Good idea :)! среда, 7 мая 2014 г. пользователь Ralph Castain написал:
> Jeff actually had a useful suggestion (gasp!).He proposed that we separate > the PMI-1 and PMI-2 codes into separate components so you could select them > at runtime. Thus, we would build both (assuming both PMI-1 and 2 libs are > found), default to PMI-1, but users could select to try PMI-2. If the PMI-2 > component failed, we would emit a show_help indicating that they probably > have a broken PMI-2 version and should try PMI-1. > > Make sense? > Ralph > > On May 7, 2014, at 8:00 AM, Ralph Castain <r...@open-mpi.org> wrote: > > > On May 7, 2014, at 7:56 AM, Joshua Ladd <jladd.m...@gmail.com> wrote: > > Ah, I see. Sorry for the reactionary comment - but this feature falls > squarely within my "jurisdiction", and we've invested a lot in improving > OMPI jobstart under srun. > > That being said (now that I've taken some deep breaths and carefully read > your original email :)), what you're proposing isn't a bad idea. I think it > would be good to maybe add a "--with-pmi2" flag to configure since > "--with-pmi" automagically uses PMI2 if it finds the header and lib. This > way, we could experiment with PMI1/PMI2 without having to rebuild SLURM or > hack the installation. > > > That would be a much simpler solution than what Artem proposed (off-list) > where we would try PMI2 and then if it didn't work try to figure out how to > fall back to PMI1. I'll add this for now, and if Artem wants to try his > more automagic solution and can make it work, then we can reconsider that > option. > > Thanks > Ralph > > > Josh > > > On Wed, May 7, 2014 at 10:45 AM, Ralph Castain <r...@open-mpi.org> wrote: > > Okay, then we'll just have to develop a workaround for all those Slurm > releases where PMI-2 is borked :-( > > FWIW: I think people misunderstood my statement. I specifically did *not* > propose to *lose* PMI-2 support. I suggested that we change it to > "on-by-request" instead of the current "on-by-default" so we wouldn't keep > getting asked about PMI-2 bugs in Slurm. Once the Slurm implementation > stabilized, then we could reverse that policy. > > However, given that both you and Chris appear to prefer to keep it > "on-by-default", we'll see if we can find a way to detect that PMI-2 is > broken and then fall back to PMI-1. > > > On May 7, 2014, at 7:39 AM, Joshua Ladd <jladd.m...@gmail.com> wrote: > > Just saw this thread, and I second Chris' observations: at scale we are > seeing huge gains in jobstart performance with PMI2 over PMI1. We > *CANNOT*loose this functionality. For competitive reasons, I cannot provide > exact > numbers, but let's say the difference is in the ballpark of a full > order-of-magnitude on 20K ranks versus PMI1. PMI1 is completely > unacceptable/unusable at scale. Certainly PMI2 still has scaling issues, > but there is no contest between PMI1 and PMI2. We (MLNX) are actively > working to resolve some of the scalability issues in PMI2. > > Josh > > Joshua S. Ladd > Staff Engineer, HPC Software > Mellanox Technologies > > Email: josh...@mellanox.com > > > On Wed, May 7, 2014 at 4:00 AM, Ralph Castain <r...@open-mpi.org> wrote: > > Interesting - how many nodes were involved? As I said, the bad scaling > becomes more evident at a fairly high node count. > > On May 7, 2014, at 12:07 AM, Christopher Samuel <sam...@unimelb.edu.au> > wrote: > > > -----BEGIN PGP SIGNED MESSAGE----- > > Hash: SHA1 > > > > Hiya Ralph, > > > > On 07/05/14 14:49, Ralph Castain wrote: > > > >> I should have looked closer to see the numbers you posted, Chris - > >> those include time for MPI wireup. So what you are seeing is that > >> mpirun is much more efficient at exchanging the MPI endpoint info > >> than PMI. I suspect that PMI2 is not much better as the primary > >> reason for the difference is that mpriun sends blobs, while PMI > >> requires that everything b > > -- С Уважением, Поляков Артем Юрьевич Best regards, Artem Y. Polyakov
