Scheduler Methodology

Each lnode is assigned a number of CPU shares. The processes associated with each lnode are allocated CPU resources in proportion to the total number of outstanding active shares (active means that the lnode has running processes attached). Only active lnodes are considered for an allocation of the resource, because only they have active processes running and need CPU time.

As a process consumes CPU ticks, the CPU usage attribute of its lnode increases. The scheduler regularly adjusts the priorities of all processes to force the relative ratios of CPU usages to converge on the relative ratios of CPU shares for all active lnodes at their respective levels. In this way, users can expect to receive at least their entitlements of CPU service in the long run, regardless of the behavior of other users.

The scheduler is hierarchical because it also ensures that groups receive their group entitlements independently of the behavior of the members. Solaris Resource Manager SHR scheduler is a long-term scheduler; it ensures that all users and applications receive a fair share over the course of the scheduler term. This means that when a light user starts to request the CPU, that user will receive commensurately more resource than heavy users until their comparative usages are in line with their relative "fair" share allocation. The more you use over your entitlement now, the less you will receive in the future.

Additionally, Solaris Resource Manager has a decay period, set by the system administrator, that does not track past usage. The decay model is one of half-life decay, where 50 percent of the resource has been decayed away within one half-life. This ensures that steady, even users are not penalized by short-term, process-intensive users. The half-life decay period sets the responsiveness, or term, of the scheduler; the default value is 120 seconds. A long half-life favors even usage, typical of longer batch jobs, while a short half-life favors interactive users. Shorter values tend to provide more even response across the system, at the expense of slightly less accuracy in computing and maintaining system-wide resource allocation. Regardless of administrative settings, the scheduler tries to prevent resource starvation and ensure reasonable behavior, even in extreme situations.