LSF Version 7.3 - Administering Platform LSF

Administering Platform LSF 415
Reserving Resources
◆ MXJ, JL/U in lsb.hosts
◆ PJOB_LIMIT, HJOB_LIMIT, QJOB_LIMIT, UJOB_LIMIT in lsb.queues
Memory request To request memory resources, configure RESOURCE_RESERVE in lsb.queues.
When RESOURCE_RESERVE is used, LSF will consider memory and slot requests
during time-based reservation calculation. LSF will not reserve slot or memory if
any other resources are not satisfied.
If SLOT_RESERVE is configured, time-based reservation will not make a slot
reservation if any other type of resource is not satisfied, including memory requests.
When SLOT_RESERVE is used, if job cannot run because of non-slot resources,
including memory, time-based reservation will not reserve slots. For example, if job
cannot run because it cannot get required license, job will be pending without any
reservation
Host partition and queue-level scheduling
If host partitions are configured, LSF first schedules jobs on the host partitions and
then goes through each queue to schedule jobs. The same job may be scheduled
several times, one for each host partition and last one at queue-level. Available
candidate hosts may be different for each time.
Because of this difference, the same job may get different estimated start times,
future allocation, and reservation in different host partitions and queue-level
scheduling. With time-based reservation configured, LSF always keeps the same
reservation and future allocation with the earliest estimated start time.
bjobs displays future allocation information
◆ By default, job future allocation contains LSF host list and number of CPUs per
host, for example:
alloc=2*hostA 3*hostB
◆ LSF integrations define their own future allocation string to override the
default LSF allocation. For example, in RMS, future allocation is displayed as:
rms_alloc=2*sierra0 3*sierra1
Predicted start time may be postponed for some jobs
If a pending job cannot be placed in a future resource allocation, the scheduler can
skip it in the start time reservation calculation and fall back to use greedy slot
reservation. There are two possible reasons:
◆ The job slot request cannot be satisfied in the future allocation
◆ Other non-slot resources cannot be satisfied.
Either way, the scheduler continues calculating predicted start time for the
remaining jobs without considering the skipped job.
Later, once the resource request of skipped job can be satisfied and placed in a
future allocation, the scheduler reevaluates the predicted start time for the rest of
jobs, which may potentially postpone their start times.
To minimize the overhead in recalculating the predicted start times to include
previously skipped jobs, you should configure a small value for
LSB_TIME_RESERVE_NUMJOBS in
lsf.conf.