On Fri, Apr 17, 2009 at 01:29:09PM -0400, erik quanstrom wrote:
> > In some sense, logically (but not efficiently: read the caveats in the
> > Plan9 papers; a processor is nothing without tightly coupled memory, so
> > memory is not a remote pool sharable---Mach!),
>
> if you look closely enough, this kind of breaks down. numa
> machines are pretty popular these days (opteron, intel qpi-based
> processors). it's possible with a modest loss of performance to
> share memory across processors and not worry about it.
NUMA are, from my point of view, "tightly" connected.
By loosely, I mean a memory accessed by non dedicated processor
hardware means (if this makes sense). Moving data from different
memories via some IP based protocol or worse. But all in all,
finally a copy is put in the tightly connected memory, whether huge
caches, or dedicated main memory.
The disaster of Mach (I don't know if my bad english is responsible for
this, but in the Plan9 paper the "research" or "university" OS that is
implicitely gibed at is Mach) is a kind of example.
NUMA are sufficiently special beasts that the majority of huge computing
facilities have been done by clusters (because it was easier for
software only organizations).
This definitively doesn't mean NUMA has no raison d'être. On the
contrary, this is an argument supplementary to the distinction
between the UI (terminals) and the CPU.
--
Thierry Laronde (Alceste) <tlaronde +AT+ polynum +dot+ com>
http://www.kergis.com/
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