On Mar 5, 2009, at 8:50 AM, Joe Landman wrote:
Jeff Squyres wrote:
On Mar 5, 2009, at 10:33 AM, Gerry Creager wrote:
We've been playing with it in a coupled atmosphere-ocean model to
allow
the two to synchronize and exchange data. The models have differing
levels of physics complexity and the time step requirements are
significantly different. To sync them up we have to know where the
timesteps are identical, stop the process, exchange data and
continue.
We've been playing with barrier to help.
I'm not sure I understand -- "help" meaning what?
If you're exchanging data at the end of an iteration, then you
effectively have a synchronization anyway -- no need for an extra
barrier synchronization.
Hi Jeff and Gerry:
I think what Gerry means is that they have 2 distinct models
running as different processes, and every now and then, the time
steps of the models agree ... so both models register the same time
to within some uncertainty or pre-defined accuracy. At that point,
they exchange information. So it is not necessarily a
synchronization at every time step, its likely at every Nth time
step for one code, and every Mth for the other code. Of course this
assumes fixed size time steps which might not be the case.
Regardless, at the point where the times are determined to be
equal, the models need to exchange data. Which means if one got
there sooner than the other, that one has to wait for the other.
Continuing calculating without the data exchange would be, I am
guessing, a waste of processor cycles as the models are coupled, and
continuing without the coupling would be incorrect.
Ummm....not to put gasoline on the fire, but...if the data exchange is
blocking, why do you need to call a barrier op first? Just use an
appropriate blocking data exchange call (collective or whatever) and
it will "barrier" anyway.
Joe
--
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics LLC,
email: land...@scalableinformatics.com
web : http://www.scalableinformatics.com
http://jackrabbit.scalableinformatics.com
phone: +1 734 786 8423 x121
fax : +1 866 888 3112
cell : +1 734 612 4615
_______________________________________________
users mailing list
us...@open-mpi.org
http://www.open-mpi.org/mailman/listinfo.cgi/users
