Re: Avoid C2/C3 idle state

Alex
2009-11-25T12:05:45Z

> > > Hey,
> > >
> > > you can set the maximum C-state to use using the
> > > "processor.max_cstate=<value>" parameter.
> No need to
> > > recompile.
> >
> > Thanks for your kind reply.
> >
> > A stupid qustion:
> > <value> is a numeric value as 1 , 2 , 3
> (i.e. processor.max_cstate=1 )
> > or is a string like C1 , C2 , C3 (i.e.
> processor.max_cstate=C1 ) ?
>
> It's the former. I'd suggest you try max_cstate=2 first, as
> that might save
> power, reduce heat and still not interfere with the serial
> device.

MMhh , there is a problem in my kernel 2.6.24 (Ubuntu 8.04.3 original)

[    0.000000] Kernel command line: root=UUID=27d1e179-62d3-4996-878e-e4a456bd45f4 ro quiet splash acpi=force processor.max_cstate=2
[    0.000000] Unknown boot option `processor.max_cstate=2': ignoring

This is a known problem related to Ubuntu 8.04, solved here:
http://www.inliniac.net/blog/2008/07/25/fixing-noise-on-ubuntu-hardy-804-aka-setting-max_cstate.html

Really my idea is that my serial problems are involved with C3 state: 800 microsec. latency and cache loss.
So I agree with your suggestion to use max_cstate=2.
But it doesn't work: serial overrun still there.
max_cstate=1 works fine : no overrun at all.
C2 state is buggy too.
I don't know if it's a hardware problem or acpi code problem, but with C1 it works fine and I'm happy :-)