Re: [patch] CFS scheduler, -v8

Willy Tarreau
2007-05-11T19:39:33Z

On Fri, May 11, 2007 at 07:18:25PM +0000, Pavel Machek wrote:
> Hi!
>
> > > Also notice that current cpus were not designed to work 300 years.
> > > When we have hw designed for 50 years+, we can start to worry.
> >
> > Indeed. CPU manufacturers don't seem to talk about it very much, and
> > searching for it with google on intel.com comes up with
> >
> > The failure rate and Mean Time Between Failure (MTBF) data is not
> > currently available on our website. You may contact Intel?
> > Customer Support for this information.
> >
> > which seems to be just a fancy way of saying "we don't actually want to
> > talk about it". Probably not because it's actually all that bad, but
> > simply because people don't think about it, and there's no reason a CPU
> > manufacturer would *want* people to think about it.
> >
> > But if you wondered why server CPU's usually run at a lower frequency,
> > it's because of MTBF issues. I think a desktop CPU is usually specced to
> > run for 5 years (and that's expecting that it's turned off or at least
> > idle much of the time), while a server CPU is expected to last longer and
> > be active a much bigger percentage of time.
> >
> > ("Active" == "heat" == "more damage due to atom migration etc". Which is
> > part of why you're not supposed to overclock stuff: it may well work well
> > for you, but for all you know it will cut your expected CPU life by 90%).
>
> Actually, when I talked with AMD, they told me that cpus should last
> 10 years *at their max specced temperature*... which is 95Celsius. So
> overclocking is not that evil, according to my info.

I tend to believe that. I've slowed down the FANs on my dual-athlon XP
to silent them, and I found the system to be (apparently) stable till
96 deg Celsius with FANs unplugged. So I regulated them in order to maintain
a temperature below 90 deg for a safety margin, and they seem to be as
happy as my ears. They've been like that for the last 3-4 years, I don't
remember.

On a related note, older technology is less sensible. My old VAX VLC4000
from 1991 which received a small heatsink in exchange for its noisy fans
is still doing well in an closed place. I'm more worried for the EPROMs
which store the boot code. Also, I think that the RS6000 processed at
half-micron which run the Mars rovers might run for hundreds of years
at 30 MHz.

> (That would mean way more than 10 years if you use your cpu
> 'normally'.)
>
> But I guess capacitors from cpu power supply will hate you running cpu
> at 95C...

even at 60, many of them die within a few years. Bu I think we're
"slightly" off-topic now...

> Pavel

Cheers
Willy