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

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Date:	Tue, 22 May 2007 13:43:29 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Björn Steinbrink <B.Steinbrink@....de>,
	Andi Kleen <andi@...stfloor.org>, 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

Björn Steinbrink wrote:
> 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 :)
> 
Very encouraging, hopefully that can get into mainline soon, as power 
usage is an issue with laptops. Until then, it sounds as if dynticks is 
a negative power save for ipw2200 (and probably many other things).

Dare we hope that this will allow use of USB on laptops without draining 
the battery?

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

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