Platform LSF Administration Guide Version 6.2
Job Scheduling and Dispatch
Administering Platform LSF
70
Job Scheduling and Dispatch
Submitted jobs sit in queues until they are scheduled and dispatched to a host for
execution. When a job is submitted to LSF, many factors control when and where the
job starts to run:
◆
Active time window of the queue or hosts
◆
Resource requirements of the job
◆
Availability of eligible hosts
◆
Various job slot limits
◆
Job dependency conditions
◆
Fairshare constraints
◆
Load conditions
Scheduling policies
First-Come, First-
Served (FCFS)
scheduling
By default, jobs in a queue are dispatched in first-come, first-served (FCFS) order. This
means that jobs are dispatched according to their order in the queue. Since jobs are
ordered according to job priority, this does not necessarily mean that jobs will be
dispatched in the order of submission. The order of jobs in the queue can also be
modified by the user or administrator.
Fairshare
scheduling and
other policies
If a fairshare scheduling policy has been specified for the queue or if host partitions have
been configured, jobs are dispatched in accordance with these policies instead. To solve
diverse problems, LSF allows multiple scheduling policies in the same cluster. LSF has
several queue scheduling policies such as exclusive, preemptive, fairshare, and
hierarchical fairshare.
Scheduling and dispatch
Jobs are scheduled at regular intervals (5 seconds by default, configured by the parameter
JOB_SCHEDULING_INTERVAL in
lsb.params). Once jobs are scheduled, they
can be immediately dispatched to hosts.
To prevent overloading any host, LSF waits a short time between dispatching jobs to the
same host. The delay is configured by the JOB_ACCEPT_INTERVAL parameter in
lsb.params or lsb.queues; the default is 60 seconds. If
JOB_ACCEPT_INTERVAL is set to zero, more than one job can be started on a host
at a time.
Some operating systems, such as Linux and AIX, let you increase the number of file
descriptors that can be allocated to the master host. You do not need to limit the number
of file descriptors to 1024 if you want fast job dispatching. To take advantage of the
greater number of file descriptors, you must set the parameter
LSB_MAX_JOB_DISPATCH_PER_SESSION in
lsf.conf to a value greater than
300. LSB_MAX_JOB_DISPATCH_PER_SESSION defines the maximum number of
jobs that
mbatchd can dispatch during one job scheduling session. You must restart
mbatchd and sbatchd when you change the value of this parameter for the change to
take effect.