Fairshare Job Priority ExampleConsider the following information associated with calculating the fairshare factor for job X.
In this example, the Fairshare component calculation would be as follows:
Priority += 100 * (
User A is 5% below his target so fairshare increases the total fairshare factor accordingly. Group B has no target so group fairshare usage is ignored. Account C is above its 10% above its fairshare usage target so this component decreases the job's total fairshare factor. QOS D is 15% over its target but the '+' in the target specification indicates that this is a 'floor' target, only influencing priority when fairshare usage drops below the target value. Thus, the QOS D fairshare usage delta does not influence the fairshare factor.
Fairshare is a great mechanism for influencing job turnaround time via priority to favor a particular distribution of jobs. However, it is important to realize that fairshare can only favor a particular distribution of jobs, it cannot force it. If user X has a fairshare target of 50% of the machine but does not submit enough jobs, no amount of priority favoring will get user X's usage up to 50%.
See the Fairshare Overview for more information.
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