Re: [Xen-devel] Benchmark results

Keir Fraser
2008-08-03T17:07:39Z

If the virtual disc is a loopback-mounted file then the domU is probably
benefitting from dom0''s buffer cache (i.e., domU is happening to
exploit
dom0''s memory to cache its own data).

 -- Keir

On 3/8/08 17:51, "bbmailing@web.de" <bbmailing@web.de> wrote:

> 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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