Hi Zack! On Sat, Oct 02, 2010 at 08:39:06AM -0700, Zack Weinberg wrote: > On Sat, Oct 2, 2010 at 6:01 AM, Manuel Prinz <man...@debian.org> wrote: > >> On 29 September 2010 at 18:22, Zack Weinberg wrote: > >> | (on an 8-core machine), CPU utilization jumps *immediately* from 98% idle > >> | to 20% user, 70% system, 12% idle. strace reveals that each slave is > >> | spinning through poll() calls with timeout zero, rather than blocking > >> | until a message arrives, as the documentation for mpi.probe() suggests > >> | should happen. > ... > > Well, no. Actually, this behavior is by design. I'm not sure about the > > details > > exactly but can get back to Jeff if you're interested in those. This is > > coming > > up every now and then in the BTS or the user list. Open MPI is basically > > burning > > every free cycle that is not used for computation (busy wait). There are no > > immediate plans of changing that, as far as I know.
I did some reading and it seems the Open MPI indeed does support two modes of waiting: aggressive and degraded. The default behavior is "aggressive", but you can switch them by setting the mpi_yield_when_idle MCA parameter. See the following FAQ entries (and links therein): http://www.open-mpi.org/faq/?category=running#force-aggressive-degraded http://www.open-mpi.org/faq/?category=running#oversubscribing I guess this is basically the behaviour you want. It would be great if you could give it a try and report back if it works for you. If it doesn't do what you (and I) expect, I'll forward this issue upstream. Best regards, Manuel -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
