Advanced POWER Virtualization on IBM System p5 - Previous ...

When PLM is notified that a partition has entered the requestor state, it will look
for resources in the following order:
► Free pool of un-allocated resources.
► A resource donor.
►
A partition with fewer shares for the requested resource that has more
resources than specified by the value of its guaranteed configurable.
If there are resources available in the free pool, they will be given to the
requestor. If there are no resources in the free pool, the list of resource donors is
checked. If there is a resource donor, the resource is moved from a donor to the
requester. The amount of resource moved is the minimum of the delta values for
the two partitions, or the amount that would give them equal priority as specified
by the policy. If there are no resource donors, the list of partitions with more
resources than their guaranteed tunable is checked.
Determining which node is more or less deserving of resources is done by
comparing how much of any resource a partition owns relative to its priority as
specified by the number of shares. PLM calculates a ranking of partitions,
including the requesting partition, from the list of partitions with excessive
resources. A partition's priorities is defined as the following ratio:
( current_amount – guaranteed_amount)
priority = -----------------------------------------------------------------------------------------------
shares
A lower value for this ratio represents a higher priority; partitions with lower value
of priority can take resources from partitions with a higher value.
Figure 6-3 on page 377 shows an overview of the process for CPU resources in
three partitions. Partition 3, under load, is a requestor. There are no free
resources in the free pool, and there are not any donor partitions. PLM looks for
partitions with excess resources (more resources than their guarantee). Both the
other partitions in the group have excess resources. Partition 1 has the highest
excess-to-shares ratio of all three partitions and resources will be moved from
partition 1 to partition 3.
376 <strong>Advanced</strong> <strong>POWER</strong> <strong>Virtualization</strong> on IBM System p5