Björn Steinbrink wrote:
On 2007.05.20 20:55:35 +0200, Andi Kleen wrote:
Björn Steinbrink <[email protected]> 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 <[email protected]>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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