Re: [Qemu-devel] Re: [RFD] virtio: Add memory statistics reporting to the balloon driver

[Luiz Capitulino <lcapitulino@redhat.com>]

On Fri, 08 Jan 2010 11:01:31 -0600
Adam Litke <agl@us.ibm.com> wrote:

> On Thu, 2010-01-07 at 16:30 -0200, Luiz Capitulino wrote:
> > On Thu, 7 Jan 2010 15:58:30 -0200
> > Luiz Capitulino <lcapitulino@redhat.com> wrote:
> > 
> > >  I like Daniel's idea too. In practice 'refresh-balloon' is going to
> > > be Anthony's idea #1 for the QMP case, which seems the right way to
> > > do it with QMP.
> > 
> >  Hm, something that has just occurred to me: it's easy to have
> > async messages in the user Monitor, we could add a new type of
> > user print callback called async_print.
> > 
> >  This new callback would be called by the Monitor when the async
> > message API is called but we are in user mode.
> > 
> >  This is really today's user_print, but user data is printed
> > asynchronously.
> 
> There is one thing I am struggling with as I try to implement this
> asynchronous behavior.  How can I suspend the monitor thread to wait for
> the stats update to come through?  I see qemu_cond_timedwait(), but that
> appears to only be used for a VM's cpu threads.  I also see the bottom
> half infrastructure, but I am not sure if that is appropriate either. 

 IIUC, in QMP you won't wait at all and I believe suspend/resume should
work on the user Monitor.

 You can use monitor_ctrl_mode() to know whether you're in QMP or not.