HP-UX Workload Manager User's Guide

Understanding how PRM manages resources
How resource allocations interact
Appendix F 453
Multiple users accessing raw devices (raw logical volumes) will tend to
spend most of their time seeking. The overall throughput on this group
will tend to be very low. This degradation is not due to PRM’s disk
bandwidth management.
When performing file system accesses, you need approximately six disk
bandwidth consumers in each workload group before I/O scheduling
becomes noticeable. With two users, you just take turns. With four, you
still spend a lot of your time in system call overhead relative to the peak
device bandwidth. At six, PRM disk bandwidth management begins to
take effect. The more demand you put on the system, the closer the disk
bandwidth manager approaches the specified values for the shares.
How resource allocations interact
You can assign different numbers of shares for core, memory, and disk
bandwidth to a workload group depending on the group’s requirements
for each type of resource. To optimize resource use, it is important to
understand the typical demands for resources within a workload group.
For example, suppose the DesignTool application is assigned to workload
group DTgroup, and it is the only application running in that group.
Suppose also that the DesignTool application uses CPU resources and
memory in an approximate ratio of 2 to 3. For optimal results, assign the
resource shares for DTgroup in the same ratio. For example, assign 10
CPU shares and 15 memory shares or 20 CPU shares and 30 memory
shares.
If the percentages assigned do not reflect actual usage, then a workload
group may not be able to fully utilize a resource to which it is entitled.
For instance, assume you assign 50 CPU shares and 30 memory shares
to DTgroup. At times of peak system load, DTgroup is able to use only
approximately 20 CPU shares (although it is assigned 50 shares) because
it is limited to 30 memory shares. (Recall that DesignTool uses CPU
resources and memory at a ratio of 2 to 3.) Conversely, if DTgroup is
assigned 10 CPU shares and 30 memory shares, then at times of peak
system load, DTgroup is only able to utilize 15 memory shares (not its 30
shares), because it is restricted to 10 CPU shares.