Re: [libvirt] [PATCH v2 82/86] numa: forbid '-numa node, mem' for 5.0 and newer machine types

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 16 Jan 2020 11:42:09 +0100
Michal Privoznik <mprivozn@redhat.com> wrote:

> On 1/15/20 5:52 PM, Igor Mammedov wrote:
> > On Wed, 15 Jan 2020 16:34:53 +0100
> > Peter Krempa <pkrempa@redhat.com> wrote:
> >   
> >> On Wed, Jan 15, 2020 at 16:07:37 +0100, Igor Mammedov wrote:  
> >>> Deprecation period is ran out and it's a time to flip the switch
> >>> introduced by cd5ff8333a.
> >>> Disable legacy option for new machine types and amend documentation.
> >>>
> >>> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> >>> ---
> >>> CC: peter.maydell@linaro.org
> >>> CC: ehabkost@redhat.com
> >>> CC: marcel.apfelbaum@gmail.com
> >>> CC: mst@redhat.com
> >>> CC: pbonzini@redhat.com
> >>> CC: rth@twiddle.net
> >>> CC: david@gibson.dropbear.id.au
> >>> CC: libvir-list@redhat.com
> >>> CC: qemu-arm@nongnu.org
> >>> CC: qemu-ppc@nongnu.org
> >>> ---
> >>>   hw/arm/virt.c        |  2 +-
> >>>   hw/core/numa.c       |  6 ++++++
> >>>   hw/i386/pc.c         |  1 -
> >>>   hw/i386/pc_piix.c    |  1 +
> >>>   hw/i386/pc_q35.c     |  1 +
> >>>   hw/ppc/spapr.c       |  2 +-
> >>>   qemu-deprecated.texi | 16 ----------------
> >>>   qemu-options.hx      |  8 ++++----
> >>>   8 files changed, 14 insertions(+), 23 deletions(-)  
> >>
> >> I'm afraid nobody bothered to fix it yet:
> >>
> >> https://bugzilla.redhat.com/show_bug.cgi?id=1783355  
> > 
> > It's time to start working on it :)
> > (looks like just deprecating stuff isn't sufficient motivation,
> > maybe actual switch flipping would work out better)
> >   
> 
> So how was the upgrade from older to newer version resolved? I mean, if 
> the old qemu used -numa node,mem=XXX and it is migrated to a host with 
> newer qemu, the cmd line can't be switched to -numa node,memdev=node0, 
> can it? I'm asking because I've just started working on this.

see commit cd5ff8333a3c87 for detailed info.
Short answer is it's not really resolved [*],
-numa node,mem will keep working on newer QEMU but only for old machine types
new machine types will accept only -numa node,memdev.

One can check if "mem=' is supported by using QAPI query-machines
and checking numa-mem-supported field. That field is flipped to false
for 5.0 and later machine types in this patch.


*) I might give another try to removing 'mem' completely in migration
compatible manner but that's well beyond the scope of this series
So far I hasn't been able to convince myself that previous attempts
to do it were absolutely correct for all corner cases that are there.

> Michal