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Status Not under consideration
Workspace AIX
Created by Guest
Created on Apr 22, 2022

New values for vpm_throughput_core_threshold (enabling a more dynamic setting of the threshold).

Currently, we set SMT and vpm_throughput_mode on many LPARs. In a few cases, we use vpm_throughput_mode_threshold - set to match the entitled cores (small LPARs) or to one less than entitled cores for larger LPARs. We limit the use vpm_throughput_mode_threshold to special cases, in part, because we need to change the value when we change the size of the LPAR. Enable an additional value (for example '0' or 'E') for the vpm_throughput_core_threshold parameter. This value will set the threshold to the number of entitled (curr_proc_units) cores. Enable an additional value (for example '-1') for the vpm_throughput_core_threshold parameter. This value will set the threshold to the one less than the number of entitled cores. With these new, available values, we will not need to change the value for the vpm_throughput_core_threshold parameter when we change the size of the LPAR (expansion; reduction after migration to newer class processor, etc.). If an LPAR boots with less than the desired entitlement, the vpm_throughput_core_threshold will adjust accordingly.
Idea priority Medium
  • Guest
    Jul 26, 2022
    Please re-submit this request once the requested questions have been addressed.
  • Guest
    May 24, 2022
    We are reviewing this request and would like to know more about the request. Please see below.

    There are two parts to this request:

    Part 1
    Enable an additional value (for example '0' or 'E') for the vpm_throughput_core_threshold parameter. This value will set the threshold to the number of entitled (curr_proc_units) cores.

    Are you aware that there is a ???0" value for vpm_throughput_core_threshold?

    # schedo -h vpm_throughput_core_threshold
    Help for tunable vpm_throughput_core_threshold:
    Purpose:
    Determines the number of cores to unfold in raw throughput mode before
    switching to scaled throughput mode.
    Values:
    Default: 1
    Range: 0 - 1920
    Type: Dynamic
    Unit: cores
    Tuning:
    This parameter determines the number of cores that will be unfolded in raw
    throughput mode before switching to the specified scaled throughput mode.
    In raw throughput mode more cores are unfolded when only the primary thread
    of each unfolded core is busy. In scaled throughput mode, more cores are
    unfolded only when the desired level of SMT exploitation has been reached
    on the unfolded cores. This parameter can be used to achieve faster un-
    folding up to a desired number of cores before entering scaled throughput
    mode.

    >>> A special value of zero can be specified to affect raw throughput mode up
    >>> to the number of cores required to meet the entitled capacity of the
    >>> partition. This parameter is only applicable when vpm_throughput_mode is
    >>> non-zero.

    We believe this may satisfy your needs.

    Can you please confirm or let us know if you have more questions on this part?


    Part 2
    Enable an additional value (for example '-1') for the vpm_throughput_core_threshold parameter. This value will set the threshold to the one less than the number of entitled cores.

    This sounds like an auto N-1 mode for the threshold which automatically sets the value to the number of entitled cores -1 and ensures that as the LPAR grows/shrinks (across dynamic add/remove operations or reboots) that the current number of assigned cores is reflected in the real-time setting used by AIX virtual processor management decisions. This is similar to the special setting of ???0" described above which keeps the number of entitled cores unfolded at N for the partition. (N = # of currently assigned entitled cores for the LPAR).

    We are interested to know why you think LPARs do better with N-1 unfolded cores before switching to higher throughput modes?