On Thu, 2010-09-09 at 01:24 -0600, Ralph Castain wrote: > As people have said, these time values are to be expected. All they > reflect is the time difference spent in reduce waiting for the slowest > process to catch up to everyone else. The barrier removes that factor > by forcing all processes to start from the same place. > > > No mystery here - just a reflection of the fact that your processes > arrive at the MPI_Reduce calls at different times.
Yes, however, it seems Gabriele is saying the total execution time *drops* by ~500 s when the barrier is put *in*. (Is that the right way around, Gabriele?) That's harder to explain as a sync issue. > On Sep 9, 2010, at 1:14 AM, Gabriele Fatigati wrote: > > > More in depth, > > > > > > total execution time without Barrier is about 10000 sec. > > > > > > Total execution time with Barrier+Reduce is 9453, with 128 procs. > > > > 2010/9/9 Terry Frankcombe <te...@chem.gu.se> > > Gabriele, > > > > Can you clarify... those timings are what is reported for > > the reduction > > call specifically, not the total execution time? > > > > If so, then the difference is, to a first approximation, the > > time you > > spend sitting idly by doing absolutely nothing waiting at > > the barrier. > > > > Ciao > > Terry > > > > > > -- > > Dr. Terry Frankcombe > > Research School of Chemistry, Australian National University > > Ph: (+61) 0417 163 509 Skype: terry.frankcombe > > > > > > _______________________________________________ > > users mailing list > > us...@open-mpi.org > > http://www.open-mpi.org/mailman/listinfo.cgi/users > > > > > > > > > > > > -- > > Ing. Gabriele Fatigati > > > > Parallel programmer > > > > CINECA Systems & Tecnologies Department > > > > Supercomputing Group > > > > Via Magnanelli 6/3, Casalecchio di Reno (BO) Italy > > > > www.cineca.it Tel: +39 051 6171722 > > > > g.fatigati [AT] cineca.it > > > > _______________________________________________ > > 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
