And Mark Hahn writes: > indeed, very nice. though also quite surprising - is it known that > FDR is so terrible for latency? seems astonishing to me.
FDR increases bandwidth by increasing the on-wire packet size and not any physical BW increase. Therefore, if you're sending packets that are too small, latency will suffer simply because you're still waiting on the same physical interface to digest a larger chunk. (Ok, that's more the 'o' term in LogP, but good enough.) I'm guessing that those of us in the small-packet regime assumed this from the get-go, so never really bothered checking. The nifty thing is that the posted results don't show *too* much loss for BW-tuned dual-rail QDR. (Um, ok, LogP shows that, too, but I'm lazy.) _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
