linux-kernel - Re: Increased ipw2200 power usage with dynticks

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Date:	Mon, 21 May 2007 09:49:38 +0200
From:	Björn Steinbrink <B.Steinbrink@....de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	tglx@...utronix.de, mingo@...e.hu, yi.zhu@...el.com,
	linux-kernel@...r.kernel.org, arjan@...radead.org,
	venkatesh.pallipadi@...el.com, trenn@...e.de
Subject: Re: Increased ipw2200 power usage with dynticks

On 2007.05.20 20:55:35 +0200, Andi Kleen wrote:
> Björn Steinbrink <B.Steinbrink@....de> writes:
> > 
> > Ok, it seems that ipw2200 is just a trigger for the problem here. AFAICT
> > the cause of the worse C state usage is that after ipw2200 has woken the
> > cpu, acpi_processor_idle() chooses C2 (due to dma? bm? I have no
> > idea...) as the prefered sleep state. Now without NO_HZ or when I hold
> > down a key, there are interrupts that wake up the CPU and when
> > acpi_processor_idle() is called again the promotion to C3/C4 happens.
> > But with NO_HZ, there are no such interrupts, most wakeups are caused by
> > ipw2200 and so the processor doesn't go any deeper than C2 most of the
> > time and thus wastes lots of power.
> 
> The cpuidle governour code Venki is working on is supposed to address this.
> There have been also earlier prototype patches by Adam Belay and
> Thomas Renninger.

Venki (at least I think it was him) also told me about cpuidle and the
menu governor on #powertop. Unfortunately, cpuidle seems to be gone from
acpi-test (or I'm simply still too stupid for git/gitweb). I manually
added the cpuidle and menu governor patches on top of my 2.6.22-rc1-hrt8
kernel, but that broke C-state duration accounting.

On the bright side of things is power usage though, which is down to an
incredible 13.9W in idle+ipw2200 :)

Thanks,
Björn

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