So I have a customer who I hold in high regard that did similar studies. She defined a 16-way linux server in something like 4 IFLs. (I thought she was crazier than normal). But results were "very good". The only thing I can think of is that the scheduler in linux is so bad, that letting the z/vm scheduler take over makes a huge difference. And most of the spin lock issues seem to be resolved in later releases of Linux. So as many things get "ROTten" when they age, so do some Rules Of Thumb when given a newer set of parameters.
Martha McConaghy wrote:
We have an interesting problem. We have a big Oracle database (part of our ERP) running on SLES 10. At the end of October, we will be doing our first full student registration with the new system, so we have been running some load tests using a program named "grinder". I'm not sure how realistic the tests are, but its what we have to work with. The system is running in an LPAR on a z9 with 3 IFLs. I have 3 virtual IFLs defined for the machine, along with 6G of memory. When they run their tests, the memory and I/O seem fine. The problem is that from the Linux point of view, the 3 virtual processors get pegged at 100% load. I can see from the CP stats that VM is running very high (cpu load), but is not at 100%. So, it seems to be the virtual processors that are throatling it. As an experiment, I moved the virtual machine over to our older z990, to an LPAR with 5 real processors. These are slower than the z9, but there is much less load overall. I defined 5 virtual processors to the virtual machine and we ran the tests again. The difference was dramatic. The virtual processors never reached their max of 100%. The throughput of the transactions was much improved. So, despite the slowness of the real processors, adding 2 more virtual processors made a big difference. My understanding has always been that you should not define more virtual processors than real processors for a virtual machine. Does this still hold when dealing with Linux guests? Does anyone have any suggestions on how to deal with the problem? I'd like to keep the server over on the z9, but I don't have any more real processors to add to the LPAR. Martha ---------------------------------------------------------------------- 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/
---------------------------------------------------------------------- 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/
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