Re: Increased ipw2200 power usage with dynticks

[Bill Davidsen <davidsen@tmr.com>]

Björn Steinbrink wrote:
> On 2007.05.20 20:55:35 +0200, Andi Kleen wrote:
> > Björn Steinbrink <B.Steinbrink@gmx.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@tmr.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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