************************* README.LVM.IO.FUNNELING ************************* 

   * Overview
   * Limitations
   * AIX Behavior Differences
   * Performance Considerations
   * Usage

========
Overview
========

The purpose of this README is to introduce a technique for funneling
IO on a per volume group basis to a particular cpu for the RS/6000
Enterprise Server M80 and the IBM eServer pSeries p680. This AIX
technique provides a performance tuning method which benefits some
workloads, regresses others, limits some system functionality.

Customers are advised to review this README in its entirety and the 
referenced White Paper before enabling this technique.

What this technique provides for is an attempt to the issuing most
of the IOs on a volume group on a specific CPU. This avoids some cache
line bounces and possibly increasing through put.


===========
Limitations
===========
1)  When this technique is enabled, unpredictable results (including system
    crashes) may occur when vendor software has built-in dependencies upon the
    number of processors in the system.

2)  This technique is not supported on UP systems nor on the
    /usr/lib/boot/unix_up kernel.

3)  This technique is only supported on Volume groups with major numbers
    less that 1024.


=========================
AIX Behavior Differences
=========================

1)  When technique is enabled the IO requests that LVM device driver issues
    will be queued to the assigned CPU. This results in a slight delay
    for individual IO requests through the LVM device driver.

==========================
Performance Considerations
==========================

In general, this technique may increase raw throughput of "heavy" Volume Group
workloads. Light workloads may see a decline in throughput when this 
technique is enabled.

=====
Usage
=====

1)  To enable this technique, issue the following command:

    cfg_hd_other VG_MAJOR CPU_NUMBER

    Where VG_MAJOR is the major number of the volume group you want to enable
    this technique on.

    Where CPU_NUMBER is the CPU number you wish to assign the VG_MAJOR to.


2)  Rebooting the machine will disable the technique.