Re: [PATCH RFC 1/2] linux/vnuma: vnuma support for pv guest

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Aug 29, 2013 at 03:32:13PM +0100, George Dunlap wrote:
> On 29/08/13 15:23, Konrad Rzeszutek Wilk wrote:
> >On Thu, Aug 29, 2013 at 02:41:23PM +0100, David Vrabel wrote:
> >>On 29/08/13 01:11, Matt Wilson wrote:
> >>>I think it wouldn't be too hard to construct the static ACPI tables
> >>>and provide them in acpi_os_get_root_pointer().
> >>Elena's approach looks fine to me from a Linux point of view.
> > From an maintaince perspective the question is:
> >
> >  - Why not re-use existing code? As in, if both PV and HVM can use
> >    SRAT, why not do it that way? This way you are exercising the same
> >    code path in both guests and it means less bugs to chase.
> >
> >    Incidententaly this also means that the mechanism to fetch the
> >    NUMA information from the hypervisor and construct the SRAT tables
> >    from can be done the same in both hvmloader and Linux kernel.
> 
> If the SRAT tables are built by hvmloader for HVM guests, couldn't
> hvmloader make this hypercall and construct the tables, instead of
> having the domain builder do it?  That would mean that most of the
> codepath is the same; HVM just has the extra step of encoding and
> decoding the information in SRAT form.

Correct. Or the domain builder can build it for both PV and HVM.

We do have the full control of E820 for PV - so can make an "E820_ACPI"
region and stash the ACPI tables.

Either way would work. Whichever one means more code sharing is probably
the best bang for the buck to say.
> 
> >>If you posted Xen and Linux series producing/using the ACPI SRAT and
> >>SLIT tables for dom0 and domU PV guests we could better evaluate that
> >>option but until then I'm inclined to consider Elena's approach as the
> >>better one.
> >I think short term Elena's option is better one as it gets it going and
> >we can experiement with it. Long term I think stashing the data in ACPI
> >SRAT/SLIT is right. But Elena might not get to it in the next couple of
> >months - which means somebody else will have to sign up for that.
> 
> I definitely think that Elena needs to continue on the same path for
> now, so she can actually have closure on the project in a reasonable
> amount of time.

I concur. The caveat is that it could mean that the x86 maintainers might
object to the generic path having the special case for Xen and that
particular patch part won't be upstreamed until it has been taken care of.

If Elena is OK with that possiblity  - then that is fine with me.