On Jul 18, 2013, at 8:17 AM, "David Goodell (dgoodell)" <dgood...@cisco.com> wrote:
> On Jul 18, 2013, at 9:53 AM, Ralph Castain <r...@open-mpi.org> wrote: > >> On Jul 18, 2013, at 7:05 AM, David Goodell (dgoodell) <dgood...@cisco.com> >> wrote: >> >>> On Jul 18, 2013, at 8:06 AM, Ralph Castain <r...@open-mpi.org> wrote: >>> >>>> That's a good point, and a bad behavior. IIRC, it results from the MPI >>>> Forum's adoption of the MPI-T requirement that stipulates we must allow >>>> access to all control and performance variables at startup so they can be >>>> externally seen/manipulated. >>> >>> Minor nit: MPI_T does not require this. However, it does recommend that >>> you offer users access to as many variables as possible as early as >>> reasonably possible for the convenience and control of the user. >>> >>> If an implementation chooses to offer 5% of the possible >>> control/performance variables to the user just before MPI_Finalize, that's >>> still a valid MPI_T implementation. But it may not be a very useful one... >> >> The problem here is one of use vs startup performance. George is quite >> correct with his concerns - this behavior would have been a serious problem >> for RoadRunner, for example, where we had a small IO channel feeding a lot >> of nodes. It will definitely become an issue at exascale where IO bandwidth >> and memory will be at a premium. > > My point was not that the performance concerns were unfounded. Rather, I > wanted to point out that the "load everything" behavior is not a hard > requirement from the MPI standard, so we have room for different > implementation choices/tradeoffs. I understood - I was more just pointing out the potential performance issue of load everything. However, Nathan has addressed it by pointing out that the problem is my aged, fading memory. > > -Dave > > > _______________________________________________ > devel mailing list > de...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/devel
