Platform LSF Administration Guide Version 6.2

Host Selection
Administering Platform LSF
72
Host Selection
Each time LSF attempts to dispatch a job, it checks to see which hosts are eligible to run
the job. A number of conditions determine whether a host is eligible:
◆ Host dispatch windows
◆ Resource requirements of the job
◆ Resource requirements of the queue
◆ Host list of the queue
◆ Host load levels
◆ Job slot limits of the host.
A host is only eligible to run a job if all the conditions are met. If a job is queued and
there is an eligible host for that job, the job is placed on that host. If more than one host
is eligible, the job is started on the best host based on both the job and the queue
resource requirements.
Host load levels
A host is available if the values of the load indices (such as r1m, pg, mem) of the host are
within the configured scheduling thresholds. There are two sets of scheduling
thresholds: host and queue. If any load index on the host exceeds the corresponding
host threshold or queue threshold, the host is not eligible to run any job.
Viewing host load
levels
◆ Use the bhosts -l command to display the host thresholds.
◆ Use the bqueues -l command to display the queue thresholds.
Eligible hosts
When LSF tries to place a job, it obtains current load information for all hosts.
The load levels on each host are compared to the scheduling thresholds configured for
that host in the
Host section of lsb.hosts, as well as the per-queue scheduling
thresholds configured in
lsb.queues.
If any load index exceeds either its per-queue or its per-host scheduling threshold, no
new job is started on that host.
Viewing eligible
hosts
The bjobs -lp command displays the names of hosts that cannot accept a job at the
moment together with the reasons the job cannot be accepted.
Resource requirements
Resource requirements at the queue level can also be used to specify scheduling
conditions (for example,
r1m<0.4 && pg<3).
A higher priority or earlier batch job is only bypassed if no hosts are available that meet
the requirements of that job.
If a host is available but is not eligible to run a particular job, LSF looks for a later job
to start on that host. LSF starts the first job found for which that host is eligible.