Re: Is the C3 possible with SMP?

On Mon, 2008-11-03 at 00:06 +0200, Alexander Motin wrote:
> Alexandre "Sunny" Kovalenko wrote:
> >> I have tried to enable C3 state on my Core2Duo laptop and found that it 
> >> is not working good. System HZ timer stops during CPU sleep. After some 
> >> investigation I have found that it is due to LAPIC timer used for HZ 
> >> stopped during C3 state (same as during AMD's C1E).
> >>
> >> So the question is: Is it possible (or planned) to make it work somehow? 
> >> For example, by using some external timer instead of LAPIC's one?
> >>
> >> ACPI reports about 20% less idle power consumption with C3 state 
> >> comparing to C2. It would be interesting to get additional half an hour 
> >> on battery.
> >>
> > You can get half way there by adding
> > 
> > dev.cpu.1.cx_lowest=C3
> > 
> > to /etc/sysctl.conf
> 
> Thanks.
> 
> 1. Looks like it does not kill the timer.
> 2. I haven't got any benefit from it in idle state. According to 
> `acpiconf -i 0` I have about 13 Amps (IMHO more looks like Watts) with 
> both C2 and this half-to-C3, but only 11 Amps in full C3 (but without 
> timer).
> 3. I have got about 10% benefit (33 Amps against 36) when cpu0 is 100% 
> busy while cpu1 is idle.
> 
You would not happen to have USB loaded or built into kernel? If you do,
you will practically never go into C3. What does

sysctl dev.cpu | grep cx_usage 

say?

-- 
Alexandre "Sunny" Kovalenko (Олександр Коваленко)

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