[OmniOS-discuss] [discuss] illumos power management

[randyf at sibernet.com]

On Wed, 13 Nov 2013, Paul B. Henson wrote:

> On 11/13/2013 11:24 AM, Garrett D'Amore wrote:
>> CPU power management is unlikely to do much for you.  Its better to rely
>> on C-states to save power on modern systems.
>
> I'm not sure how to interpret that; the power.conf man page says that if 
> cpu_deep_idle is enabled "On X86 systems this can translate to the use of 
> ACPI C-States beyond C1", so it seems illumos is already using C states for 
> CPU power management?

Indeed.

>
>> Frankly, very very few components on typical illumos based
>> systems even support power management apart from the disk subsystem.
>
> Probably only disks and CPU I would think, although it would be nice to be 
> able to list out what the system thinks it could manage. I definitely don't 
> want to spin down the disks, but I wouldn't mind saving a few watts here and 
> there on the CPU. So maybe something like:
>
> autopm                  disable
> autoS3                  disable
> cpupm                   enable
> cpu_deep_idle           enable

CPUPM can be independent of autopm, so if you desire CPUPM and not disk 
PM, setting autopm to 'disable' is correct (note, autoS3 is only relevant 
if S3-support is 'enable').  Also, "cpupm" can take 2 arguments, the 
second being one of 'event-mode' or 'poll-mode' (the default being 
'event-mode', which is the mode that is separated from autopm).  So you 
might wish to change 'cpupm enable' to 'cpupm enable event-mode' just so 
it is explicit (you might also wish to add 'S3-support disable' just to 
make sure the system won't ever try to suspend).

Also, you *can* specify different PM capabilities for different disks. 
Multi-terabyte drives are cheap, and could serve as the backup media. 
There could well be value of having backup disks spindown, but keep the OS 
disks always-on (you would have to enable autopm for this action, though).

Lastly, powertop(1m) can be used to see how well CPUPM is working for you.

>
>> The display subsystem typically uses its own power management which
>> doesn't participate with the rest of illumos' power management
>> framework, IIRC.)

I am not aware of any x86 display drivers that have a power(9e) entry 
point, but if it does, it will partake in the PM framework operations.

>
> Unlike good old SPARC boxes, my x86 "headless" server has a graphics adapter 
> in it. As I'm using a serial console, all it ever displays after boot is a 
> blank screen, can't imagine it takes much power...

   It may be more than you might think.  The backlight on flat panels is 
the biggest draw, and may not be trivial.  A monitor rendering black will 
still have the gun scanning and the tube lit.  You might prefer either 
removing the display adapter, unplugging the monitor, or starting X so 
that it can run display PM.


   Cheers!

 	---- Randy