[Qemu-devel] Re: [PATCH] qemu-kvm: introduce cpu_start/cpu_stop commands

[Anthony Liguori]

On 11/22/2010 05:56 PM, Chris Wright wrote:
> * Anthony Liguori (address@hidden) wrote:
>    
> > On 11/22/2010 05:04 PM, Chris Wright wrote:
> >      
> > > * Anthony Liguori (address@hidden) wrote:
> > >        
> > > > qemu-kvm vcpu threads don't response to SIGSTOP/SIGCONT.  Instead of teaching
> > > > them to respond to these signals, introduce monitor commands that stop and start
> > > > individual vcpus.
> > > >          
> > > In the past SIGSTOP has introduced time skew.  Have you verified this
> > > isn't an issue.
> > >        
> > Time skew is a big topic.  Are you talking about TSC drift,
> > pit/rtc/hpet drift, etc?
> >      
> Sorry to be vague, but it's been long enough that I don't recall
> the details.  The guest kernel's clocksource effected how timekeeping
> progressed across STOP/CONT (was probably missing qemu based timer ticks).
> While this is not the same, made me wonder if you'd tested against that.
>    

Yeah, it's definitely going to increase the likelihood of interrupt 
coalescing but only as much as a contended CPU would already.

QEMU will keep getting timer ticks but the guest won't process them in a 
timely fashion.

> > It's certainly going to stress periodic interrupt catch up code.
> >      
> Heh, call it a feature for autotest ;)
>    

Excellent idea :-)

Regards,

Anthony Liguori

> thanks,
> -chris
>