Re: [Xen-users] Xen Performance

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Sun, May 24, 2009 at 12:12:23PM +0200, Amir Maqbool Ahmed wrote:
> Hi 
> 
> I am a student at the University College of Oslo and have in one experiment 
> tried to test the performance of Xenolinux compared to Native linux on Debian 
> lenny
> 2.6.26-2 kernel. 
> 
> bonnie++ the disk IO bechmark program was used among other tests like cpu 
> intensive scripts.
> The goal is to prove the statement (Once again) that Xen adds only an 
> overhead of maximum 8%.
> 
> The Results of bonnie++ have been surprizing and I want to explain them. 
> It shows that for some types of Disk IO, like sequential delete and random 
> create
> Xen performs faster than native linux. A full comparison chart is attached as 
> a pdf.
> The test are run first from native linux than both from Dom0 and a DomU with 
> the same results.
> 
> Can you please help me understand these results, How can Xenolinux perform 
> faster 
> although only for some types of operations, then native linux?
> 
> Plese forgive me If Im missing something completely obvious. 
> If you need any further info. please just send me an email and it will be 
> provided.
> 
> Hope to hear from you soon 
> 

Hi,

Usually this is caused by using file backed disks for domU, so dom0
kernel file cache is giving this boost..

Change to LVM volumes or tap:aio instead of file, because they don't have
dom0 (file) caching..

-- Pasi

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