Intel AS/400 RISC Server manual Linux on iSeries Technical Overview, Linux on iSeries Architecture

yShared Processors. This variation of LPAR allows the Hypervisor to use a given processor in multiple partitions. Thus, a uni-processor might be divided in various fractions between (say) three LPAR partitions. A four way SMP might give 3.9 CPUs to one partition and 0.1 CPUs to another. This is a large and potentially profitable subject, suitable for its own future paper. Imagine consolidating racks of old, under utilized servers to several partitions, each with a fraction of an iSeries CPU driving it.

yHardware Multi-tasking. This is controlled by the system-wide value QPRCMLTTSK, which, in turn, is controlled by the primary partition. Recent AS/400 and iSeries machines have a feature called hardware multi-tasking. This enables OS/400 (or, now, Linux) to load two jobs (tasks, threads, Linux processes, etc.) into the CPU. The CPU itself will then alternate execution between the two tasks if one task waits on a hardware resource (such as during a cache miss). Due to particular details of some models, Linux cannot run with this enabled. If so, as a practical matter, the entire machine must run with it disabled. In machines where Linux supports this, the choice would be based on experience -- enabling hardware multi-tasking usually boosts throughput, but on occasion would be turned off.

Which models and feature codes support Linux at all and which enable the specific features such as shared processors and hardware multi-tasking are revealed on the IBM iSeries Linux web site.

13.3 Linux on iSeries Technical Overview

Linux on iSeries Architecture

IBM i 6.1 Performance Capabilities Reference - January/April/October 2008
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