A
service class is a named group of work within a
workload with the following similar performance characteristics:
- Performance goals
- Resource requirements
- Business importance to the installation
Workload
management manages
a service class period as a single entity when allocating resources
to meet performance goals. A service class can be associated with
only one workload. You can define up to 100 service classes.
You can assign the following kinds of performance goals to
service classes: average response time, response time with percentile, velocity, and discretionary. You assign
an importance level to the performance goal. Importance indicates
how vital it is to the installation that the performance goal be met
relative to other goals.
Because some work has variable resource requirements, workload management provides performance
periods where you specify a series of varying goals and importances.
You can define up to eight performance periods for each service class.
You can also assign a service class to a resource group if its CPU
service must be either protected or limited.
This information explains the parts of a service class, how to
define performance goals, and how to use performance periods.
Defining service classes and performance goals |
- Name
- Service class name
- Description
- Service class description
- Workload
- The name of the workload associated with this service class.
- Resource Group
- The name of the resource group associated
with the work in this service class.
- Performance Period
- One goal per period.
- Duration
- Number of service units for this performance period. This value is calculated including all processor types.
- Average Response Time
- Average response time for transactions completing within the period
in terms of hours, minutes, and seconds. Decimal points are accepted.
Response time varies from 15 milliseconds to 24 hours.
- Response Time and Percentile
- A percentile of work to be completed in the specified amount of
time. Percentile boundaries vary from 1 to 99. Amount of time is in
hours, minutes, or seconds. Decimal points are accepted. Response
time ranges from 15 milliseconds to 24 hours.
- Velocity
- Measure of how fast work should run when ready, without being
delayed for WLM-managed resources. Velocity
ranges from 1 to 99.
- Discretionary
- Workload
management defined
goal. Work is run as system resources are available.
- Importance
- How important it is to the installation that the goal be achieved.
- CPU Protection
- Whether long-term CPU protection should be assigned to this service
class.
- I/O Priority Group
- Whether long-term I/O protection should be assigned to this service
class.
|
- Name (required)
- Eight characters describing the service class. Service class names
must be unique within a service definition.
- Description (optional)
- An area of 32 characters describing the service class. The descriptive
text is available to performance monitors for reporting.
- Workload (required)
- The name of the workload associated with the service class. You
can associate only one workload per service class in a service definition.
The workload must have been previously defined.
- Resource Group (optional)
- The resource group name associated with this service class. You
can assign only one resource group per
service class in a service policy. You can override the resource group assigned
to a service class in each service policy. For more information about
resource groups, see Defining resource groups.
- Performance Period
- A performance goal, importance, and duration for a service
class. You set up multiple performance periods for work that has changing
performance requirements as work consumes more and more resources.
You can specify up to eight performance periods.
- Duration
- Specifies
the length of the period in service units. For a definition of service
units, see Defining service coefficients and options. If the work included
in this service class period does not complete when the number of
service units have been used, the work moves into the next performance
period. You do not specify a duration on the last defined period.
- Response Time
- The expected amount of time required to complete the work submitted
under the service class, in milliseconds, seconds, minutes and hours.
Specify either an average response time, or response time with a percentile.
Percentile is the percentage of work in that period that should complete
within the response time. Percentile must be a whole number. You must
specify a system response time goal, not “end-to-end”. That is, workload
management does not control all aspects of system performance, so
response time scope is confined to the time workload management has control
of the work. This time includes the time the work is using or waiting
for CPU, storage, or I/O service.
Note: Workload
management does not
delay work, or limit it, to achieve the response time goal when extra
processing capacity exists.
- Velocity
- A measure of how fast work should run when ready, without being
delayed for WLM-managed resources. Velocity is a
percentage from 1 to 99. See Velocity formula for
a description of the calculations needed to determine velocity.
- Discretionary
- Workload management defined goal. Associate this goal with work
for which you do not have a specific performance goal. Work with a
discretionary goal is run when excess resources are available.
- Importance
- The relative importance of the service class goal. Importance
is a reflection of how important it is that the service class goal
be achieved, Workload
management uses
importance only when work is not meeting its goal. Importance indicates
the order in which work should receive resources when work is not
achieving its goal. Importance is required for all goal types except
discretionary. Importance applies on a performance period level and
you can change importance from period to period. Importance is in
five levels: 1 to 5, 1 being the highest importance.
- CPU Protection
- By specifying YES in the “CPU Critical” field when defining a
service class, you ensure that work of lower importance will always
have a lower dispatch priority. See Defining special protection options for critical work for
more information.
- I/O Priority Group
- By specifying HIGH in the “I/O Priority Group” field when defining
a service class, you ensure that work in this service class will always
have a higher I/O priority than work in service classes assigned to
I/O priority group NORMAL. SeeDefining special protection options for critical work for
more information.