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Re: [libvirt] [RFC 12/42] pc: initialize legacy hotplug only for 2.6 and older machine types



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 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.

Peter

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