CPU Allocation

Bound and Unbound CPUs

With vPars, there are two types of CPUs: bound and unbound.

A bound CPU is a CPU that is assigned to and handles I/O interrupts for a virtual partition. Every virtual partition must have at least one bound CPU to handle its I/O interrupts.

CPUs that are not assigned to any virtual partition or that are assigned to a virtual partition but do not handle its I/O interrupts are unbound CPUs. Unbound CPUs are sometimes called floater CPUs.

All CPUs begin as not being assigned to any virtual partition, so all CPUs begin as unbound CPUs. Using the vPars commands, you can assign CPUs to virtual partitions as bound or unbound.

For more information on how to do this using the vPars commands, see “Adding and Removing CPU Resources”.

CPU Migration

CPU migration refers to adding CPUs to and deleting CPUs from a virtual partition. Dynamic CPU migration refers to migrating CPUs while the target virtual partition is running.

You can migrate both bound and unbound CPUs, but because HP-UX cannot dynamically migrate I/O interrupts, you can dynamically migrate only unbound CPUs.

For more information on how to migrate bound and unbound CPUs, see “Adding and Removing CPU Resources”.

Determining Whether to Use Bound or Unbound CPUs

When the applications within the target virtual partitions are I/O intensive, use bound CPUs because only bound CPUs can process I/O interrupts; specifically, with I/O intensive applications there should be more bound CPUs than unbound CPUs.

If your applications are CPU intensive (and not I/O intensive), use unbound CPUs so that you can easily adjust the number of CPUs via dynamic CPU migration as the demand on the virtual partition changes. Unbound CPUs provide greater flexibility of movement between virtual partitions because they can be added and removed without needing to bring down the affected partitions.

Determining When to Specify a Hardware Path for a Bound CPU

By default, the vPars monitor chooses the hardware path of a bound CPU. However, if you need to use a specific processor, you can specify its hardware path in the vPars commands.

Generally, you do not need to specify a hardware path. The main purpose of specifying hardware paths is when you need to consider NUMA (Non-Uniform Memory Access) factors, where the distance between a CPU and memory is critical to performance. The rp5470/L3000 and rp7400/N4000 servers do not have NUMA architectures, so there is usually no need to specify CPU hardware paths with these servers. Although the Superdome has a NUMA architecture, the HP-UX OS does not yet support the NUMA features.