Re: [Xen-devel] pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-10-06 at 10:34 +0100, Andrew Cooper wrote:
> On 06/10/15 10:32, Andrew Cooper wrote:
> > On 06/10/15 10:11, Roger Pau Monnà wrote:
> > > El 06/10/15 a les 10.56, Ian Campbell ha escrit:
> > > > On Tue, 2015-10-06 at 08:33 +0200, Juergen Gross wrote:
> > > > > Do we have any requirements to be compatible to old releases
> > > > > regarding
> > > > > the functions in tools/python/xen/lowlevel/xc/xc.c ?
> > > > IMHO, no.
> > > > 
> > > > There are also too many compatibility shims in front of the domain
> > > > builder,
> > > > i.e. all the stuff in tools/libxc/xc_dom_compat_linux.c which IMHO
> > > > could be
> > > > nuked too.
> > > > 
> > > > > Especially pyxc_linux_build() isn't used anywhere in the tree.
> > > > > And this
> > > > > is the only function setting xc_dom_image.superpages, thus
> > > > > removing it
> > > > > would give us the chance to remove some code of the domain
> > > > > builder.
> > > > Right. 
> > > > 
> > > > Removing the superpages option from the non-Python might cause
> > > > concern for
> > > > some. Adding Konrad since IIRC PV superpages is a thing Oracle
> > > > implemented
> > > > and might still care about.
> > > > 
> > > > Also adding Roger since he is reworking the HVM builder to use the
> > > > PV one,
> > > > which for all I know might involve using the superpage option (but
> > > > probably
> > > > not the PV code to set it up).
> > > The superpages field is only used to populate memory of PV domains,
> > > AFAICT HVM domains will already try to use superpages by default in
> > > order to fill the p2m. I don't have any problem with it being
> > > removed.
> > There is a key difference between PV guests and HVM guests when it
> > comes
> > to superpages.
> > 
> > A PV guest needs to be explicitly capable of handling superpages, and
> > it
> > rules out things like migrate, etc.
> > 
> > HVM superpages are just EPT/NPT superpages, without a direct effect on
> > guest.
> > 
> > I don't object to removing this field, but mistakenly equate PV and HVM
> > guests in this regard.
> 
> Apologies.  "but don't mistakenly"

Nobody was, the question was whether we could safely remove the superpages
option from the PV dom builder API given that the HVM builder was in the
process of being folded into it.

Roger explained that superpages are effectively non-optional for an HVM
guest (as in you can't ask not to have them, because why would you) so
there is no need to retain the interface for that purpose.

Ian.


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel