Re: Report on Virtualization in Clusters

[Håvard Bjerke <havarbj@idi.ntnu.no>]

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On Fri, Nov 26, 2004 at 11:44:03AM +0100, Jacob Gorm Hansen wrote:
> Håvard Bjerke wrote:
> >Rune and I just finished writing a report on using virtualization with Xen 
> >in clusters, with focus on network performance. You may download it from 
> >http://www.idi.ntnu.no/~havarbj/clust_virt.pdf
> >
> >We hope you find it interesting!
> 
> Yes, very interesting. Good work.
> 
> It seems from your tests without interrupt coalescing that Xen has a 
> higher interrupt-handling overhead than native Linux.  I suppose that 
> with the new IO model, Xen needs to flush the TLBs for every interrupt 
> that arrives. Do you think this is the reason for the overhead, or are 
> the performance problems only due to your hardware being badly supported 
> by Xen?

My guess is that it is the former, because we "solved" the problem with the IOAPIC bug with 'ignorebiostables'. Thus using legacy PIC, everything seemed to behave normally except when not using IC.

I think it boils down to whether or not using legacy PIC as opposed to (a supported) IOAPIC has an impact on interrupt handling. If it does, I think it's the latter reason, otherwise I think it's the former.

It would be quite easy to verify on the other cluster. I just couldn't find out how to disable IC on the tg3 driver.

The Xen developers could probably give a better answer, though.

Håvard


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