[Xen-devel] Re: poor domU VBD performance.

[peter bier <peter_bier@xxxxxx>]

Ian Pratt <m+Ian.Pratt <at> cl.cam.ac.uk> writes:

> 
> > I found out that dom0 does file-system IO and raw IO ( using 
> > dd as a tool to test
> > throughput from the disk ) is about exactly the same as when 
> > using a standard 
> > linux kernel without XEN. But the raw IO from DomU to an 
> > unused disk ( a second
> > disk in the system ) is limited to fourty percent of the 
> > speed I get within Dom0.
> 
> Just to be clear: you're doing a dd performance test within dom0 to the
> exact same partition on the 2nd disk that you're using when you start
> the domU and finding that the domU 'dd' performance is 40% of the dom0
> performance?
> 
> I've not heard of anyone else having problems like this. What happens if
> you use a partition on the 1st disk?
> 
> What chipset is the IDE controller? What device (e.g. sda1) are you
> exporting the disk partition into the domU as?
> 
> Are you sure dom 0 is idle when doing the dd test in the domU?
> 
> Ian
> 
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Yes I do the performance testing using dd. It's only a simple "benchmark" but
its results seem to indicate
a fundamental issue. I did the tests with the same partitions from DOM0 just as
DomU. I used both disks
and Dom0 achieved in all experiments 2.5 times the transfer rate of DomU.

I do not know the chipset of my IDE controller on my computer at home, while I
know that in the office it
pas a Promise raid controller ( I am neither at home nor in the office
momentarily ) . I am sure, that the
system was idle during all test ( meaning that there was only the standard
system running with no busy
jobs and no user program consuming CPU or IO resources.

I am very interested about Xen, but I need to fiy that problem.
If there is any "checklist" how to configure XEN efficiently, I might be able to
fix the problem myself

Thanks

Peter Bier 


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