> On Aug 19, 2016, at 4:24 PM, r...@open-mpi.org wrote: > > Hi folks > > I had a question arise regarding a problem being seen by an OMPI user - has > to do with the old bugaboo I originally dealt with back in my LANL days. The > problem is with an app that repeatedly hammers on a collective, and gets > overwhelmed by unexpected messages when one of the procs falls behind.
I did some investigation on roadrunner several years ago and determined that the user code issue coll/sync was attempting to fix was due to a bug in ob1/cksum (really can’t remember). coll/sync was simply masking a live-lock problem. I committed a workaround for the bug in r26575 (https://github.com/open-mpi/ompi/commit/59e529cf1dfe986e40d14ec4d2a2e5ef0cea5e35) and tested it with the user code. After this change the user code ran fine without coll/sync. Since lanl no longer had any users of coll/sync we stopped supporting it. > I solved this back then by introducing the “sync” component in ompi/mca/coll, > which injected a barrier operation every N collectives. You could even “tune” > it by doing the injection for only specific collectives. > > However, I can no longer find that component in the code base - I find it in > the 1.6 series, but someone removed it during the 1.7 series. > > Can someone tell me why this was done??? Is there any reason not to bring it > back? It solves a very real, not uncommon, problem. > Ralph This was discussed during one (or several) tel-cons years ago. We agreed to kill it and bring it back if there is 1) a use case, and 2) someone is willing to support it. See https://github.com/open-mpi/ompi/commit/5451ee46bd6fcdec002b333474dec919475d2d62 . Can you link the user email? -Nathan _______________________________________________ devel mailing list devel@lists.open-mpi.org https://rfd.newmexicoconsortium.org/mailman/listinfo/devel
