HP-UX Workload Manager User's Guide

Configuring WLM
Tuning the metrics and the SLOs
Chapter 5 231
smaller than number_of_shares. Similarly, when the
difference is greater than 10%, the adjustment is
proportionally larger than number_of_shares.
The larger number_of_shares is, the larger will be
adjustments made by WLM to the workload’s CPU
allocation are. This generally produces faster
convergence on the SLO goal.
If WLM changes allocations too rapidly, resulting in
instability, decrease number_of_shares. If WLM
changes allocations too slowly, increase
number_of_shares.
With absolute CPU units enabled
(absolute_cpu_units = 1), your number_of_shares
maintains more predictable behavior from your
workload regardless of the number of available cores.
Without absolute CPU units, the effect of a given
number_of_shares depends on the number of available
cores, which could produce undesirable effects. HP
recommends enabling absolute CPU units.
Tuning the goal buffer (optional)
WLM attempts to meet a goal that is slightly different from the goal you
specify in your configuration. By working toward this goal, WLM has a
buffer to work within—and small fluctuations in the service level do not
result in SLO violations.
You can specify the percentage size of this buffer with the cntl_margin
tunable. This tunable is optional and can be used in global,
metric-specific, and metric/SLO-specific tune structures.
The cntl_margin tunable syntax is:
cntl_margin = margin_value;
where
margin_value
Is a floating-point value between 0 and 1 (inclusive)
indicating a percentage distance away from the SLO’s
goal. The default value is 0.1, or 10%.