linux-kernel - Re: [patch] CFS scheduler, -v8

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Message-ID: <20070511193751.GC20383@1wt.eu>
Date:	Fri, 11 May 2007 21:37:51 +0200
From:	Willy Tarreau <w@....eu>
To:	Pavel Machek <pavel@....cz>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Esben Nielsen <nielsen.esben@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Gene Heskett <gene.heskett@...il.com>, Mark Lord <lkml@....ca>,
	Zach Carter <linux@...hcarter.com>,
	buddabrod <buddabrod@...il.com>
Subject: Re: [patch] CFS scheduler, -v8

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

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