Administering Platform LSF - SAS

Controlling Processor Allocation Across Hosts
Chapter 34
Running Parallel Jobs
Sometimes you need to control how the selected processors for a parallel job
are distributed across the hosts in the cluster.
You can control this at the job level or at the queue level. The queue
specification is ignored if your job specifies its own locality.
Specifying parallel job locality at the job level
Syntax
By default, LSF will allocate the required processors for the job from the
available set of processors.
A parallel job may span multiple hosts, with a specifiable number of processes
allocated to each host. A job may be scheduled on to a single multiprocessor
host to take advantage of its efficient shared memory, or spread out on to
multiple hosts to take advantage of their aggregate memory and swap space.
Flexible spanning may also be used to achieve parallel I/O.
You are able to specify “select all the processors for this parallel batch job on
the same host”, or “do not choose more than n processors on one host” by
using the span section in the resource requirement string (bsub -R or
RES_REQ in the queue definition in lsb.queues).
Two kinds of span string are supported:
◆ span[hosts=1]
Indicates that all the processors allocated to this job must be on the same
host.
◆ span[ptile=value]
Indicates the number of processors (value) on each host that should be
allocated to the job.
where value is:
❖
❖
Default ptile value, specified by n processors. For example:
span[ptile=4]
LSF allocates 4 processors on each available host, regardless of how
many processors the host has.
Predefined ptile value, specified by ’!’. For example:
span[ptile='!']
uses the predefined maximum job slot limit in lsb.hosts (MXJ per
host type/model) as its value.
If the host or host type/model does not define MXJ, the default predefined
ptile value is 1.
❖
Predefined ptile value with optional multiple ptile values, per host
type or host model.
Administering Platform LSF 441