Is the C3 possible with SMP?

[Kevin Oberman]

> From: martinko <gamato at users.sf.net>
> Date: Thu, 20 Nov 2008 22:32:57 +0100
> Sender: owner-freebsd-mobile at freebsd.org
> 
> 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 ??

Under 7-Stable, my Pentium-M system (ThinkPad T43) shows C1, C2, and
C3. Of course, it's not an SMP.
dev.cpu.0.cx_supported: C1/1 C2/1 C3/85
dev.cpu.0.cx_lowest: C1
dev.cpu.0.cx_usage: 100.00% 0.00% 0.00%

cx_supported has nothing to do with the value of cx_lowest. It should
simply be what the CPU reports back vi ACPI as to the C states supported
on the platform.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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