Overview of dynamic MSU limit

You can use a dynamic MSU limit to specify a lower MSU limit without delaying important work for more than a short time.

You can implement a dynamic MSU limit by using the following parameters to set the MSU limit values for your policies and subpolicies: 

Related topics

How-iCap-works

iCap-PAS-started-task-parameters

Overview-of-MSU-limit-CPCMSU-limit-and-cost-limit

Parameter

Description

Initial MSULIMIT

Initial starting MSU limit

Important

In previous versions of iCap, this parameter is called MSU limit.

Max MSULIMIT

Maximum number of allowable MSUs to be consumed collectively by all LPARs and capacity groups that the policy or subpolicy manages

Inc MSULIMIT

Number of MSUs by which the initial MSU limit incrementally increases if iCap is unable to run low importance workloads

Adj MSULIMIT

Percentage of low importance work at which iCap starts to increase the MSU limit

Designates the LPARs whose low-importance work is considered when calculating the low-importance workload percentage to determine if iCap needs to increase MSU limit.

For more information, see Policy-level-and-subpolicy-level-parameters.

How a dynamic MSU limit works

After you set the required parameters for a policy or subpolicy, iCap uses the following process to run a dynamic MSU limit.

Important

To run a dynamic MSU limit, iCap must be running in manage or message mode.

  1. At startup, the master PAS uses your initial MSU limit (lowest value) or the monthly MSU limit. 
    For more information about the monthly MSU limit, see Step 3.

  2. iCap begins to increase the MSU limit when at least one LPAR or capacity group is capped, the MSU limit is approaching, and one of the following conditions exists: 

    • The policy or subpolicy cannot run low importance work.
    • The policy's or subpolicy's percentage of low importance work decreases to less than your specified Adj MSULIMIT value for LPARs with priority less than or equal to SCOPE parameter.

    Important

    iCap uses the following guidelines when dynamically increasing the MSU limit:

    • For each increment, increases the limit by the number of MSUs that the Inc MSULIMIT parameter specifies
    • In terms of frequency, increases the limit every number of minutes that the ADJTIME parameter specifies, or every five minutes if the ADJTIME value is less than 5
    • Continues increasing the limit until one of the following conditions exists:
      • The LPAR or capacity group is no longer being capped
      • The percentage of low importance work in the policy or subpolicy exceeds the specified Adjusted MSU limit percentage.
      • The policy or subpolicy reaches the maximum MSU limit.

  3. When the master PAS has an IPL, iCap saves the peak MSU limit (also called the monthly MSU limit) in the registry.

    iCap uses the monthly MSU limit the next time the master PAS starts. 

    Important

    Consider the following information:

    • If you switch the policy and the monthly MSU limit is within the policy's MSU limit range, the monthly MSU limit is used.
    • If iCap increases a subpolicy's MSU limit, the main policy's MSU limit automatically increases to allow for the additional MSUs. When the master PAS has an IPL, iCap does not save the monthly MSU limit for subpolicies. Consequently, at startup, a subpolicy always uses the initial MSU limit.
    • If you start the master PAS on another LPAR, the registry must be shared among the LPARs. Otherwise, iCap uses the initial MSU limit when the master PAS starts.

    Tips

    If the monthly MSU limit is significantly higher than the initial MSU limit, consider resetting your Initial MSULIMIT value. For example, if you remove LPARs from the policy, the additional MSUs are not required.

    If you are running in message mode iCap might increase the monthly MSU limit even though it doesn't change the DCs and GCLs or absolute capping values. If you want to switch to manage mode, consider resetting the monthly MSU limit.

    You can use a modify command to reset the monthly MSU limit to zero. After the reset, iCap adjusts the monthly MSU limit to the initial MSU limit. For more information, see Resetting-the-monthly-MSU-limit-for-the-active-policy.

    In addition, you can use a modify command to temporarily change the initial MSU limit. For more information, see Temporarily-changing-the-MSU-limits-for-the-active-policy-and-subpolicies.

  4. iCap resets the monthly MSU limit to the initial MSU limit at midnight on the second day of the month. 

    Important

    If LPARs are using multiple time zones, iCap uses Coordinated Universal Time (UTC).

 

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