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Subject: Re: [OMPI users] curious behavior during wait for broadcast: 100% cpu
From: Eugene Loh (eugene.loh_at_[hidden])
Date: 2010-12-08 11:18:57


Ralph Castain wrote:

>I know we have said this many times - OMPI made a design decision to poll hard while waiting for messages to arrive to minimize latency.
>
>If you want to decrease cpu usage, you can use the yield_when_idle option (it will cost you some latency, though) - see ompi_info --param ompi all
>
>
I wouldn't mind some clarification here. Would CPU usage really
decrease, or would other processes simply have an easier time getting
cycles? My impression of yield was that if there were no one to yield
to, the "yielding" process would still go hard. Conversely, turning on
"yield" would still show 100% cpu, but it would be easier for other
processes to get time.

>Or don't set affinity and we won't be as aggressive - but you'll lose some performance
>
>Choice is yours! :-)
>
>