Re: [Xen-ia64-devel] [RFC][PATCH] [RESEND] support special guest optimisations in the hypervisor

[Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxxxxxxx>]

Am Mittwoch, 4. Juli 2007 schrieb Xu, Anthony:
> >From: Dietmar Hahn [mailto:dietmar.hahn@xxxxxxxxxxxxxxxxxxx]
> >Sent: 2007年7月3日 16:02
> >To: Alex Williamson
> >Cc: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx; Xu, Anthony
> >I had a look at this code (didn't do this before because I have no vti
> >machine). Everywhere GOS_WINDOWS() is currently used a opt_feature can be
> >used.
> >First question: Should we add 2 opt_features, one for both region 4 and
> > region 5, or one for each.
> >Second question: would having arguments to this feature calls make sense?
>
> GOS_WINDOWS is used for HVM, it is not convenient for HVM to use hypercall.
> At least, I don’t know where to put this hypercall inside guest OS, we
> can't modify it .
> For domU and dom0, it is preferred to use hypercall.
>
> While if there is only xenolinux running on domU and dom0, I think there is
> no need to add this hypercall, Xen and xenlinux are cooperative, so you can
> add any linux-specific optimizations.
>
> If you want to run other OSes on domU and dom0, it is preferred to use
> hypercall, I think letting xen know which OS is running on is enough, thus
> you can add any optimizations for this OS at any time. I prefer the method
> Alex mentioned that calls set_os_type hypercall at very beginning of guest
> OS boot.
>
> Using __HYPERVISOR_opt_feature is Ok for me,
> While if you find new place where you can optimize, you need to modify
> structure xen_ia64_opt_feature, and call __HYPERVISOR_opt_feature several
> times in xeno linux.

I'am not sure I understand you right. So let us clarify that.
As far as I understand Alex right, the idea was to use the opt_feature stuff 
in the HVM too. But the invocation is done in set_os_type(). There the 
function domain_opt_feature() is called to switch on the special 
region-4/region-5 identity mapping opt_feature if the guest is windows.
Therewith the hypervisor knows and uses only opt_features to switch on/off 
special optimization features for special guests, the same way on PV or HVM.
For this we must extend the opt_feature vector with the region-4/region-5 
identity mapping.
On PV the invocation is done via the __HYPERVISOR_opt_feature hypercall.
Do I see something wrong here?

Dietmar.

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