v4.0.x: Update the PML selection/check logic to avoid direct modex "storms" #8408
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With this patch the best PML is selected earlier, before finalizing the others PML. This provides a simpler mechanism to intercept and highjack the PML (as done in the monitoring PML) Signed-off-by: George Bosilca <bosilca@icl.utk.edu> (cherry picked from commit 668aa15) (cherry picked from commit 65fbffa)
For direct modex, all procs publish the selected pml module and then at add_procs pml module for each proc is checked against every other proc in the add_proc call. For full modex, there is no change in functionality. Only Rank0 publishes its selected pml, all other procs in the add_proc call check their selected pml against Rank0. If pml's do not match, throw error and exit. Signed-off-by: Dipti Kothari <dkothar@amazon.com> (cherry picked from commit 5418cc5) (cherry picked from commit 5de4423)
Signed-off-by: Ralph Castain <rhc@pmix.org> (cherry picked from commit 56eb572)
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I have moved this to "draft" status because I believe we need to revisit the PML selection check scheme. Please see #8404 (comment) for an explanation |
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After conversation, this is good to go! |
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bot:aws:retest |
bwbarrett
approved these changes
Jan 21, 2021
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As currently written in this release branch, the PML selection "check" logic doesn't guarantee that the caller's PML choice will be checked against only that from MPI_COMM_WORLD rank=0 when a full modex has been performed. This can lead to every process calling "dmodex" to obtain the PML selection of every other process in the job, causing major delay in wireup on first call to communicate.
These cherry-picks contain the updates developed/committed to master after the code in this release branch was brought over to it. One additional cherry-pick was required to cleanly port the code.