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Re: [Xen-users] Original Kernel or HVM

To: Andrey Varsavsky <alex.faq8@xxxxxxxxx>
Subject: Re: [Xen-users] Original Kernel or HVM
From: "Thaddeus J. Hogan" <thaddeus@xxxxxxxxxx>
Date: Thu, 06 Aug 2009 09:46:37 -0500
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What domU will be work faster: with basic kernel or with HVM kernel?
Here are your options for kernel selection and virtualization mode:

Virtualiztion: Paravirtualized (PV) or HVM

Kernels that work with HVM: Any unmodified kernel
Kernels that work with PV: Xen PV Kernel -OR- Unmodified kernel with PV_OPS support

IIRC PV_OPS support is now in the mainstream kernel tree. I am able to use Ubuntu 9.04 unmodified kernels in Xen PV mode.

As for which is faster, I have only used HVM a little bit to get a fresh install up before converting to PV. I though I/O was too slow in HVM mode. In HVM mode I saw about 40% of the I/O capacity I was able to obtain in PV mode. I have been running all my domUs paravirtualized since.

That said, I guess that there is some availability for Xen specific block device and network drivers that can be installed on a domU running in HVM mode. I have read that this bring I/O performance up to a level comparable with operating in PV mode. I have not tried this myself but if you want to run Windows or something else you can't paravirtualize, I would look into that.

-- Thaddeus

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