2014-05-08 5:54 GMT+07:00 Ralph Castain <r...@open-mpi.org>: > Ummm....no, I don't think that's right. I believe we decided to instead > create the separate components, default to PMI-2 if available, print nice > error message if not, otherwise use PMI-1. > > I don't want to initialize both PMIs in parallel as most installations > won't support it. >
Ok, I agree. Beside the lack of support there can be a performance hit caused by PMI1 initialization at scale. This is not a case of SLURM PMI1 since it is quite simple and local. But I didn't consider other implementations. On May 7, 2014, at 3:49 PM, Artem Polyakov <artpo...@gmail.com> wrote: > > We discussed with Ralph Joshuas concerns and decided to try automatic PMI2 > correctness first as it was initially intended. Here is my idea. The > universal way to decide if PMI2 is correct is to compare PMI_Init(.., > &rank, &size, ...) and PMI2_Init(.., &rank, &size, ...). Size and rank > should be equal. In this case we proceed with PMI2 finalizing PMI1. > Otherwise we finalize PMI2 and proceed with PMI1. > I need to clarify with SLURM guys if parallel initialization of both PMIs > are legal. If not - we'll do that sequentially. > In other places we'll just use the flag saying what PMI version to use. > Does that sounds reasonable? > > 2014-05-07 23:10 GMT+07:00 Artem Polyakov <artpo...@gmail.com>: > >> That's a good point. There is actually a bunch of modules in ompi, opal >> and orte that has to be duplicated. >> >> среда, 7 мая 2014 г. пользователь Joshua Ladd написал: >> >>> +1 Sounds like a good idea - but decoupling the two and adding all the >>> right selection mojo might be a bit of a pain. There are several places in >>> OMPI where the distinction between PMI1and PMI2 is made, not only in >>> grpcomm. DB and ESS frameworks off the top of my head. >>> >>> Josh >>> >>> >>> On Wed, May 7, 2014 at 11:48 AM, Artem Polyakov <artpo...@gmail.com> >>> wrote: >>> >>>> 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 >>>> >>>> _______________________________________________ >>>> >>>> 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/2014/05/14716.php >>>> >>> >>> > > > -- > С Уважением, Поляков Артем Юрьевич > Best regards, Artem Y. Polyakov > _______________________________________________ > 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/2014/05/14725.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/2014/05/14726.php > -- С Уважением, Поляков Артем Юрьевич Best regards, Artem Y. Polyakov
