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Subject: Re: [OMPI users] curious behavior during wait for broadcast: 100% cpu
From: Hicham Mouline (hicham_at_[hidden])
Date: 2010-12-13 10:56:10


very clear, thanks very much.
 
 
-----Original Message-----
From: "Ralph Castain" [rhc_at_[hidden]]
Date: 13/12/2010 03:49 PM
To: "Open MPI Users"
Subject: Re: [OMPI users] curious behavior during wait for broadcast: 100% cpu

Thanks for the link!

Just to clarify for the list, my original statement is essentially correct. When calling sched_yield, we give up the remaining portion of our time slice.

The issue in the kernel world centers around where to put you in the scheduling cycle once you have called sched_yield. Do you go to the end of the schedule for your priority? Do you go to the end of the schedule for all priorities? Or...where?

Looks like they decided to not decide, and left several options available. Not entirely clear of the default, and they recommend we not use sched_yield and release the time some other method. We'll take this up on the developer list to see what (if anything) we want to do about it.

Bottom line for users: the results remain the same. If no other process wants time, you'll continue to see near 100% utilization even if we yield because we will always poll for some time before deciding to yield.