Is the C3 possible with SMP?

[martinko]

Alexandre "Sunny" Kovalenko wrote:
> 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?
> 

Hi,

My laptop reports C1 state only:

$ sysctl -a | grep cx_
hw.acpi.cpu.cx_lowest: C1
dev.cpu.0.cx_supported: C1/1
dev.cpu.0.cx_lowest: C1
dev.cpu.0.cx_usage: 100.00%

But this is Pentium-M and I remember it could use C2 and C3 back with 
5.x kernel and I'm sure I had USB as I have now.

Do you have any idea why I don't have C2/C3 states available anymore ??

Cheers,

Martin