Re: [Xen-devel] How to detect HAP from DomU?

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 11/10/10 09:44, Jiang, Yunhong wrote:
> > -----Original Message-----
> > From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> > [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Juergen Gross
> > Sent: Wednesday, November 10, 2010 4:43 PM
> > To: Keir Fraser
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] How to detect HAP from DomU?
> >
> > On 11/10/10 09:36, Keir Fraser wrote:
> > > On 10/11/2010 08:22, "Juergen Gross"<juergen.gross@xxxxxxxxxxxxxx>   wrote:
> > >
> > > > is there any way for a HVM-domain to detect whether it is running with HAP
> > > > enabled? I couldn't find any interface for this information.
> > > >
> > > > Background: in our BS2000 domain (HVM with PV-drivers) we sometimes have to
> > > > copy complete pages between kernel and user. An alternative to the copy
> > > > would be a remapping of the page. The remap is faster than the copy with HAP
> > > > enabled, but much slower without HAP. So it would be best to copy without HAP
> > > > and remap with HAP.
> > > You could do a few remaps and copies and see how long it takes? Has the
> > > advantage that you aren't tied up to one policy based on one system's
> > > timings for those particuler ops. I don't think basing policy on static
> > > assumptions about hidden implementation features is a good idea.
> > Okay, that's a good idea.
> > I'm going this way.
> Will this works for Live Migration? After LM, your previous check will be 
> invalid. (Can we migrate between system w/wo HAP?)
> Or you can check after each LM.
The same problem applies to a decision based on information supplied by the
hypervisor.
I'll have to reconsider the decision in any case, dynamical testing just takes
some microseconds more, but is more flexible.


Juergen

--
Juergen Gross                 Principal Developer Operating Systems
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