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

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Jeremy Fitzhardinge wrote on Thu, 17 Sep 2009 at 10:34:51:

> On 09/17/09 08:56, Nakajima, Jun wrote:
>> I thought pv_xxx_ps (such as pv_time, pv_cpu_ops, pv_mmu_ops, etc.)
> was designed to choose the right pv_ops accordingly depending on the
> features available.
>> 
>  Sure.  It would be easy to either use new special-purpose just plain
> native versions of those ops if that's the right thing to do; but it
> would be nice if a current unmodified PV guest worked within a HVM
> container and got at least some benefit from doing so.  Also, pagetable
> issues have repercussions beyond just the raw pagetable update functions.
> 
> Of course you can get both these features just by booting the kernel as
> an hvm guest.  But if we're talking about giving PV kernels some
> benefits from hvm/hap hardware features, I think we should looking at it
> from the perspective of starting with a PV kernel then adding
> incremental changes.
> 

Even if we start from PV kernels, I think what we should do is to implement 
ability (as "incremental changes") for PV guests to stop using PV MMU (and PV 
CPU) at boot time depending on the H/W features available rather than to keep 
using the same ABI, because we may not need them in the near future. Then, such 
PV kernels would be at par or faster/more efficient than pure HVM guests on 
machines with HAP enabled because of the other PV features. 

Jun
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Intel Open Source Technology Center




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