Could you at least provide a one-line explanation of that statement?
On Dec 13, 2010, at 7:31 AM, Jeff Squyres wrote: > Also note that recent versions of the Linux kernel have changed what > sched_yield() does -- it no longer does essentially what Ralph describes > below. Google around to find those discussions. > > > On Dec 9, 2010, at 4:07 PM, Ralph Castain wrote: > >> Sorry for delay - am occupied with my day job. >> >> Yes, that is correct to an extent. When you yield the processor, all that >> happens is that you surrender the rest of your scheduled time slice back to >> the OS. The OS then cycles thru its scheduler and sequentially assigns the >> processor to the line of waiting processes. Eventually, the OS will cycle >> back to your process, and you'll begin cranking again. >> >> So if no other process wants or needs attention, then yes - it will cycle >> back around to you pretty quickly. In cases where only system processes are >> running (besides my MPI ones, of course), then I'll typically see cpu usage >> drop a few percentage points - down to like 95% - because most system tools >> are very courteous and call yield is they don't need to do something. If >> there is something out there that wants time, or is less courteous, then my >> cpu usage can change a great deal. >> >> Note, though, that top and ps are -very- coarse measuring tools. You'll >> probably see them reading more like 100% simply because, averaged out over >> their sampling periods, nobody else is using enough to measure the >> difference. >> >> >> On Dec 9, 2010, at 1:37 PM, Hicham Mouline wrote: >> >>>> -----Original Message----- >>>> From: users-boun...@open-mpi.org [mailto:users-boun...@open-mpi.org] On >>>> Behalf Of Eugene Loh >>>> Sent: 08 December 2010 16:19 >>>> To: Open MPI Users >>>> Subject: Re: [OMPI users] curious behavior during wait for broadcast: >>>> 100% cpu >>>> >>>> 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. >>>> >>> Any clarifications? >>> >>> _______________________________________________ >>> users mailing list >>> us...@open-mpi.org >>> http://www.open-mpi.org/mailman/listinfo.cgi/users >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org >> http://www.open-mpi.org/mailman/listinfo.cgi/users > > > -- > Jeff Squyres > jsquy...@cisco.com > For corporate legal information go to: > http://www.cisco.com/web/about/doing_business/legal/cri/ > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
