[Xen-devel] Re: Xen: Hybrid extension patchset for hypervisor

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 16/09/2009 10:08, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx> wrote:

> The principle is okay I guess. These changes would have to be trickled in
> with a  really good explanation and justification for each one. For example,
> I'm not clear why the enable-hybrid hypercall is needed. Why not just
> provide access to evtchn and timer hypercalls always, and guest sues them if
> it is capable of it? I'm also not sure why PV timer events get routed to
> irq0 -- why not via an event channel as usual, now that you are enabling HVM
> guests to use the evtchn subsystem? What's a hybrid gnttab, and why does it
> need an explciit reserved e820 region? And so on.
> 
> The general principle of these patches seems to be to create a set of
> individual, and perhaps largely independent, accelerations/enlightenments to
> the HVM interface. I can at least agree with and support that aim.

By the way, if your intention is to speed up 64-bit guest performance, then
I think you should compare with running a full PV guest in a VMCS container.
That is runs in VMX non-root mode but still retains the usual full-PV
interfaces. I think that would be no more code than you are proposing here,
and would avoid scattering a bunch more code around the guest OS, to which
there is bound to be resistance.

 -- Keir



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