Scaling System Load

To select the queue to run a job, the grid engine system uses the system load information on the machines that host queue instances. This queue selection scheme builds up a load-balanced situation, thus guaranteeing better use of the available resources in a cluster.

However, the system load may not always tell the truth. For example, if a multi-CPU machine is compared to a single CPU system, the multiprocessor system usually reports higher load figures, because it probably runs more processes. The system load is a measurement strongly influenced by the number of processes trying to get CPU access. But multi-CPU systems are capable of satisfying a much higher load than single-CPU machines. This problem is addressed by processor-number-adjusted sets of load values that are reported by default by sge_execd. Use these load parameters instead of the raw load values to avoid the problem described earlier. See Load Parameters and the sge-root/doc/load_parameters.asc file for details.

Another example of potentially improper interpretation of load values is when systems have marked differences in their performance potential or in their price performance ratio. In both cases, equal load values do not mean that arbitrary hosts can be selected to run a job. In this situation, the administrator should define load scaling factors for the relevant execution hosts and load parameters. See Configuring Execution Hosts With QMON, and related sections.

The scaled load parameters are also compared against the load threshold lists load-thresholds and migr-load-thresholds. See the queue_conf(5) man page for details.

Another problem associated with load parameters is the need for an application-dependent and site-dependent interpretation of the values and their relative importance. The CPU load might be dominant for a certain type of application that is common at a particular site. By contrast, the memory load might be more important for another site and for the application profile to which the site's compute cluster is dedicated. To address this problem, the grid engine system enables the administrator to specify a load formula in the scheduler configuration file sched_conf. See the sched_conf(5) man page for more details. Site-specific information on resource usage and capacity planning can be taken into account by using site-defined load parameters and consumable resources in the load formula. See the sections Adding Site-Specific Load Parameters) and Consumable Resources.

Finally, the time dependency of load parameters must be taken into account. The load that is imposed by the jobs that are running on a system varies in time. Often the load, for example, the CPU load, requires some amount of time to be reported in the appropriate quantity by the operating system. If a job recently started, the reported load might not provide an accurate representation of the load that the job has imposed on that host. The reported load adapts to the real load over time. But the period of time in which the reported load is too low might lead to an oversubscription of that host. The grid engine system enables the administrator to specify load adjustment factors that are used in the scheduler to compensate for this problem. See the sched_conf(5) man page for detailed information on how to set these load adjustment factors.

Load adjustments are used to virtually increase the measured load after a job is dispatched. In the case of oversubscribed machines, this helps to align with load thresholds. If you do not need load adjustments, you should turn them off. Load adjustments impose additional work on the scheduler in connection with sorting hosts and load thresholds verification.

To disable load adjustments, on the Load Adjustment tab of the Scheduler Configuration dialog box, set the Decay Time to zero, and delete all load adjustment values in the table. See Changing the Scheduler Configuration With QMON.