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Re: [Xen-users] Xen and KVM.

To: echo@xxxxxxxxxxxx
Subject: Re: [Xen-users] Xen and KVM.
From: "Grant McWilliams" <grantmasterflash@xxxxxxxxx>
Date: Wed, 19 Nov 2008 08:15:43 -0800
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On Wed, Nov 19, 2008 at 1:25 AM, Tim Post <echo@xxxxxxxxxxxx> wrote:
Hi Grant,

On Tue, 2008-11-18 at 22:31 -0800, Grant McWilliams wrote:
>         KVM has around half the context-switches per packet/block
>         transmitted
>         than Xen, even PV Xen.
>         --
>         Javier
> Do you happen to know how Xen can do a Gb going out the interface but
> only 360Mb coming in?

This is (at least) partly due to Xennet acceleration if your talking
about PV guests in general.

If your using network adapters with tcp offload and iSCSI, part of that
bump is due to the hardware, can you describe your hardware and speedup?


   I'm talking PV on CentOS 5.2 Dom0 and CentOS 5.2 DomUs. I'm using Xen 3.3. The machine has Intel Gb/E cards and nothing special. I wanted to benchmark some VMs of various kinds and I noticed that DomU to DomU performance sat at about 360Mb/sec which seemed way off the mark so then I tested DomU to Dom0 and got about 800Mb/sec. After further testing is seems that if the traffic is exiting the DomU then it goes full speed but there's a slowdown  when data is entering the DomU. I'm not sure this is the whole story though as I've seen people on this list set up real network cards for each DomU claiming that the performance is better.

Grant McWilliams

Some people, when confronted with a problem, think "I know, I'll use Windows."
Now they have two problems.

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