Re: dbcool, envsys, powerd shutting down my machine

[Eduardo Horvath <eeh%NetBSD.org@localhost>]

I really don't know why I'm keeping this discussion going.  I doubt anyone 
else cares, but:

On Wed, 3 Feb 2016, Constantine A. Murenin wrote:

> On 2016-02-03 10:06, Eduardo Horvath wrote:
> > On Tue, 2 Feb 2016, Constantine A. Murenin wrote:
> > 
> > > Wouldn't the correct solution then be to kill the process-intensive jobs,
> > > instead of shutting down the whole system?
> > 
> > That doesn't really make too much sense.
> > 
> > In theory, if the CPU has a low power mode and the machine detects
> > thermal issues, you could lower the temperature by periodically switching
> > into the low power mode.  Some CPUs operate this way.
> > 
> > However, at the moment there's no way that a low power mode will generate
> > less heat than a no power mode.
> 
> I think the issue at stake are the false positives, during which powerd will
> rudely shutdown any box (w/ etc/powerd/scripts/sensor_temperature).
> 
> Also, I disagree that no power will always result in lower temperature,
> especially in the non-laptop environment:
> 
> 0. If your CPU is overheating, and you shutdown the whole box, it's quite
> likely that the other components within the enclosure will end up receiving
> extra heat due to the enclosure fans now being powered down.

Although you can always come up with a scenario based on some lousy 
design where shutting off the power is a bad idea, those cases are 
anomolous.  

If the box is overheating, either one of the fans has failed, the intake 
or exhaust ports are blocked, or the outside temperature is high enough 
that the fans are blowing heat into the box.  So no, pumping more energy 
into the box is counterproductive.

> 1. Also, if we talk about a Data Centre environment, wouldn't "graceful"
> shutdown from within the operating system simply initiate a restart sequence,
> potentially in an endless loop?

A shutdown should result in a shutdown.  A reboot should result in a 
reboot.  If a machine detects overtemp it shouldn't do either of those, it 
should power itself off.  Back in the olden days, computers couldn't turn 
off the power, so the best you could do is shut off the OS, put the CPU 
into a tight NOOP loop, and hope someone noticed and turned off the power 
before something fried.  Nowadays most machines can turn them selves off.

In a data center environment, there is usually a separate microcontroller
controlling the machine and doing environmental monitoring.  When it 
detects high temperatures it may try to tell the OS to cool it, but for a 
true overtemp situation it will turn off the power rails.  

> 
> I think system shutdown should be on an opt-in, not an opt-out, basis.
> 
> C.
> 
>