Administering Platform LSF - SAS

Chapter 14
Fairshare Scheduling
Accumulated slots
in use
As queues run the jobs allocated to them, LSF accumulates the slots each queue
has used and decays this value over time, so that each queue is not allocated
more slots than it deserves, and other queues in the pool have a chance to run
their share of jobs.
Interaction with other scheduling policies
Examples
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Queues participating in a queue-based fairshare pool cannot be
preemptive or preemptable.
You should not configure slot reservation (SLOT_RESERVE) in queues that
use queue-based fairshare.
Cross-queue fairshare (FAIRSHARE_QUEUES) can undo the dispatching
decisions of queue-based fairshare. Cross-queue fairshare queues should
not be part of a queue-based fairshare pool.
◆ Three queues using two hosts each with maximum job slot limit of 6 for a
total of 12 slots to be allocated:
❖ queue1 shares 50% of slots to be allocated = 2 * 6 * 0.5 = 6 slots
❖ queue2 shares 30% of slots to be allocated = 2 * 6 * 0.3 = 3.6 -> 4 slots
❖ queue3 shares 20% of slots to be allocated = 2 * 6 * 0.2 = 2.4 -> 3 slots;
however, since the total cannot be more than 12, queue3 is actually
allocated only 2 slots.
◆ Four queues using two hosts each with maximum job slot limit of 6 for a
total of 12 slots; queue4 does not belong to any pool.
❖ queue1 shares 50% of slots to be allocated = 2 * 6 * 0.5 = 6
❖ queue2 shares 30% of slots to be allocated = 2 * 6 * 0.3 = 3.6 -> 4
❖ queue3 shares 20% of slots to be allocated = 2 * 6 * 0.2 = 2.4 -> 2
❖ queue4 shares no slots with other queues
queue4 causes the total number of slots to be less than the total free and
in use by the queue1, queue2, and queue3 that do belong to the pool. It
is possible that the pool may get all its shares used up by queue4, and jobs
from the pool will remain pending.
◆ queue1, queue2, and queue3 belong to one pool, queue6, queue7, and
queue8 belong to another pool, and queue4 and queue5 do not belong to
any pool. LSF orders the queues in the two pools from higher priority
queue to lower priority queue (queue1 is highest and queue8 is lowest):
queue1 -> queue2 -> queue3 -> queue6 -> queue7 -> queue8
If the queue belongs to a pool, jobs are dispatched from the highest priority
queue first. Queues that do not belong to any pool (queue4 and queue5)
are merged into this ordered list according to their priority, but LSF
dispatches as many jobs from the non-pool queues as it can:
queue1 -> queue2 -> queue3 -> queue4 -> queue5 -> queue6 -> queue7 -> queue8
Administering Platform LSF 219