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  1. Lustre
  2. LU-9441

Use kernel threads in predictable fashion to confine OS noise

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Details

    • Improvement
    • Resolution: Fixed
    • Major
    • Lustre 2.14.0
    • None
    • None

    Description

      During benchmarking at large scale on KNL+Omnipath system (8k nodes) we saw periodic OS noise due to lustre kernel threads that greatly affects the performance of small-message MPI collectives (MPI_Barrier, MPI_Allreduce with small datasize, etc).

      The request is for lustre to use kernel threads in a deterministic manner when the load is low. In this case the ideal usage would have been to use only the thread(s) in CPT 0 which can be setup to run only on KNL tile 0 (cores 0 and 1). Then when no significant I/O is going on, a benchmark thread can be bound to a tile other than 0 and not see any lustre noise.

      This is more than just a benchmarking setting, it is common for allreduce to be a bottleneck especially at scale, and usually HPC applications have long phases with no I/O.

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              simmonsja James A Simmons
              lfmeadow Larry Meadows (Inactive)
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                Updated:
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