pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Juergen Gross]

Do we have any requirements to be compatible to old releases regarding
the functions in tools/python/xen/lowlevel/xc/xc.c ?

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.


Juergen

Re: pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Ian Campbell]

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).

Also CCing the other tools/libxc maintainers.

Ian.

Re: pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Juergen Gross]

On 10/06/2015 10:56 AM, Ian Campbell wrote:
> 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.

Okay, thanks.

I'll check for other unused functions as well and do some patches to
remove it (or them) from tools/python/xen/lowlevel/xc/xc.c

> 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.

Okay, I'll look into this as well.

>> 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).

I'm starting with the layers above the domain builder. This should give
all others interested in the features some time to raise concerns about
removing them.


Juergen

Re: pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Roger Pau Monné]

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.

Roger.

Re: pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Andrew Cooper]

On 06/10/15 10:11, Roger Pau Monné 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.

~Andrew

Re: pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Andrew Cooper]

On 06/10/15 10:32, Andrew Cooper wrote:
> On 06/10/15 10:11, Roger Pau Monné 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"

~Andrew

Re: pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Ian Campbell]

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 Monné 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@lists.xen.org
http://lists.xen.org/xen-devel

Re: pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Juergen Gross]

On 10/06/2015 10:56 AM, Ian Campbell wrote:
> 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.

Hmm, all of the functions there are defined in xenguest.h and are
probably used by out-of-tree components.

xc_linux_build() is used in qemu-xen in file /hw/xenpv/xen_domainbuild.c

Is it really okay to remove all of this stuff?


Juergen

Re: pyxc_linux_build() in tools/python/xen/lowlevel/xc/xc.c still needed?

[Ian Campbell]

On Tue, 2015-10-06 at 12:56 +0200, Juergen Gross wrote:
> On 10/06/2015 10:56 AM, Ian Campbell wrote:
> > 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.
> 
> Hmm, all of the functions there are defined in xenguest.h and are
> probably used by out-of-tree components.
> 
> xc_linux_build() is used in qemu-xen in file /hw/xenpv/xen_domainbuild.c
> 
> Is it really okay to remove all of this stuff?

In general, yes, I think so. But in the specific case of xc_linux_build I
suppose not, at least for now.

As part of my series to split up libxenctrl I noticed that the QEMU support
for domain building couldn't possibly have worked (according to a code
comment) since Xen 4.1 and I've got a patch to make it a compile time
option.

Ian