Solaris Resource Manager 1.3 System Administration Guide

Scheduler Advantages

The primary advantage of the Solaris Resource Manager SHR scheduler over the standard Solaris scheduler is that it schedules users or applications rather than individual processes. Every process associated with an lnode is subject to a set of limits. For the simple case of one user running a single active process, this is the same as subjecting each process to the limits listed in the corresponding lnode. When more than one process is attached to an lnode, as when members of a group each run multiple processes, all of the processes are collectively subject to the listed limits. This means that users or applications cannot consume CPU at a greater rate than their entitlements allow, regardless of how many concurrent processes they run. The method for assigning entitlements as a number of shares is simple and understandable, and the effect of changing a user's shares is predictable.

Another advantage of the SHR scheduler is that while it manages the scheduling of individual threads (technically, in Solaris, the scheduled entity is a lightweight process (LWP)), it also apportions CPU resources between users.

These concepts are illustrated by the following equation:

Equation shows that new Solaris Resource Manager priority equals current priority plus CPU usage divided by number of shares.

The new_SRM_priority is then mapped to the system priority. The higher the Solaris Resource Manager priority, the lower the system priority, and vice versa. Every decay period, CPU_usage is reduced by half and incremented with the most current usage.

Each user also has a set of flags, which are boolean-like variables used to enable or disable selective system privileges, such as login. Flags can be set individually per user, or be inherited from a parent lnode.

A user's usages, limits, and flags can be read by any user, but they can be altered only by users with the correct administrative privileges.