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Re: [Xen-devel] [PATCH 0/7][v4] PV extension of HVM (Hybrid) for Xen

To: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 0/7][v4] PV extension of HVM (Hybrid) for Xen
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Mon, 01 Mar 2010 16:42:01 -0800
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>, Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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On 03/01/2010 01:38 AM, Sheng Yang wrote:
I'd like to have your comments on this patch series. We think the patches are
prepared for check in pv_ops domU tree.

The PV extension of HVM is started from real mode like HVM guest, but also with 
a range of PV features(e.g. PV halt, PV timer, event channel, as well as PV
drivers). So guest with this feature can takes the advantages of both H/W
virtualization and Para-Virtualization.

The PV device side of this has a lot of overlap with the older PV driver for HVM domains code. Aside perhaps for the details of how interrupts/events are actually delivered, that seems like a completely distinct piece of work which could be done separately.

Also, I'd like to see a clearer statement of what you're specifically trying to optimise for here. What is inefficient in an unmodified HVM domain, and how do your patches address these things. What measurements have you made?

The first two of the patchset imported several header file from Jeremy's tree
and Xen tree, respect to Jeremy and Keir's works.

The whole patchset based on Linux upstream.

You need a line like:

cpuid = [ '0x40000002:edx=0x3' ]

in HVM configuration file to expose hybrid feature to guest, and


in the guest kernel configuration file to enable the hybrid support.

And the compiled image can be used as native/pv domU/hvm guest/pv feature hvm 

Current the patchset support x86_64 only.

Please add a new config option for the new code, and make it dependent on x86-64, rather than scattering random #ifdef CONFIG_X86_64s around the code. Make sure all the code is controlled by this CONFIG variable so it disappears in a 32-bit build (ideally by putting it into a new file where possible, and only building it when enabled).

I've discussed the vector-evtchn mapping with Stefano, and we agreed on that
it's more complex than we thought, and can't brought much benefit for
pvops domU. So there is no major change in this update.

Change from v3:
1. Rebase to Linux 2.6.33 release.

Why 2.6.33? I'm currently working on 2.6.32; I intend to move to .33 shortly, but .32 is a much more convenient base (particularly if you're interested in getting these changes into any distro kernels).

I rebased it to .32 without much effort.

I'll make specific comments in the patches.


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