- Update to 20.11.03
- This release includes a major functional change to how job step launch is
handled compared to the previous 20.11 releases. This affects srun as
well as MPI stacks - such as Open MPI - which may use srun internally as
part of the process launch.
One of the changes made in the Slurm 20.11 release was to the semantics
for job steps launched through the 'srun' command. This also
inadvertently impacts many MPI releases that use srun underneath their
own mpiexec/mpirun command.
For 20.11.{0,1,2} releases, the default behavior for srun was changed
such that each step was allocated exactly what was requested by the
options given to srun, and did not have access to all resources assigned
to the job on the node by default. This change was equivalent to Slurm
setting the --exclusive option by default on all job steps. Job steps
desiring all resources on the node needed to explicitly request them
through the new '--whole' option.
In the 20.11.3 release, we have reverted to the 20.02 and older behavior
of assigning all resources on a node to the job step by default.
This reversion is a major behavioral change which we would not generally
do on a maintenance release, but is being done in the interest of
restoring compatibility with the large number of existing Open MPI (and
other MPI flavors) and job scripts that exist in production, and to
remove what has proven to be a significant hurdle in moving to the new
release.
Please note that one change to step launch remains - by default, in
20.11 steps are no longer permitted to overlap on the resources they
have been assigned. If that behavior is desired, all steps must
explicitly opt-in through the newly added '--overlap' option.
Further details and a full explanation of the issue can be found at:
https://bugs.schedmd.com/show_bug.cgi?id=10383#c63
OBS-URL: https://build.opensuse.org/request/show/864993
OBS-URL: https://build.opensuse.org/package/show/network:cluster/slurm?expand=0&rev=171
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