On Jul 30, 2014, at 20:37 , Ralph Castain <r...@open-mpi.org> wrote:
> > On Jul 30, 2014, at 5:25 PM, George Bosilca <bosi...@icl.utk.edu> wrote: > >> >> On Jul 30, 2014, at 18:00 , Jeff Squyres (jsquyres) <jsquy...@cisco.com> >> wrote: >> >>> WHAT: Should we make the job size (i.e., initial number of procs) available >>> in OPAL? >>> >>> WHY: At least 2 BTLs are using this info (*more below) >>> >>> WHERE: usnic and ugni >>> >>> TIMEOUT: there's already been some inflammatory emails about this; let's >>> discuss next Tuesday on the teleconf: Tue, 5 Aug 2014 >>> >>> MORE DETAIL: >>> >>> This is an open question. We *have* the information at the time that the >>> BTLs are initialized: do we allow that information to go down to OPAL? >>> >>> Ralph added this info down in OPAL in r32355, but George reverted it in >>> r32361. >>> >>> Points for: YES, WE SHOULD >>> +++ 2 BTLs were using it (usinc, ugni) >>> +++ Other RTE job-related info are already in OPAL (num local ranks, local >>> rank) >>> >>> Points for: NO, WE SHOULD NOT >>> --- What exactly is this number (e.g., num currently-connected procs?), and >>> when is it updated? >>> --- We need to precisely delineate what belongs in OPAL vs. above-OPAL >> --- Using this information to configure the communication environment limits >> the scope of communication substrate to a static application (in number of >> participants). Under this assumption, one can simply wait until the first >> add_proc to compute the number of processes, solution as “correct” as the >> current one. > > Not necessarily - it depends on how it is used, and how it is communicated. > Some of us have explored other options for using this that aren’t static, but > where the info is of use. This is a little bit too much hand waving to be constructive. Some other folks in the field have developed many communications libraries, and none of them needed a random number of potential processes to initialize themselves correctly. >> The other “global” information that were made available in OPAL >> (num_local_peers and my_local_rank) are only used by local BTL (SM, SMCUDA >> and VADER). Moreover, my_local_rank is only used to decide who initialize >> the backend file, thing that can easily be done using an atomic operation. >> The number of local processes is used to prevent SM from activating itself >> if we don’t have at least 2 processes per node. So, their usage is minimally >> invasive, and can eventually be phased out with a little effort. > > FWIW: the new PMI abstraction is in OPAL because it is RTE-agnostic. So all > the info being discussed will actually be captured originally in the OPAL > layer, and stored in the OPAL dstore framework. In the current code, the RTE > grabs the data and exposes it to the OMPI layer, which then pushes it back > down to the OPAL proc.h struct. > > <shrug> since anyone can freely query the info from opal/pmix or opal/dstore, > it is really irrelevant in some ways. The info is there, in the OPAL layer, > prior to BTL's being initialized. If you don't want it in a global storage, > people can just get it from the appropriate OPAL API. > > So what are we actually debating here? Global storage vs API call? Our goals in this project are clearly orthogonal. I put a lot of effort into this move because I need to use the BTLs without PMI, without RTE. In fact the question boils down to: Do you want to be able to use the BTL to bootstrap the RTE or not? If yes, then the number of processes is out of the picture, either as an API or as a global storage. George. > >> >> George. >> >> >>> FWIW: here's how ompi_process_info.num_procs was used before the BTL move >>> down to OPAL: >>> >>> - usnic: for a minor latency optimization / sizing of a shared receive >>> buffer queue length, and for the initial size of a peer lookup hash >>> - ugni: to determine the size of the per-peer buffers used for send/recv >>> communication >>> >>> -- >>> Jeff Squyres >>> jsquy...@cisco.com >>> For corporate legal information go to: >>> http://www.cisco.com/web/about/doing_business/legal/cri/ >>> >>> _______________________________________________ >>> devel mailing list >>> de...@open-mpi.org >>> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/devel >>> Link to this post: >>> http://www.open-mpi.org/community/lists/devel/2014/07/15373.php >> >> _______________________________________________ >> devel mailing list >> de...@open-mpi.org >> Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/devel >> Link to this post: >> http://www.open-mpi.org/community/lists/devel/2014/07/15378.php > > _______________________________________________ > devel mailing list > de...@open-mpi.org > Subscription: http://www.open-mpi.org/mailman/listinfo.cgi/devel > Link to this post: > http://www.open-mpi.org/community/lists/devel/2014/07/15379.php
