[Beowulf] Re: Re: Home beowulf - NIC latencies
lindahl at pathscale.com
Mon Feb 14 13:58:43 EST 2005
On Mon, Feb 14, 2005 at 05:42:42PM +0000, Ashley Pittman wrote:
> If you had a bunch of sends to do to N remote processes then I'd expect
> you to post them in order (non-blocking) and wait for them all at the
> end, the time taken to do this should be (base_latency + ( (N-1) * M ))
> where M is the recpipiocal of the "issue rate". You can clearly see
> here that even for small number of batched sends (even a 2d/3d nearest
> neighbour matrix) the issue rate (that is how little CPU the send call
> consumes) is at least as important that the raw latency.
Unless I completely misunderstand your formula, M is not only the CPU
the send call consumes. It's easy to find situations (fast cpu, slow
network) where the cpu consumed isn't a part of M at all. Even for a
modern 1 GByte/sec network, cpu consumed might not be a part of M.
Reducing CPU consumed can't hurt. But reasoning about it seems to be
less useful than testing actual applications.
Beowulf mailing list, Beowulf at beowulf.org
To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
More information about the Beowulf