On 10/22/2010 12:53 AM, Arthur Machlas wrote:
On Thu, Oct 21, 2010 at 8:15 PM, Andrew Reid<reidac@bellatlantic.net> wrote:But I'm curious if anyone on the list knows the rationale for distributing kernels with this set to 32. Is that just a reasonable number that's never been updated? Or is there some complication that arises after 32 cores, and should I be more careful about tuning other parameters?I've always set the number of cores to exactly how many I have x2 when I roll my own, which on my puny systems is either 4 or 8. I seem to recall reading that there is a slight performance hit for every core you support.
Correct. The amount of effort needed for cross-CPU communication, cache coherency and OS process coordination increases much more than linearly as you add CPUs.
Crossbar communication (introduced first, I think, by DEC/Compaq in 2001) eliminated a lot of the latency in multi-CPU communications which plagues bus-based systems.
AMD used a similar mesh in it's dual-core CPUs (not surprising, since many DEC engineer went to AMD). Harder to design, but much faster.
Intel's first (and 2nd?) gen multi-core machines were bus-based; easier to design, quicker to get to market, but a lot slower.
(OP's machine is certainly NUMA, where communication between cores on a chip is much faster than communication with cores on a different chip.)
Or was it memory hit? Or was that a bong hit I'm thinking
of?
-- Seek truth from facts.