Administering Platform LSF - SAS

How Fairshare Affects Job Dispatch Order
Chapter 14
Fairshare Scheduling
Within a queue, jobs are dispatched according to the queue’s scheduling
policy.
◆ For FCFS queues, the dispatch order depends on the order of jobs in the
queue (which depends on job priority and submission time, and can also
be modified by the job owner).
◆ For fairshare queues, the dispatch order depends on dynamic share
priority, then order of jobs in the queue (which is not necessarily the order
in which they are submitted to the queue).
A user’s priority gets higher when they use less than their fair share of the
cluster’s resources. When a user has the highest priority, LSF considers one of
their jobs first, even if other users are ahead of them in the queue.
If there are only one user’s jobs pending, and you do not use hierarchical
fairshare, then there is no resource contention between users, so the fairshare
policies have no effect and jobs are dispatched as usual.
Job dispatch order among queues of equivalent priority
Example
The order of dispatch depends on the order of the queues in the queue
configuration file. The first queue in the list is the first to be scheduled.
Jobs in a fairshare queue are always considered as a group, so the scheduler
attempts to place all jobs in the queue before beginning to schedule the next
queue.
Jobs in an FCFS queue are always scheduled along with jobs from other FCFS
queues of the same priority (as if all the jobs belonged to the same queue).
In a cluster, queues A, B, and C are configured in that order and have equal
queue priority.
Jobs with equal job priority are submitted to each queue in this order: C B A
B A.
◆ If all queues are FCFS queues, order of dispatch is C B A B A (queue A is
first; queues B and C are the same priority as A; all jobs are scheduled in
FCFS order).
◆ If all queues are fairshare queues, order of dispatch is AA BB C (queue A
is first; all jobs in the queue are scheduled; then queue B, then C).
◆ If A and C are fairshare, and B is FCFS, order of dispatch is AA B B C
(queue A jobs are scheduled according to user priority; then queue B jobs
are scheduled in FCFS order; then queue C jobs are scheduled according
to user priority)
◆ If A and C are FCFS, and B is fairshare, order of dispatch is C A A BB
(queue A is first; queue A and C jobs are scheduled in FCFS order, then
queue B jobs are scheduled according to user priority)
◆ If any of these queues uses cross-queue fairshare, the other queues must
also use cross-queue fairshare and belong to the same set, or they cannot
have the same queue priority. For more information, see “Cross-queue
Fairshare” on page 211.
Administering Platform LSF 207