[OmniOS-discuss] [discuss] illumos power management

[Garrett D'Amore]

CPU power management is unlikely to do much for you.  Its better to rely on
C-states to save power on modern systems.  That said, there are some known
bugs with deep C states and some drivers; we don't ordinarily recommend
setting it for servers.

The autopm should probably just be set to disable for your configuration.
 Letting the system power down your hard drives is likely to be the root of
your problems.  You don't need or want to power the drives down, and
probably you don't want to power management anything else.  (Frankly, very
very few components on typical illumos based systems even support power
management apart from the disk subsystem.  The display subsystem typically
uses its own power management which doesn't participate with the rest of
illumos' power management framework, IIRC.)

Indeed, the illumos power management framework is kind of a shambles right
now -- consisting of at least two separate generations of code, a high
level of complexity, and almost no substantial support from the various
things that *should* support it.

At one point I was discussing with Randy Fishel about some ideas I had for
simplifying things substantially. Most generally, these days involvement
with a core power management is probably *not* what you want, except to
indicate "policy"  -- modern devices (disk drives notwithstanding) can
generally raise and lower power so quickly that its best to just let the
drivers do their own power management explicitly, with only a few
monitoring and policy hooks.  This would lead to a vastly simpler power
framework, which would probably be more likely to be taken up driver
authors than the current mess.



On Tue, Nov 12, 2013 at 2:52 PM, Paul B. Henson <henson at acm.org> wrote:

> I think the storage server I'm working on at home (current omnios stable)
> is
> spinning down disks; whenever I get back to it after not touching it for a
> while, anything touching my export pool (dual 6 x 3TB WD Red RAIDZ2) takes
> a
> long time to respond, and then goes back to normal.
>
> My current power.conf is:
>
> -----
> autopm                  enable
> autoS3                  disable
>
> cpupm                   enable
> cpu_deep_idle           enable
> cpu-threshold           1s
> -----
>
> I had thought that when running on server class hardware the default was
> not
> to spin down drives, but perhaps I was mistaken? Hmm, or maybe the default
> is to just skip power management completely, and explicitly turning it on
> turned on everything.
>
> I'm thinking about adding "system-threshold always-on" to the
> configuration,
> which I guess will disable all power down functionality, other than CPU,
> which is controlled by the "cpu-threshold" parameter? What other power
> savings would this turnoff? I am in general in favor of saving energy :),
> other than for the disks, as the latency is too high and causes too much of
> a delay, and it's not clear if setting the system-threshold to stop
> spinning
> down disks will also disable other potentially desirable power savings. I
> guess the other option would be to explicitly configure device-thresholds
> for all of the disks individually. Is there any way to list what components
> of a system support power management?
>
> While on the subject, any thoughts on event-mode vs poll-mode for cpupm?
> It's not clear from the man page what the default is if you just set it to
> "enable".
>
> Thanks.
>
>
>
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