The number of processors you want to add to a logical partition depends on the planned workload for the partition and the desired level of performance.
The number of processors you want to add to a logical partition depends on the planned workload for the partition and the desired level of performance. The number of partitions supported depends on the number of processors in the server model. If you are running release V5R1 or later, the 820, 830, and 840 models can have up to 32 logical partitions using the shared processor pool. The 820, 830, and 840 models are also designed to have up to 24 logical partitions using dedicated processors. The 890 model supports up to 32 logical partitions using dedicated processors.
For estimation purposes, approximately each processor of a server offers 1/(total number of processors on the server) of the total Commercial Processing Workload (CPW) performance available through that processor feature.
Refer to the Logical Partition web site for additional information on performing Capacity Planning 
for your iSeries™ server.