IBM 990 - Manual (Page 61)

Chapter 2. System structure and design 49
The CFCC command DYNDISP controls the Dynamic CF Dispatching (use DYNDISP ON to
enable the function). For more information, see 7.2.7, “Dynamic CF dispatching and dynamic
ICF expansion” on page 168.
zSeries Application Assist Processors
The zSeries Application Assist Processor (zAAP) is a PU that is used exclusively for running
Java application workloads under z/OS. One CP must be installed with or prior to any zAAP
being installed. The number of zAAPs in a machine cannot exceed the number of CPs plus
unassigned CPs in that machine. Within the capacity of the sum of all unassigned PUs in up
to four books, up to 16 zAAPs can be characterized, depending on the z990 model. Up to four
zAAPs can be characterized per book. You need an IBM 2084 model D32 with a total of 16
assigned and unassigned CPs to assign 16 zAAPs.
Within the limit of all non-characterized PUs available in the installed configuration, zAAPs
can be concurrently added to an existing configuration via Capacity Upgrade on Demand
(CUoD), Customer Initiated Upgrade (CIU), On/Off Capacity on Demand (On/Off CoD), but
zAAPs
cannot be assigned via CBU.
With On/Off CoD, you may concurrently install temporary zAAP capacity by ordering On/Off
CoD Active zAAP features up to the number of current zAAPs that are permanently
purchased. Also, the total number of On/Off CoD Active zAAPs plus zAAPs cannot exceed
the number of On/Off Active CPs plus the number of CPs plus the number unassigned CPs
on a z990 server.
For more information about CUoD, CIU, or On/Off CoD, see Chapter 8, “Capacity upgrades”
on page 187. If the installed books have no unassigned PUs left, the assignment of the next
zAAP may require the installation of an additional book.
PUs characterized as zAAPs within a configuration are grouped into the ICF/IFL/zAAP
processor pool. The ICF/IFL/zAAP processor pool appears on the hardware console as ICF
processors. The number of ICFs shown is the sum of IFL, ICF, and zAAP processors on the
server.
zAAPs are orderable by feature code (FC 0520). Up to one zAAP can be ordered for each CP
or unassigned CP configured in the machine.
zAAPs and LPAR definitions
zAAP processors can be defined as dedicated or shared processors in a logical partition and
are always related to CPs of the same partition. For a logical partition image, both CPs and
zAAPs logical processors are either dedicated or shared.
Purpose of a zAAP
zAAPs are designed for z/OS Java code execution. When Java code must be executed (that
is, under control of Websphere), the z/OS Java Virtual Machine (JVM) calls the function of the
zAAP. The z/OS dispatcher then suspends the JVM task on the CP it is running on and
dispatches it on an available zAAP. After the Java application code execution is finished, the
z/OS dispatcher redispatches the JVM task on an available CP, after which normal processing
is resumed. This reduces the CP time needed to run WebSphere applications, freeing
capacity for other workloads.
Important: The zAAP is a specific example of an assist processor that is known
generically as an Integrated Facility for Applications (IFA). The generic term IFA often
appears in panels, messages, and other online information relating to the zAAP.