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Date: Sun, 4 Nov 2001 07:32:31 -0800 (PST)
From: John Alvord <jalvo@mbay.net>
To: Erik Mouw <J.A.K.Mouw@its.tudelft.nl>
cc: Roy Sigurd Karlsbakk <roy@karlsbakk.net>,
        Alan Cox <alan@lxorguk.ukuu.org.uk>,
        Thomas Lussnig <tlussnig@bewegungsmelder.de>,
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        khttpd mailing list <khttpd-users@zgp.org>,
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Subject: Re: [khttpd-users] khttpd vs tux
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On Sun, 4 Nov 2001, Erik Mouw wrote:

> On Sat, Nov 03, 2001 at 08:18:19PM +0100, Roy Sigurd Karlsbakk wrote:
> > > Each GigE card will need its own 66MHz PCI bus. Each PCI bridge will need
> > > to be coming off a memory bus that can sustain all of these and the CPU
> > > at once.
> > >
> > > At that point it really doesnt look much like a PC.
> > 
> > How much raw speed do you think I can manage to get out of a really cool
> > n-way server from Compaq? I beleive we'll go for a Compaq server, as
> > that's what's been decided some time ago.
> 
> Not that much. Alan's point is that you're pushing the limit of the
> memory bandwidth, not the number of CPUs. This is the single reason
> that high traffic websites either use some serious non-PC hardware (IBM
> Z-series, for example) or a large number of PCs in parallel to share
> the load.
> 
> > I read something by Linus about linux scalability, and I beleive he said
> > that 'linux [2.4] scales good up to 4 cpus, but not that good futher on
> > [to 8?]'. Can anyone fill in the holes here?
> 
> The number of CPUs really doesn't matter in this case. With several
> GigE cards memory bandwidth and latency is your main problem.

Interesting parallel...

In the last few years there have been multiple cases where people reported
benchmarks where a dual processir gave less thruput then a single
processor. In most cases, the single processor benchmark had saturated the
memory bandwidth and a second processor didn't make much difference.

This was on "cheap" multi-processors.

john alvord

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