Subject: Re: high power consumption in recent kernels
From: Peter Zijlstra <peterz@infradead.org>
To: Norbert Preining <preining@logic.at>
Cc: Arjan van de Ven <arjan@infradead.org>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>, akpm <akpm@linux-foundation.org>,
       Mike Galbraith <efault@gmx.de>, tglx <tglx@linutronix.de>
In-Reply-To: <20100708124627.GA7754@gamma.logic.tuwien.ac.at>
References: <20100706164539.GA14783@gamma.logic.tuwien.ac.at>
	 <1278579992.1900.17.camel@laptop> <20100708045711.398d4e26@infradead.org>
	 <1278590303.1900.91.camel@laptop>
	 <20100708120421.GF20841@gamma.logic.tuwien.ac.at>
	 <1278591779.1900.97.camel@laptop>
	 <20100708124627.GA7754@gamma.logic.tuwien.ac.at>
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Date: Thu, 08 Jul 2010 15:23:46 +0200
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On Thu, 2010-07-08 at 21:46 +0900, Norbert Preining wrote:
> Looks promising, reverting the old patch, adding that one, building,
> running, unplugging ppower, powertop runs now since some time,
> it seems that we are back to better situation: 

Hrmm, Mike seems you wrecked power usage.. 

So nohz_ratelimit() prevents us from entering NOHZ when the last attempt
was less than 1/2 a jiffy ago (fwiw: NSEC_PER_SEC/HZ == TICK_NSEC).

Its either entering idle or irq_exit trying to enter nohz state, if we
keep skipping it it means that we get enough interrupt activity to
render nohz useless anyway.. so not quite sure how this wrecks things..
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