LSF Version 7.3 - Administering Platform LSF

Administering Platform LSF 411
Reserving Resources
Time-based slot reservation vs. greedy slot reservation
With time-based reservation, a set of pending jobs will get future allocation and an
estimated start time, so that job can be placed in the future. Reservations are made
based on future allocation to guarantee estimated start time.
Start time and future allocation
The estimated start time for a future allocation is the earliest start time when all
considered job constraints are satisfied in the future. There may be a small delay of
a few minutes between the job finish time on which the estimate was based and the
actual start time of the allocated job.
If a job cannot be placed in a future allocation, the scheduler uses greedy slot
reservation to reserve slots. Existing LSF slot reservation is a simple greedy
algorithm:
◆ Only considers current available resources and minimal number of requested
job slots to reserve as many slots as it is allowed
◆ For multiple exclusive candidate host groups, scheduler goes through those
groups and makes reservation on the group that has the largest available slots
◆ For estimated start time, after making reservation, scheduler sorts all running
jobs in ascending order based on their finish time and goes through this sorted
job list to add up slots used by each running job till it satisfies minimal job slots
request. The finish time of last visited job will be job estimated start time.
Reservation decisions made by greedy slot reservation will not have an accurate
estimated start time or information about future allocation. The calculated job start
time used for backfill scheduling is uncertain, so
bjobs displays:
Job will start no sooner than indicated time stamp
Time-based reservation and greedy reservation compared
Start time prediction Time-based reservation Greedy reservation
Backfill scheduling if free
slots are available
Yes Yes
Correct with no job
topology
Yes Yes
Correct for job topology
requests
Yes No
Correct based on resource
allocation limits
Yes (guaranteed if only two
limits are defined)
No
Correct for memory
requests
Yes No
When no slots are free for
reservation
Yes No
Future allocation and
reservation based on
earliest start time
Yes No
bjobs displays best
estimate
Yes No
bjobs displays predicted
future allocation
Yes No