Other Benchmarks
Finally we compare the result for the standard unixbench benchmark in different setups.
In this case, the host is a clear winner with the guest with hugepages support and virtio driver coming in second. Looking at the details of the unixbench results shows that the host is a clear winner when it comes to the various file copying tests.This is in contrast with the bonnie++ tests where the host wasn’t even faster than the guests.
The effect of disabling hugepages for the guest is approximately 10% in this benchmark. Surprisingly, the IDE disk emulation also comes relatively close in this benchmark.
Next up is a kernel compilation with 8 threads. I am using 8 threads here to make sure that the processor is completely busy and because there is a slight performance increase compared to using only 4 threads on my quad core hyperthreading CPU.
In this case the host loses. This is probably due again to the additional caching provided by the host for each guest which effectively speeds up the guests. The guest with hugepages is in this case again the fastests of all guest configuration and IDE emulation is again not that bad compared to the bonnie++ benachmarks. Apparently, write performance is not a dominating factor for a kernel compile. In this test also, hugepages provide a performance benefit (in this case 7%).
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Great post indeed, Thank you very much.
It’s been days since I’ve been reading through lots of pages, including IBM’s library, on this subject and I must say this is a nice, well written and comprehensive article that summarize them all!
Thanks again.
Thanks for you comments. I started to look at KVM because I had a lot of issues with opensource XEN, including compatibility with display drivers, and stability problems.
I have been using KVM now since December 2010 and I must say I am really satisfied. No issues whatsoever with this technology. At the moment I am running 4 virtual machines, where 3 of them are always running and I haven’t experienced any significant issues at all.
One thing I learned recently is that with an LVM based setup, with VMs running straight from a logical volume, you should use native IO and disable caching. Especially the native IO can reduce workload on your host system. Although the workload is a bit artificial sometimes it is nice to have a workload value on the host which is never much higher than that on the guests combined. These settings are also the default on RHEL 6.2 and Centos 6.2.
It is also interesting to know that recent linux kernels (and also the custom ones shipped with Centos/RHEL 6.2) have a feature called ‘transparent hugepages’ which eliminates the need to configure anything special for hugepages.
Yeah, I noticed that transparent haugepages on Ubuntu Server 12.04.
Thanks for the heads up too, appreciate it.