[Beowulf] slightly [OT] smp boxes

Mark Hahn hahn at mcmaster.ca
Sun Oct 19 17:15:03 EDT 2008


> The SiCortex systems are clusters of 6-core SMPs.  There is no load/store 
> access to memory on other nodes, although the interconnect is fast enough to 
> make software access to remote memory quite interesting.

interesting way to put it, since competing interconnects are at least 
as fast (I'm thinking about the usual IB claim of ~1 us latency).

> I've been coding shmem and GASnet implementations for the SiCortex 
> interconnect recently, and on the older 500 MHz systems a "put" takes about 
> 800 ns and a "get" takes a little under  3 microseconds before any particular 
so the 800ns put is half RTT for two nodes doing ping-pong puts?

> On the remote-paging side, I put together a prototype that gets about 2 
> GB/sec and 64K page fault latencies under 100 microseconds, again, not 
> optimized.

ouch.  do you know how much of that time is due to slow MMU interaction?
(at 2 GB/s, the wiretime for 64k should be 33 us, if I calculate correctly)


> after all.  I am kind of amused by all the press and angst about "multicore", 
well, academics need _something_ to motivate grants, and the gov isn't 
likley to support all the nation's CS depts on gaming research ;)
also, I suspect intel and perhaps sun have encouraged the brouhaha.
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