Re: [RFC] kvm: x86: export vCPU halted state to sysfs

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 2 Feb 2018 16:49:54 -0500
Luiz Capitulino <lcapitulino@redhat.com> wrote:

> On Fri, 2 Feb 2018 18:41:44 -0200
> Eduardo Habkost <ehabkost@redhat.com> wrote:
> 
> > On Fri, Feb 02, 2018 at 03:19:45PM -0500, Luiz Capitulino wrote:  
> > > On Fri, 2 Feb 2018 18:09:12 -0200
> > > Eduardo Habkost <ehabkost@redhat.com> wrote:    
> > [...]  
> > > > Your plan above covers what will happen when using newer QEMU
> > > > versions, but libvirt still needs to work sanely if running QEMU
> > > > 2.11.  My suggestion is that libvirt do not run query-cpus to ask
> > > > for the "halted" field on any architecture except s390.    
> > > 
> > > My current plan is to ask libvirt to completely remove query-cpus
> > > usage, independent of the arch and use the new command instead.    
> > 
> > This would be a regression for people running QEMU 2.11 on s390.  
> 
> libvirt could use query-cpus on s390 if the new command is not
> available.

Btw, even on s390 query-cpus runs run_on_cpu(), which is what
causes vCPUs to go to user-space. So, s390 should suffer the same
performance problem. Pick your regression.

> 
> > 
> > (But maybe it would be an acceptable regression?  Viktor, what do
> > you think?  Are there production releases of management systems
> > that already rely on vcpu.<n>.halted?)
> >   
>