Re: Help! I lost my C4 states :-)

[Len Brown <len.brown-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On Mon, 2005-02-21 at 03:12, Stefan Seyfried wrote:
> Hi,
> 
> Just curious:
> i'm tracking Linus-bk-head quite closely. In (late?) January,
> i was able to get my DELL D600 into C4. It worked fine and it
> even got me an estimated 15-30 extra minutes out of the battery
> (usually it lasts ~3.5 hours, the projected time with C4 was more
> like almost 4 hours). Although this is great (it is more than i
> ever got from laptop_mode and spinning down the harddisk), it
> suddenly stopped working in February. Now the machine almost
> always stays in C2, it hardly enters C3 or C4.
> 
> seife@strolchi:~> cat /proc/acpi/processor/CPU0/power
> active state:            C2
> max_cstate:              C8
> bus master activity:     10000500
> states:
>     C1:                  type[C1] promotion[C2] demotion[--] latency[001] usage[00000010]
>    *C2:                  type[C2] promotion[C3] demotion[C1] latency[001] usage[107659165]
>     C3:                  type[C3] promotion[C4] demotion[C2] latency[085] usage[03505424]
>     C4:                  type[C3] promotion[--] demotion[C3] latency[185] usage[06231087]
> 
> There is always some bus master activity which i have not been able to track
> down. I tried unloading almost all modules, but it did not help. Of course
> there is no sound running, no USB mouse attached etc. I have quiesced the
> harddisk with laptop_mode and mounting filesystems noatime and commit=300.
> 
> The only thing that i can think of what has changed in my setup is that we
> changed to modular IDE device drivers, but i cannot really imagine how that
> would produce more bus master activity.
> 
> Any hints on how to track down what is causing bus master activity all the
> time?
> Has the calculation algorithm changed? Any default settings i could tweak?

Did you notice a battery life decrease with this decrease in C4
residency?

On January 20th we pushed Dominik's jiffies based bm_activity patch
in drivers/acpi/processor_idle.c  You might find that backing out
that file a couple of revisions restores the previous behaviour.

Just after that, I added a tunable that you can tweak --
with 1000 HZ, its default is all bits enabled, but
you can reduce this bit mask to make the driver
ignore less recent history:

# echo 0 > /sys/module/processor/parameters/bm_history

Will cause the processor driver to ignore the bus master activity
completely.  Note that this could cause a performance hit if
there is BM activity since will just pop the system out of C4
and no instructions are executed during the transition out of C4.

cheers,
-Len

ps.
If you're tracking battery life, I'd be interested to know if
you notice a difference between when you build with HZ=100 and HZ=1000.




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