HP-UX Workload Manager User's Guide

How WLM manages workloads
Allocating CPU resources: The rising tide model
Chapter 3122
Allocating CPU resources: The rising tide
model
If all workloads’ demand for CPU resources can be met with current
resources, WLM satisfies that demand. If however, demand exceeds
supply, WLM uses the “rising tide” model to allocate CPU resources: At a
given priority, WLM attempts to raise the allocation of the workload with
the lowest CPU allocation to the level of the next lowest allocation. If
CPU resources remain, WLM then raises the allocations for those two
groups to the level of the third lowest group. This process continues at
the current priority until all CPU resource requests have been met or all
resources have been distributed. If requests have been met and resources
remain, WLM continues with the next priority.
Consider Figure 3-2 on page 123 with groups A, B, and C. All groups start
with 1 CPU share. At priority 1, only groups A and B are requesting CPU
resources. Their requests of 15 and 25 shares are easily satisfied. WLM
meets the lowest request first, granting 14 additional shares to both
groups. WLM then grants an additional 10 shares to group B to meet its
higher request. Group C and the default group OTHERS (not shown) both
receive 1 share. After satisfying those CPU resource requests, 58 shares
are left.
At priority 2, groups A B, and C all request 60 shares. These requests, of
course, sum to 180 shares—exceeding the available 100 shares. With the
58 remaining shares, WLM can meet only one of the SLOs. With all three
SLOs at the same priority, WLM attempts to satisfy them all as much as
possible—rather than meet one SLO at the expense of the other two. The
strategy of meeting each SLO as much as possible is similar to a rising
tide lifting all boats: All workloads are raised to the same CPU
allocation.
Group C starts with 1 share. WLM first grants group C an additional 14
shares, raising its allocation to match the allocation for group A. WLM
then adds 10 shares to the allocations for both A and C, matching that of
group B. Now each group has 25 shares. The 24 remaining shares are
distributed evenly among the three groups. The last share is still being
used by the group OTHERS (not shown).