There is a fair amount of confusion, and some disagreement in this area. I would not just add QUICKDSP to all my guests. However, there are three types of guests that should have QUICKDSP set ON: 1. Any server virtual machine that is key to operation of the system (Barton describes this as 'an extension of the operating system'). This includes your security manager, accounting, file servers, etc. 2. Critical guests- My definition: any guest that if it were to stop running for a period of time could result in someone being fired. 3. The VM userid you use to do tuning (so if you make a mistake you can undo it).
The QUICKDSP setting exempts the virtual machine from having to sit time out in the eligible list. It does not exempt the virtual machine from being dropped from the dispatch list. Relative share and absolute share usage can also be a religious discussion. Relative is convenient because you can use it to give a 'relatively' higher priority without needing to necessarily understand actual resources consumed (though that helps). That is Relative 2000 virtual machine would have 20 times better access to resources than default Relative 100 share virtual machine. Now, using Absolute share requires a bit more planning upfront, but it can be necessary for certain guests. Remember Relative share is relative to which virtual machines are competing for resources. So with Relative share, as the number of competing virtual machines increases, the effective priority of a relative share virtual machine decreases. This may not be what you want. A little more discussion on this occurs at http://www.vm.ibm.com/perf/tips/linuxper.html with some links to more details. That covers the major options that can be set in the VM directory. The other command (sorry can't be set in directory) that you might want to be familiar with is CP SET RESERVE to give some favoritism of memory for a guest. I haven't seen it needed in many Linux z/VM environments, but it is worth knowing about it. Bill Bitner - VM Performance Evaluation - IBM Endicott - 607-429-3286 ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
