On Wednesday 28 March 2007, Mark Hahn wrote: > >> start timer > >> send(other,small-message) recv(first,small-message) > >> recv(other,small-message) send(first,small-message) > >> stop timer > >> > >> I'll actually see 2.4 us between the timer calls? if I understand, > >> aggregation would only help on a streaming test. in fact, this kind > >> of isolated RPC-like exchange is what I see most commonly. > > > > Assuming you could time it with any accuracy, yes. > > that's not an issue - rdtsc is perfectly good into the tens of ns range.
I'll have to hack together a rdtsc based mpi microbenchmark some day it seems =) > > I've seen ib_write_lat figures of ~1. > > well, I was assuming mpi - does anyone really write apps using ib > primitives? Sorry for being unclear here. What I wanted to say was that, unrelated to 1.5 us ping-pong on mpi I have also observed verbs level latency (ib_write_lat) of around 1 us. And that figure is not affected by any mvapich trickery :-). /Peter > in anycase, if this is a non-streaming latency result, it's pretty good; > enough to make quadrics look comprehensively out of the picture (guess > they've switched horses to 10GE anyway.)
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