Date: Fri, 05 Nov 1999 10:22:08 -0800 From: Darryl Okahata <darrylo@sr.hp.com> To: "Eric J. Schwertfeger" <ejs@bfd.com> Cc: Adam Strohl <adams@digitalspark.net>, "Daniel O'Connor" <doconnor@gsoft.com.au>, freebsd-smp@FreeBSD.ORG Subject: Re: Dual Celeron + FreeBSD? Message-ID: <199911051822.KAA25575@mina.sr.hp.com> In-Reply-To: Your message of "Fri, 05 Nov 1999 08:45:04 PST." <Pine.BSF.4.10.9911050836470.14598-100000@harlie.bfd.com>
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"Eric J. Schwertfeger" <ejs@bfd.com> wrote:
> I agree for the most part, on single-processor machines, though it's
> actually a quarter the cache. The reduced, faster cache causes a single
> celeron to be more memory-bandwidth sensitive. An SMP machine, however,
> has two CPUs contending for the same bandwidth, and for some processes,
> that can be fatal.
I'd like to emphasize Eric's point. With SMP, memory bandwidth and
contention are very important:
* A non-overclocked Celeron has a FSB of 66MHz. P2s (350MHz+) and above
have a 100MHz FSB.
* Celerons have only 128K L2 cache, although it is zero-wait state.
With SMP, you can have processes that cause lots of memory
contention (e.g., simple calls like "bzero()", "memcpy()", etc, can
blow away the cache contents, and force the CPU to go directly to main
memory). A larger cache helps to prevent memory contention between
CPUs (although the non-zero-wait-state nature makes it less useful).
> I've done make buildworld's on both my dual Celeron and my dual PPro (the
> ones with 512K cache). The difference between single and dual celeron is
> minimal, about 10%. On the dual PPro machine, the speed improvement,
> using the same disk subsystem, was 80%. Yes, on processes that aren't
> memory intensive, dual Celerons rock. In fact, on most things, I see
> closer to 40-50% improvement with dual Celerons, the make buildworld is
> rather memory intensive.
The numbers I've seen thrown around (and I haven't verified them)
are:
2 Celerons -> ~1.5X a single CPU
2 P2s (350MHz+) -> ~1.8X a single CPU
This is, of course, simplistic.
--
Darryl Okahata
darrylo@sr.hp.com
DISCLAIMER: this message is the author's personal opinion and does not
constitute the support, opinion, or policy of Agilent Technologies, or
of the little green men that have been following him all day.
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