5.1.1 Priority Overview

Maui's prioritization mechanism allows component and subcomponent weights to be associated with many aspects of a job so as to enable fine-grained control over this aspect of scheduling. To allow this level of control, Maui uses a simple priority-weighting hierarchy where the contribution of each priority subcomponent is calculated as

<COMPONENT WEIGHT> * <SUBCOMPONENT WEIGHT> * <PRIORITY SUBCOMPONENT VALUE>

Each priority component contains one or more subcomponents as described in the Priority Component Overview. For example, the Resource component consists of Node, Processor, Memory, Swap, Disk, and PE subcomponents. While there are numerous priority components and many more subcomponents, a site need only focus on and configure the subset of components related to their particular priority needs. In actual usage, few sites use more than a small fraction (usually 5 or less) of the available priority subcomponents. This results in fairly straightforward priority configurations and tuning. By mixing and matching priority weights, sites may generally obtain the desired job-start behavior. At any time, the diagnose -p command can be issued to determine the impact of the current priority-weight settings on idle jobs. Likewise, the command showgrid can assist the admin in evaluating priority effectiveness on historical system usage metrics such as queue time or expansion factor.

As mentioned above, a job's priority is the weighted sum of its activated subcomponents. By default, the value of all component and subcomponent weights is set to 1 and 0 respectively. The one exception is the QUEUETIME subcomponent weight which is set to 1. This results in a total job priority equal to the period of time the job has been queued, causing Maui to act as a simple FIFO. Once the summed component weight is determined, this value is then bounded resulting in a priority ranging between 0 and MAX_PRIO_VAL which is currently defined as 1000000000 (one billion). In no case will a job obtain a priority in excess of MAX_PRIO_VAL through its priority subcomponent values.

Using the setspri command, site admins may adjust the base calculated job priority by either assigning a relative priority adjust or an absolute system priority. A relative priority adjustment will cause the base priority to be increased or decreased by a specified value. Setting an absolute system priority, SPRIO, will cause the job to receive a priority equal to MAX_PRIO_VAL + SPRIO, and thus guaranteed to be of higher value than any naturally occurring job priority.