Intel 170 Servers User Manual

Linux on iSeries expands the iSeries platform solutions portfolio by allowing customers and software
vendors to port existing Linux applications to the iSeries with minimal effort.  But, how does it shape up
in terms of performance?  What does it look like generally and from a performance perspective?  How
can one best configure an iSeries machine to run Linux?  

y

"Linux is Linux."  Broadly speaking, Linux on iSeries has the same tools, function, look-and-feel of
any other Linux.

y

Linux operates in its own independent partition, though it has some dependency on OS/400 for a few
key services like IPL ("booting").

y

Virtual LAN and Virtual Disk provide differentiation for iSeries Linux.

y

Shared Processors (fractional CPUs) provides additional differentiation.

y

Linux on iSeries provides a mechanism to port many UNIX and Linux applications to iSeries.

y

Linux on iSeries particularly permits Linux-based middleware to exploit OS/400 function and data in
a single hardware package.

y

Linux on iSeries is available on selected iSeries hardware (see IBM web site for details).

y

Linux is not dependent per se on OS/400 releases.  Technically, any Linux distribution could be
hosted by any of the present two releases (V5R1 or V5R2) that allow Linux.  It becomes a question of
service and support.  Users should consult product literature to make sure there is support for their
desired combination.

y

Linux and other Open Source tools are almost all constructed from a single Open Source compiler
known as gcc.  Therefore, the quality of its code generation is of significant interest.  Java is a
significant exception to this, having its own code generation.

For various technical reasons, Linux may only be deployed on systems with certain hardware facilities.

These are:

y

Logical partitioning (LPAR).  Linux is not part of OS/400.  It needs to have its own partition of the
system resources, segregated from OS/400 and, for that matter, any other Linux partitions.  A special
software feature called the Hypervisor keeps each partition operating separately.

y

“Guest” Operating System Capability.  This begins in V5R1.  Part of the iSeries Linux freedom
story is to run Linux as Linux, including code from third parties running with root authority and other
privilege modes.  By definition, such code is not provided by IBM.  Therefore, to keep OS/400 and
Linux segregated from each other, a few key hardware facilities are needed that are not present on
earlier models.  (When all partitions run OS/400, the hypervisor’s task is simplified, permitting older
iSeries and AS/400 to run LPAR).

In addition, some models and processor feature codes can run Linux more flexibly than others.  The two
key features that not all Linux-capable processors support are:

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

©

 Copyright IBM Corp. 2008