[Beowulf] Re: Re: Home beowulf - NIC latencies

Greg Lindahl lindahl at pathscale.com
Fri Feb 18 01:44:34 EST 2005


On Tue, Feb 15, 2005 at 07:34:50AM -0700, Keith D. Underwood wrote:
> 
> > c) ban of the ANY_SENDER wildcard: a world of optimization goes away 
> > with this convenience.
> 
> Um, our apps guys say this is more than a convenience.  Apparently,
> sometimes you don't exactly know who you are going to receive from. 
> Would you rather them post receives from 4000 nodes and cancel the ones
> that don't send to that node after a while?

That's a good reason to use it. The fundamental problem is that
supporting both ANY_TAG and ANY_SENDER efficiently is really
annoying. So most implementers would prefer to support ANY_TAG
efficiently and ANY_SENDER less efficiently.

And then those pesky users (life is much simpler when you only run
benchmarks that you write yourself, you know ;-) go use ANY_SENDER,
usually because they think it's faster when say 4 nodes are sending
you something at roughly the same time. Instead, we'd prefer that they
use Irecv for that.

-- greg



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