On Tue, Sep 27, 2011 at 7:06 PM, Therrian, James <[email protected]> wrote: > There is application being developed here running Message Broker on z/LINUX. > During many of the tests the distributed guys are focusing on "SYSTEM LOAD" > and it's value during our tests. While the tests seem to be running > acceptable they are still concerned about the system load value. Can someone > help in explaining what metrics go into the SYSTEM LOAD value and the how to > interpret differences of that value between zlinux and linux/unix if there > are any? >
The probably refer to "load average" which is the number of processes that run or would be able to run. The easy math is that for an N-way guest, the load average larger than N means that processes wait to get CPU resources. Since CPU resources are often the most expensive part, it's good to wait for CPU rather than something else. If your load average is lower than N, there's no CPU waiting as far as Linux is concerned. You probaby already expected me to say you can't really make sense of the numbers unless you combine it with the z/VM metrics. And it's true. When the guest is already having a hard time competing for real CPU resources for its N virtual CPUs, then trying to compete with N+1 virtual CPUs does not help you at all. It actually gets worse because Linux dispatches work on virtual CPUs under the assumption that they will run. When the Linux has many virtual CPUs that rarely run, it has much less control over which process actually runs. Even though it appears to the Linux admin that load average is < N so no problem... Plus your overhead goes up. You don't want more virtual CPUs than the resources you expect it to get when it wants them. Load average may reveal that it would like to have more. It's business decision whether it can have more. Rob -- Rob van der Heij Velocity Software http://www.velocitysoftware.com/ ---------------------------------------------------------------------- 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 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
