On Thu, 12 May 2016 15:27:04 +0200
Peter Krempa <pkrempa(a)redhat.com> wrote:
On Thu, May 12, 2016 at 15:20:51 +0200, Igor Mammedov wrote:
> On Thu, 12 May 2016 13:04:23 +0200
> Peter Krempa <pkrempa(a)redhat.com> wrote:
>
> > On Thu, May 12, 2016 at 07:52:23 -0300, Eduardo Habkost wrote:
> > > I don't think we should do that, unless users already had time to
> > > update their scripts and libvirt had time to implement code
> > > supporting the new method.
> > >
> > > I believe libvirt (and people's scripts) use maxcpus only when
> > > they want CPU hotplug, so making max_cpus > smp_cpus enable CPU
> > > hotplug implicitly would probably solve the compatibility issue.
> >
> > Libvirt uses maxcpus only if the configuration explicitly has less
> > active cpus than the maximum number. This option would be the best IMO.
> >
> > > If we want to deprecate the use of maxcpus to enable CPU hotplug,
> > > then we can make it print a warning for a few releases, so people
> > > have time to update their code.
> >
> > At that point libvirt also needs a way to detect that the new argument
> > is supported by qemu, so we can start passing it on the command line
> > basically every time we now pass 'maxcpus'.
> >
> > The warning will get most probably ignored by people using libvirt as
> > the stdout/err of qemu is not visible to them.
> Ok, to make things less complicated I'll drop machine.cpu-hotplug
> and leave it always enabled as it used to be and as Michael suggested.
>
> I'll drop following patches: 12, 13, 14, 20, 23 and respin series
I actually don't mind disabling it. But I'd be glad if it was based on
the max_cpus value as Eduardo suggested.
I've already dropped it, and
simplifies series quite a bit.
So lets continue without disabling for now.
Later we can consider disabling it if we agree on conditions when it should happen.
smp_cpus < max_cpus is not a good enough I think:
On Wed, 11 May 2016 15:50:39 +0200
Igor Mammedov <imammedo(a)redhat.com> wrote:
> On Tue, 10 May 2016 17:24:14 -0300
> Eduardo Habkost <ehabkost(a)redhat.com> wrote:
[...]
> > Should max_cpus > smp_cpus automatically set
> > cpu-hotplug=on?
> I'd prefer dumb explicit feature enablement,
> as it doesn't put any assumptions on other options and
> QEMU + mgmt don't have to maintain logic for implicit
> rules that might enable it.
>
> and if I didn't manage to push 'device_add x86cpu' in 2.7 time frame,
> guess work gets a bit confusing with current cpu-add semantic,
> consider current:
>
> SRC-QEMU -smp 1,maxcpus=2
> cpu-add 1
> DST-QEMU -smp 2,maxcpus=2
>
> vs would be device_add:
>
> SRC-QEMU -smp 1,maxcpus=2
> device_add cpu
> DST-QEMU -smp 1,maxcpus=2 -device cpu
>
> so instead of qemu/users guessing, I suggest to make it explictly
> enabled to get feature (which is mostly optional) or
> cleanly fail qemu start if confusing options are specified
> with a clear error message.