Performance Tuning WebWizard

Expanation of CPU

The CPU of your machine hardly needs any expanation but you still want to make sure that it is used effectively. In modern computer systems the CPU is the most expensive item in the system and so is the last thing to be upgraded.

The pSeries range now includes:

Uni-Processors
SMP - Symetric Multi-Processors (F50, J40/J50)
MPP - Massively Parallel Processors

These different machines need to have their CPU monitored in different ways as outlined below.

CPU Bottleneck ???

Criteria: CPU bound when %user+%sys greater than 80%

In a multi-user environment CPU usage is always likely to be very peaky - meaning that users demands of the CPU are in lots of small unpredictable bursts. To cater for this we need to keep the average CPU usage below 80% so that small peaks in workload can be handled immediately.

While monitoring CPU do not worry about small 1 to 3 seconds of 100% CPU busy but take a longer term view.

CPU monitor Statistics

The basic CPU usage is on the Main Screen of monitor.
The statisics break what the CPU is doing into 4 types of activity.

Sys System or Kernel This is running the UNIX/AIX Operating System Kernel which includes scheduling processes, file I/O, paging, device drivers and running the network.
Wait Waiting for I/O This is idle time while waiting for Disk I/O to complete.
User Applications This is user processes i.e. your applications and database programs.
Idle Nothing to do This is when the CPU has nothing to do i.e. waiting to users to request some action

Notes:

These percentages should add up to 100%
The CPU is "doing something" useful in sys and user
The CPU has "nothing to do" in wait and idle
The only difference between wait and idle is that in wait the CPU could do something useful, if the disks were faster.
Another way to view it is wait is waiting for Disk I/O and idle is waiting for users (or possibly network).

What can you do to tune CPU?

If you find the CPU is 100% busy all the time:

If this is an SMP, check all CPU's are busy - see tuning SMP.
Check we are not paging - see tuning memory.
Reducing Disk I/O means less CPU is used reading Disks - see tuning disks
Check there are no "run-away" processes - see tuning processes
Plan for an upgrade!!

Sys	System or Kernel	This is running the UNIX/AIX Operating System Kernel which includes scheduling processes, file I/O, paging, device drivers and running the network.
Wait	Waiting for I/O	This is idle time while waiting for Disk I/O to complete.
User	Applications	This is user processes i.e. your applications and database programs.
Idle	Nothing to do	This is when the CPU has nothing to do i.e. waiting to users to request some action