[Xen-users] Benchmark results

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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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