Re: performance trouble

[Vadim Rozenfeld <vrozenfe@redhat.com>]

On Thursday, March 22, 2012 10:52:42 AM Peter Lieven wrote:
> On 22.03.2012 09:48, Vadim Rozenfeld wrote:
> > On Thursday, March 22, 2012 09:53:45 AM Gleb Natapov wrote:
> >> On Wed, Mar 21, 2012 at 06:31:02PM +0100, Peter Lieven wrote:
> >>> On 21.03.2012 12:10, David Cure wrote:
> >>>> 		hello,
> >>>> 
> >>>> Le Tue, Mar 20, 2012 at 02:38:22PM +0200, Gleb Natapov ecrivait :
> >>>>> Try to add<feature policy='disable' name='hypervisor'/>   to cpu
> >>>>> definition in XML and check command line.
> >>>>> 
> >>>> 	ok I try this but I can't use<cpu model>   to map the host cpu
> >>>> 
> >>>> (my libvirt is 0.9.8) so I use :
> >>>>    <cpu match='exact'>
> >>>>    
> >>>>      <model>Opteron_G3</model>
> >>>>      <feature policy='disable' name='hypervisor'/>
> >>>>    
> >>>>    </cpu>
> >>>> 	
> >>>> 	(the physical server use Opteron CPU).
> >>>> 
> >>>> 	The log is here :
> >>>> http://www.roullier.net/Report/report-3.2-vhost-net-1vcpu-cpu.txt.gz
> >>>> 
> >>>> 	And now with only 1 vcpu, the response time is 8.5s, great
> >>>> 
> >>>> improvment. We keep this configuration for production : we check the
> >>>> response time when some other users are connected.
> >>> 
> >>> please keep in mind, that setting -hypervisor, disabling hpet and
> >>> only one vcpu
> >>> makes windows use tsc as clocksource. you have to make sure, that your
> >>> vm is not switching between physical sockets on your system and that
> >>> you have constant_tsc feature to have a stable tsc between the cores
> >>> in the same socket. its also likely that the vm will crash when live
> >>> migrated.
> >> 
> >> All true. I asked to try -hypervisor only to verify where we loose
> >> performance. Since you get good result with it frequent access to PM
> >> timer is probably the reason. I do not recommend using -hypervisor for
> >> production!
> >> 
> >>> @gleb: do you know whats the state of in-kernel hyper-v timers?
> >> 
> >> Vadim is working on it. I'll let him answer.
> > 
> > It would be nice to have synthetic timers supported. But,  at the moment,
> > I'm only researching  this feature.
> 
> So it will take months at least?

I would say weeks.

> 
> What do the others think, would it be feasible to make a proper in-kernel
> pmtimer solution in the meantime.
> 
> I think Windows guest performance is very important for the success of KVM.
> 
> Peter
> 
> >>> peter
> >>> 
> >>>> 	David.
> >>>> 
> >>>> --
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> >> 
> >> --
> >> 
> >> 			Gleb.