[Xen-devel] Benchmark results

bbmailing@web.de
2008-08-03T16:51:50Z

Hey everyone,

I hope you guys can help me explaining a pretty strange result that came up when
benchmarking a native Red Hat installation against a Xen DomU (installed in a
file container). I used lmbench3 on a dualcore AMD-machine. To make the results
comparable, I "unplugged" all CPU cores but one in the native
installation (setting the "online"-entry to 0). The DomU had only one
vCPU assigned. The installed packages on both machines were identical as well.
After doing the initial configuration of lmbench3 I ran a script doing 10 times
a "make rerun".

All results seem to be OK somehow. But I cannot explain why Xen is faster than
the native installation when creating and deleting files? Its 12ms (DomU)
against 24ms (native) for creating a 0K file and 50ms (DomU) against 60ms
(native) for creating a 10K file. Please find all the results attached.

Is there any way this is possible? Maybe the communication methods used by the
shared device drivers make the virtual machine think the operation has been
finished successfully faster than the native way? Is there is anyone out there
who can help me understanding this result?

Furthermore: Is there a special recommendation for benchmarking Xen against
native installations? I liked lmbench so far since it puts the focus on basic
operations... what are your favourites? Is lmbench from a design perspective the
wrong tool to use?

I have to find some reliable results so I am really thankful for every single
hint here... please feel free to email me directly as well!

Thank you so much in advance!

Best regards,
Bjoern
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