Date: Sun, 30 Apr 2000 16:38:24 +0200 From: Dave Boers <djb@ifa.au.dk> To: Karl Pielorz <kpielorz@tdx.co.uk> Cc: Steve Passe <smp@csn.net>, smp@FreeBSD.ORG Subject: Re: hlt instructions and temperature issues Message-ID: <20000430163824.A1093@relativity.student.utwente.nl> In-Reply-To: <390C4185.5C07088A@tdx.co.uk>; from kpielorz@tdx.co.uk on Sun, Apr 30, 2000 at 03:21:57PM %2B0100 References: <200004300350.VAA13194@Ilsa.StevesCafe.com> <20000430122943.A52481@relativity.student.utwente.nl> <20000430152339.A453@relativity.student.utwente.nl> <390C4185.5C07088A@tdx.co.uk>
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On Sun, Apr 30, 2000 at 03:21:57PM +0100, Karl Pielorz wrote:
> > I personally wouldn't worry about 5% performance difference, and go for the
> > lower temperature and increased stability. But others may have different
> > opinions. My proposal is therefore to make the hlt instruction a kernel
> > option for SMP systems. That way everyone can experiment for themselves and
> > possible problems may be detected.
>
> Everyone,
>
> This thread has been a fascinating walk through CPU temperatures under SMP -
> but surely, no one should be designing a system that relies on the 'thermal
> characteristics of the software running' to ensure safe operation? - If the
> spec says you need to dissipate 32 Watts of heat from the CPU, you design a
> system to dissipate 32 Watts (probably a bit more for 'safety'? :)...
Agreed. However, I can think of a number of reasons why it would be
sometimes preferable to have the system cooler on average even though it
should be designed to handle all the heat even at full load, and surely you
can as well. So I think it is nice to have the hlt's as an option.
> Taking it to an extreme, it would be like building a system that falls over
> when it 'happens to be busy' one day, 'cause someone ran something
> computationally intensive? - I know for a fact these systems do exist, but we
> don't really want to be helping sweep the cause under the rug do we?
No. I don't.
> I don't like the 5% speed decrease either - our SMP systems are SMP because we
> need the speed. They are built to handle the thermals - so the thought of
> dropping 5% in speed isn't appealing...
A matter of choice. And there isn't just a speed decrease, there can be an
increase also, as it was shown by Steve. It merely means that different
tasks will run at different speeds, some lower, some higher.
> At the very worst can this be made a 'default off' option? :-)
I'd go for that, yes.
> And, I wasn't be funny - the thread _really_ was interesting... :)
I still is. :-)
Dave.
--
djb@ifa.au.dk d.j.boers@tn.utwente.nl
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