C-States configuration

[Kevin Oberman]

On Wed, Apr 9, 2014 at 11:22 AM, hiren panchasara <
hiren.panchasara at gmail.com> wrote:

> On Wed, Apr 9, 2014 at 11:07 AM, Anton Sayetsky <vsjcfm at gmail.com> wrote:
> > 2014-04-09 20:40 GMT+03:00 hiren panchasara <hiren.panchasara at gmail.com
> >:
> >> I am running -current on my T420 at r263906M
> >>
> >> debug.acpi.acpi_ca_version: 20130823
> >>
> >> o/p of sysctl -a | grep acpi - http://bpaste.net/show/199806/
> >>
> >>  and I have following in my rc.conf:
> >>
> >> performance_cx_lowest="Cmax"
> >> economy_cx_lowest="Cmax"
> >>
> >> But I still get:
> >>
> >> % sysctl -a | grep cx_lowest
> >> hw.acpi.cpu.cx_lowest: C1
> >> dev.cpu.0.cx_lowest: C1
> >> dev.cpu.1.cx_lowest: C1
> >> dev.cpu.2.cx_lowest: C1
> >> dev.cpu.3.cx_lowest: C1
> >>
> >> And I can do:
> >> # sysctl dev.cpu.0.cx_lowest=Cmax
> >> dev.cpu.0.cx_lowest: C1 -> C8
> >>
> >> that tells me that Cmax is C8.
> >>
> >> % sysctl -d dev.cpu.0.cx_lowest
> >> dev.cpu.0.cx_lowest: lowest Cx sleep state to use
> >>
> >> I was expecting cx_lowest to be set to C8 because of rc.conf config I
> have.
> >>
> >> What am I missing here?
> >>
> >> cheers,
> >> Hiren
> > Try to set LOW instead of Cmax.
>
> I will try it again.
>
> Interestingly enough, on an amd machine, it worked as I expected with
> a bit more current version of -head but same version of acpica:
> debug.acpi.acpi_ca_version: 20130823
>
> cpus came up with cx_lowest set to C8 with Cmax in rc.conf
>
> cheers,
> Hiren
>

Setting Cx values is a bit confusing.  Things may not mean what you think.
CMax is always C8 because this is the largest possible value of a Cx state,
not because C8 is actually available.The reason for this is that some
systems have non-sequencial Cx states. That is the maximum value my be C5,
but C2 may not be available. So the idea is to allow ANY C-state up to the
maximum. LOWEST works well as long as no states are skipped. If they are,
you are limited to the states before the skipped state.

To see the actual available states, look at dev.cpu.0.cx_supported.

The recommended value for best power savings is :Cmax. That will allow
skipping over missing C-states. Also, the available states often differ
between AC power and battery. On my T320:
AC         dev.cpu.0.cx_supported: C1/1/1 C2/3/104
Battery  dev.cpu.0.cx_supported: C1/1/1 C2/2/80 C3/3/109

I am unsure why you are only seeing C1.
-- 
R. Kevin Oberman, Network Engineer, Retired
E-mail: rkoberman at gmail.com