lowest C-state changes

[Volodymyr Kostyrko]

Любомир Григоров wrote:
>  > Have you checked http://wiki.freebsd.org/TuningPowerConsumption?
> I have. It was kind of confusing and didn't know about:
>  > 1. For CX states to function correctly you better disable throttling
>  > and powerd. I also witnessed at least one machine that hitting any CX
>  > mode stops generate interrupts on APIC clock (I had to boot it with a
>  > mousee until I disabled APIC clocks).
> So do you recommend I use throttling or C3? I think C3 runs slightly
> cooler. I can't tell since I don't drop under 50C in X. Fan increases at
> 60C and drops me back.

I wouldn't dare to recommend any particular configuration. Most times 
throttling is safer and with CX states you can get cooler. But both of 
them doesn't play nice together. If you want higher cooling you can try 
to disable throttling (and you will not need powerd as powerd takes care 
of frequencies) and enable CX but you will need to test everything 
thoroughly as unepected bugs can show up. Remember, the default way 
isn't the better one, just the safer one.

>  > First need to see what state the processor supports the current
>  > system
>  >sysctl -a | grep cx_
> This is before heavy load while it still remembers the C3:

It's just about ability to set C3 or any other particular state. Some 
processors show only C1 state as available.

For example:

 > sysctl hw.model
hw.model: Intel(R) Core(TM)2 Duo CPU     E8400  @ 3.00GHz
 > sysctl dev.cpu | grep cx
dev.cpu.0.cx_supported: C1/1
dev.cpu.0.cx_lowest: C1
dev.cpu.0.cx_usage: 100.00% last 293us
dev.cpu.1.cx_supported: C1/1
dev.cpu.1.cx_lowest: C1
dev.cpu.1.cx_usage: 100.00% last 15us

Setting lower CX on this machine results in:

# sysctl hw.acpi.cpu.cx_lowest=C3
hw.acpi.cpu.cx_lowest: C1
sysctl: hw.acpi.cpu.cx_lowest: Invalid argument

-- 
Sphinx of black quartz judge my vow.