would be some workloads that were sometimes
>>> unable to use all the CPUs, in which case shutting down (idling, offlining,
>>> dyntick-idling, whatever) the excess CPUs might nevertheless be the right
>>> thing to do.
>>
>> but the point is that the normal scheduler + idle behavior gives you exactly that
>> in a natural way !
>> If you don't have enough work (tasks) to keep all cores busy, the others are and stay idle.
>
> So your earlier objection was not to dyntick-idle as such, but rather
> to artificially constraining the scheduler to induce dyntick-idle?

my objection was against the notion that offlining cpus helps power/energy ;-)

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