Re: [Qemu-devel] KVM brokenness due to IO thread changes

[Anthony Liguori]

Jan Kiszka wrote:
> Marcelo Tosatti wrote:
>   
> > Jan,
> >
> > On Tue, Apr 28, 2009 at 09:40:01AM +0200, Jan Kiszka wrote:
> >     
> > > Hi,
> > >
> > > this is a heads-up, maybe someone has some time to look into this over
> > > the day: I seems like the IO thread changes caused a few regressions to
> > > the KVM mode.
> > >
> > > When I keep this feature disabled, I see strange hick-ups of the event
> > > delivery mechanism, and the guest stops once in a while for a second or
> > > so. Attaching strace makes the whole process terminate early (looks like
> > > it triggers a race in the signal handling). And when I enable the IO
> > > thread, I immediately get a deadlock on qemu_global_mutex.
> > >       
> > Yes its borked. The iothread should signal the vcpu thread whenever it
> > wants to grab the mutex lock, because unlike kvm-userspace it does not
> > drop the global mutex when entering guest mode (VCPU_RUN ioctl).
> >
> > Anthony will commit patches to fix that soon.
> >     
>
> Looking forward. It's far more efficient to test my infrastructure
> changes against the KVM mode.
>   

N.B. he's seeing issues with the IO thread disabled.

I've not seen this myself and my patch doesn't fix that problem.

Regards,

Anthony Liguori