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

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Date:	20 May 2007 20:55:35 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Björn Steinbrink <B.Steinbrink@....de>
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

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.

-Andi
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