> > It's mostly not very useful. It reflects only the usage when the virtual > machine is dispatched. I/O counts are "mostly" OK in that it's a reflection of > virtual I/O requests (does not reflect that CP may have done something > smart with the I/O to make it more efficient -- think about VDISKs for a > moment). Memory usage is from the perspective of inside the virtual > machine (doesn't reflect impact on the total machine). > > You dismiss CPU usage too quick as "mostly" OK - while vague, probably still > not useful.
You missed a period there. "mostly OK" in that sentence applied to I/O counts, not CPU. I actually didn't comment on CPU at all. Wrt to top and CPU, it's less wrong on I/O than it is on CPU, but top is still probably somewhat wrong on I/O (see comment about reflecting only virtual I/O counts). The only useful measure in top related to CPU (IMHO) is proportionally how much of the kernel workload is allocated to which virtual processors *inside* the virtual machine. Which tells you pretty much nothing useful unless your application is massively multi-threaded and you want to know if threads are getting dispatched on all available processors. > * Most people using "top" don't really care about what they use, but about > what they don't use. The assumption is that what you don't use is still > available to use. But not in a virtualized environment... My original point (and statement): Top is mostly not very useful. > You can't have it all, and in this case you can't have either of them. > For the full picture you need a performance monitor that combines data > from inside and outside the virtual machine. Agreed. You need data from both perspectives. Top sees only one perspective. Also true on any other virtualized architecture (POWER domains, Solaris zones, VMWare, Xen, etc, etc, etc). ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu 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/
