To use the NX Accelerator, an LPAR requires so-called credits in addition to the correct processor mode. Each LPAR is automatically assigned default credits, the number depends on the LPAR’s entitlement. However, default credits do not guarantee that a hardware accelerator can actually be used. This depends, among other things, on the current utilization of the hardware accelerator. If no hardware accelerator is available, the system automatically switches to software algorithms, which means a significantly longer runtime.

In order to guarantee the availability of credits, and thus the availability of a hardware accelerator, the PowerVM administrator can assign so-called Quality of Service (QoS) credits to LPARs. A QoS credit guarantees the use of a hardware accelerator. If multiple compressions and/or decompressions must be possible in parallel with hardware accelerators, an LPAR requires a corresponding number of QoS credits.

The maximum number of QoS credits as well as the QoS credits not yet assigned to LPARs can be displayed for one or more managed systems using the “ms lsaccel” command:

$ ms lsaccel ms25 ms26
NAME  TYPE  MAX_QOS  CURR_AVAIL_QOS  PEND_AVAIL_QOS
ms25  gzip  128      96              96
ms26  gzip  256      256             256
$

The managed system ms25, for example, has a total of 128 QoS credits, of which 96 are currently available, i.e. not assigned to LPARs.

By default, an LPAR initially does not have any QoS credits. QoS credits can be assigned to an LPAR using the command “lpar chaccel”:

$ lpar chaccel aix01 5
$

Note: The prerequisite is of course that the managed system supports the use of hardware accelerators.

The number of QoS credits of an LPAR can be changed dynamically at any time. The prerequisite is an active RMC connection to the HMC.

How many QoS credits LPARs have can be displayed with the command “lpar lsaccel”:

$ lpar lsaccel aix01 aix02 aix03
LPAR_NAME  TYPE  CURR_QOS  PEND_QOS
aix01      gzip  5         5
aix02      gzip  12        12
$

Note: LPARs that do not have QoS credits are not displayed. The LPAR aix03 is not listed, so it has no QoS credits.