Administering Platform LSF - SAS

Reserving Processors
Reserving Processors
About processor reservation
When parallel jobs have to compete with sequential jobs for resources, job
slots that become available are likely to be taken immediately by a sequential
job. Parallel jobs need multiple job slots to be available before they can be
dispatched. If the cluster is always busy, a large parallel job could be pending
indefinitely. The more processors a parallel job requires, the worse the
problem is.
Processor reservation solves this problem by reserving job slots as they become
available, until there are enough reserved job slots to run the parallel job.
You might want to configure processor reservation if your cluster has a lot of
sequential jobs that compete for resources with parallel jobs.
How processor reservation works
Processor reservation is disabled by default.
If processor reservation is enabled, and a parallel job cannot be dispatched
because there are not enough job slots to satisfy its minimum processor
requirements, the job slots that are currently available will be reserved and
accumulated.
A reserved job slot is unavailable to any other job. To avoid deadlock situations
in which the system reserves job slots for multiple parallel jobs and none of
them can acquire sufficient resources to start, a parallel job will give up all its
reserved job slots if it has not accumulated enough to start within a specified
time. The reservation time starts from the time the first slot is reserved. When
the reservation time expires, the job cannot reserve any slots for one
scheduling cycle, but then the reservation process can begin again.
Configuring processor reservation
Syntax
To enable processor reservation, set SLOT_RESERVE in lsb.queues and
specify the reservation time (a job cannot hold any reserved slots after its
reservation time expires).
SLOT_RESERVE=MAX_RESERVE_TIME[n].
where n is an integer by which to multiply MBD_SLEEP_TIME.
MBD_SLEEP_TIME is defined in lsb.params; the default value is 60 seconds.
Example
Begin Queue
.
PJOB_LIMIT=1
SLOT_RESERVE = MAX_RESERVE_TIME[5]
.
End Queue
In this example, if MBD_SLEEP_TIME is 60 seconds, a job can reserve job slots
for 5 minutes. If MBD_SLEEP_TIME is 30 seconds, a job can reserve job slots
for 5 *30= 150 seconds, or 2.5 minutes.
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Administering Platform LSF