Martin and myself took our argument off-list over a few virtual beers. I still owe you the outcome of that.
* CPU time accounting in Linux is *different* with later kernels (from SLES10 / RHEL5 on) The older kernels used TOD clock (wall clock based) where the newer kernels use the CPU timer (virtual CPU time based). These measure entirely different things and it is not very relevant whether one of them is more accurate or more precise than the other. Whether one metric is *better* than the other depends on what you want to measure. Either approach hides some aspects of virtualization and reveals others. Martin and myself seem to want different metrics. Without knowing what you want to measure, you can't tell which one is better. * Understanding of performance problems requires both Linux and z/VM data Full understanding of any performance problems with Linux on z/VM will normally require that you combine z/VM metrics with Linux statistics. For z/VM metrics you need a performance monitor. For Linux the kernel provides the metrics for various measurement tools. * Using *top* on SLES10 / RHEL5 Since "top" uses the metrics provided by the kernel, it will also show different numbers based on the new CPU timer accounting when used on later kernels. Depending on the configuration, it may point you in the right direction when a Linux server is using excessive resources. But that still does not make "top" a monitoring tool, for example because its heavy resource consumption actually disturbs the system you try to measure. * Two kernel problems caused incorrect CPU usage accounting in Linux Martin says the bad numbers we noticed in our test case would be corrected by fixes that are in the pipeline. The impact of an ill-behaving application (like in our case) would also be mitigated by these fixes. I have to take his word for it, since I have not been able to verify it. The fixes for these problems will over time show up in your favorite Linux distribution. 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
