Platform LSF Administration Guide Version 6.2

Chapter 28
Running Parallel Jobs
Administering Platform LSF
457
Optimized Preemption of Parallel Jobs
You can configure preemption for parallel jobs to reduce the number of jobs suspended
in order to run a large parallel job.
When a high-priority parallel job preempts multiple low-priority parallel jobs, sometimes
LSF preempts more low-priority jobs than are necessary to release sufficient job slots to
start the high-priority job.
The PREEMPT_FOR parameter in
lsb.params with the MINI_JOB keyword
enables the optimized preemption of parallel jobs, so LSF preempts fewer of the low-
priority parallel jobs.
Enabling the feature only improves the efficiency in cases where both preemptive and
preempted jobs are parallel jobs.
How optimized preemption works
When you run many parallel jobs in your cluster, and parallel jobs preempt other parallel
jobs, you can enable a feature to optimize the preemption mechanism among parallel
jobs.
By default, LSF can over-preempt parallel jobs. When a high-priority parallel job
preempts multiple low-priority parallel jobs, sometimes LSF preempts more low-priority
jobs than are necessary to release sufficient job slots to start the high-priority job. The
optimized preemption mechanism reduces the number of jobs that are preempted.
Enabling the feature only improves the efficiency in cases where both preemptive and
preempted jobs are parallel jobs. Enabling or disabling this feature has no effect on the
scheduling of jobs that require only a single processor.
Configuring optimized preemption
Use the PREEMPT_FOR parameter in lsb.params and specify the keyword
MINI_JOB to configure optimized preemption at the cluster level.
If the parameter is already set, the MINI_JOB keyword can be used along with other
keywords; the other keywords do not enable or disable the optimized preemption
mechanism.