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Re: [Xen-users] Why pv-on-hvm drivers?

To: Markus Schuster <ml@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Why pv-on-hvm drivers?
From: Pasi Kärkkäinen <pasik@xxxxxx>
Date: Sun, 5 Sep 2010 03:13:30 +0300
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On Sun, Sep 05, 2010 at 01:29:19AM +0200, Markus Schuster wrote:
> Hi list, 
> I've read about recent efforts to push pv-on-hvm drivers to Linux mainline 
> and I'm curious to know the cause for this. What's the advantage over using 
> pv_ops directly and booting the kernel paravirtualized?
> Are there plans to move Linux domUs closer to the KVM way (from an 
> architectural point of view)?
> Hope you can help. 

Some operating systems might be easier to install as Xen HVM guests..

The other point is performance: 32bit PV (paravirtualized) guests
perform OK, but 64bit PV guests have a performance hit if your
workload creates a lot of new processes in the guest.

HVM helps there; 64bit Linux guests might be faster as HVM,
depending on the workload.

When running Xen HVM guests you obviously need PV-on-HVM drivers,
otherwise the disk/net IO will be really slow.

So that's why Xen developers are upstreaming the PV-on-HVM drivers now..
to make it easy for every distro to ship the Xen PV-on-HVM drivers in the future
when they're included automatically in the upstream Linux kernel (starting from 
Linux 2.6.36).

-- Pasi

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