Re: FreeBSD is now self-hosting on the UltraSPARC T1

On 5/23/06, Lars Heidieker <lars_at_heidieker.de> wrote:
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> On 22 May 2006, at 22:26, Darren Pilgrim wrote:
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> > Wilko Bulte wrote:
> >> On Mon, May 22, 2006 at 09:43:11PM +0200, Claus Guttesen wrote..
> >>>>>>> on topic, the Opterons aren't SMP either, and neither are the
> >>>> ht-Xeons...
> >>>>>> ...
> >>>>> The MultiProcessor Opterons are _NOT_ SMP, they are _NUMA_
> >>>>> machines,
> >>> Not really related to the original topic any longer, is it?
> >> Decent bikesheds never are..
> >
> > At least people are being polite and not messing up the threading
> > by changing the subject header. :)
> >
> Yes that would be extremely NUMA because of the latencies occurring
> with such a thread migration  ;-)
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As a side note here, I'm working on the Opteron-isnt-SMP thing at the
moment.... I'm just calling it "OPTERON", since.... well.... nothing
else fits with it very well, and nothing else FreeBSD runs on supports
it anyway, I believe.

>From what I can tell, it would be.... unwise to classify Opteron as
NUMA, atleast to the kernel, since the overhead for real NUMA
clusters, with scheduling, and VM stuff would be somewhat excessive.
Opteron is logically NUMA, (When using multiple sockets), but
practically, I'm finding there's an excessive performance penalty when
you try to treat it strictly as such, as compared to calling it SMP,
so the implimentation is actually ending up somewhere in between.

Note that the above applies only to MULTIPLE SOCKETS. A dual core
Opteron, or Athlon64 X2 in a single socket is, in every sense of the
word, SMP.

I don't even want to get into naming nightmare of multiple dual core
Opterons. ;)

As for Intel's HT.... I suggest, "EXTRA_OVERHEAD_JUST_FOR_FUN", or
alternately, "LEAVE_THE_EBRAKE_ON". Perhaps in light of Colin's
thing.... "READ_MY_KEYS" would work, too.

--- Harrison Grundy