Re: [Qemu-devel] [RFC v0 0/2] Enforce gaps between DIMMs

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Tue, Oct 06, 2015 at 10:08:16AM +0200, Igor Mammedov wrote:
> On Mon, 5 Oct 2015 23:24:33 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Mon, Oct 05, 2015 at 02:05:22PM +0530, Bharata B Rao wrote:
> > > The suggested way to work around the virtio bug reported here
> > > 
> > > http://lists.nongnu.org/archive/html/qemu-devel/2015-08/msg00522.html
> > > 
> > > is to introduce gaps between DIMMs. Igor's patchset changes the pc-dimm
> > > auto-address assignment to introduce gaps and ues the same from pc memhp.
> > > This patchset does the same for sPAPR PowerPC.
> > > 
> > > Before introducing the gap, ensure that memory hotplug region has enough
> > > room for alignment adjustment. We accommodate a max alignment of 256MB for
> > > each slot since sPAPR memory hotplug enforces an alignment requirement of
> > > 256MB on RAM size, maxmem and NUMA node mem sizes.
> > > 
> > > This applies on David's spapr-next branch + Igor's patchset applied.
> > > 
> > > This has been very lightly tested and intention is to get feedback
> > > on the correctness aspect of this.
> > > 
> > > Bharata B Rao (2):
> > >   spapr: Accommadate alignment gaps in hotplug memory region
> > >   spapr: Force gaps between DIMM's GPA
> > 
> > PC needs this, PPC needs this ... I don't see why would this not
> > apply everywhere. Isn't it time we just converted everyone?
> > Drop the gap flag, set it unconditionally for new machine types.
> I guess that flag is needed exactly for compatibility with old
> machine types which are per board thingy.
> 
> BTW:
> does PPC have machine types? I don't see any compatibility
> code in this series?

For PPC, memory hotplug support starts from machine type pseries-2.5
which is the latest and hence we haven't had a need to be compatible
with any other machine type till now.

Regards,
Bharata.