the Bcast in coll/sm coll modules have priority (see ompi_info --all)
for a given function (e,g. bcast) the module which implements it and has the highest priority is used. note a module can disqualify itself on a given communicator (e.g. coll/sm on I ter node communucator). by default, coll/tuned is very likely used. this module is a bit special since it selects a given algorithm based on communicator and message size. if you give a high priority to coll/sm, then it will be used for single node intra communicators, assuming coll/sm implements all collective primitives. Cheers, Gilles On Thursday, June 30, 2016, Saliya Ekanayake <esal...@gmail.com> wrote: > Thank you, Gilles. > > What is the bcast I should look for? In general, how do I know which > module was used to for which communication - can I print this info? > On Jun 30, 2016 3:19 AM, "Gilles Gouaillardet" <gil...@rist.or.jp > <javascript:_e(%7B%7D,'cvml','gil...@rist.or.jp');>> wrote: > >> 1) is correct. coll/sm is disqualified if the communicator is an inter >> communicator or the communicator spans on several nodes. >> >> you can have a look at the source code, and you will not that bcast does >> not use send/recv. instead, it uses a shared memory, so hopefully, it is >> faster than other modules >> >> >> Cheers, >> >> >> Gilles >> On 6/30/2016 3:04 PM, Saliya Ekanayake wrote: >> >> Hi, >> >> Looking at the *ompi/mca/coll/sm/coll_sm_module.c* it seems this module >> will be used only if the calling communicator solely groups processes >> within a node. I've got two questions here. >> >> 1. So is my understanding correct that for something like MPI_COMM_WORLD >> where world is multiple processes within a node across many nodes, this >> module will not be used? >> >> 2. If 1, is correct then are there any shared memory optimizations that >> happen when a collective like bcast or allreduce is called, so that >> communicating within a node is done efficiently through memory? >> >> Thank you, >> Saliya >> >> >> -- >> Saliya Ekanayake >> Ph.D. Candidate | Research Assistant >> School of Informatics and Computing | Digital Science Center >> Indiana University, Bloomington >> >> >> >> _______________________________________________ >> users mailing listus...@open-mpi.org >> <javascript:_e(%7B%7D,'cvml','us...@open-mpi.org');> >> Subscription: https://www.open-mpi.org/mailman/listinfo.cgi/users >> Link to this post: >> http://www.open-mpi.org/community/lists/users/2016/06/29564.php >> >> >> >> _______________________________________________ >> users mailing list >> us...@open-mpi.org <javascript:_e(%7B%7D,'cvml','us...@open-mpi.org');> >> Subscription: https://www.open-mpi.org/mailman/listinfo.cgi/users >> Link to this post: >> http://www.open-mpi.org/community/lists/users/2016/06/29565.php >> >
