Xen devel - Sep 2010 - Passing information from HVM to Xen hypervisor

hello,

I want to pass some information about the HVM guest kernel from the HVM
guest to the hypervisor (specifically, the scheduler). What is the best way
to implement this and how should I go about it (hypercall vs. shared page)?
I was taking a look at an old post related to a similar issue [
http://xen.1045712.n5.nabble.com/Hypercall-from-HVM-guest-td2525175.html],
but it wasn''t very conclusive.

thanks,
Priyanka


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It depends on what information you want to pass.  Shared pages are
good to pass information to Xen if it''s updated frequently, but Xen
doesn''t necessarily need to know about each update.  (Paravirtualized
TPR would be a good example of this -- updated somtimes thoundands of
times per second, but only important if Xen is delivering an
interrupt.)

For simplicity, I''d probably say start with a hypercall, and switch to
a shared page only if the overhead of making the VMEXITs is causing a
measurable performance problem.

Are you doing scheduler work?

 -George

On Thu, Sep 16, 2010 at 3:51 PM, Priyanka Tembey
<tembey.priyanka@gmail.com> wrote:
> hello,
>
> I want to pass some information about the HVM guest kernel from the HVM
> guest to the hypervisor (specifically, the scheduler). What is the best way
> to implement this and how should I go about it (hypercall vs. shared page)?
> I was taking a look at an old post related to a similar issue
> [http://xen.1045712.n5.nabble.com/Hypercall-from-HVM-guest-td2525175.html],
> but it wasn''t very conclusive.
>
> thanks,
> Priyanka
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel
>
>
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Thanks for the input, George.
Is there a starting piece of code I can look at, to add a hypercall that can
be used from within an application inside an HVM guest? I''m familiar
with
the interface between Dom0 and Xen, not so much between an HVM guest and
Xen.

I''m currently working on providing useful hints to the Xen scheduler
about
scheduling components of multi-tier applications hosted in separate virtual
machines. So the scheduler needs to be enlightened with VM group notions,
also if the application (which has more knowledge about its workings than
the hypervisor) needs to use that knowledge in scheduling itself and other
components, then the hypervisor will support scheduler extensions to do so.

thanks,
Priyanka



On Thu, Sep 16, 2010 at 11:04 AM, George Dunlap
<George.Dunlap@eu.citrix.com
> wrote:
> It depends on what information you want to pass.  Shared pages are
> good to pass information to Xen if it''s updated frequently, but
Xen
> doesn''t necessarily need to know about each update. 
(Paravirtualized
> TPR would be a good example of this -- updated somtimes thoundands of
> times per second, but only important if Xen is delivering an
> interrupt.)
>
> For simplicity, I''d probably say start with a hypercall, and
switch to
> a shared page only if the overhead of making the VMEXITs is causing a
> measurable performance problem.
>
> Are you doing scheduler work?
>
>  -George
>
> On Thu, Sep 16, 2010 at 3:51 PM, Priyanka Tembey
> <tembey.priyanka@gmail.com> wrote:
> > hello,
> >
> > I want to pass some information about the HVM guest kernel from the
HVM
> > guest to the hypervisor (specifically, the scheduler). What is the
best
> way
> > to implement this and how should I go about it (hypercall vs. shared
> page)?
> > I was taking a look at an old post related to a similar issue
> > [
> http://xen.1045712.n5.nabble.com/Hypercall-from-HVM-guest-td2525175.html],
> > but it wasn''t very conclusive.
> >
> > thanks,
> > Priyanka
> >
> >
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xensource.com
> > http://lists.xensource.com/xen-devel
> >
> >
>

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