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Re: [Xen-users] Bad TCP accept performance

None of your Xen tests where performed on a suitably recent kernel... KVM was performed on kernel whereas Xen was performed on 2.6.32... Fair difference. Kernel development has been pretty active lately and I would not be surprised if you see major differences between older and newer kernels when using for virtualisation.

I'm attempting to install Xen on top of 2.6.39 vanilla kernel today. Will run your tests on my box and see what the results are...

Quite disheartening to see such a drop in accept performance, I for one hope it's just misconfiguration (or requires further configuration) to bring the VMs up to spec.


On 25 May 2011, at 08:51, Carl Byström wrote:

On Wed, May 25, 2011 at 7:54 AM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
Btw did you use 64bit or 32bit VMs? I'd suggest to try 32bit aswell if you didn't.

I've tried it on EC2, but not on our private servers yet. Made no difference there.

Someone has also suggested that increasing the backlog (well beyond 128) could help improve things.
tcp_syncookies was another suggestion. I have no idea what they will do, haven't tried them yet.

Also got a report (see the previous link posted) from someone on KVM with a lot better performance.
Whether those were correctly performed, I cannot tell but at least interesting if that's the case.

Carl Byström

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