Re: performance trouble

[Vadim Rozenfeld <vrozenfe@redhat.com>]

On Monday, March 26, 2012 08:54:50 PM Peter Lieven wrote:
> On 26.03.2012 20:36, Vadim Rozenfeld wrote:
> > On Monday, March 26, 2012 07:52:49 PM Gleb Natapov wrote:
> >> On Mon, Mar 26, 2012 at 07:46:03PM +0200, Vadim Rozenfeld wrote:
> >>> On Monday, March 26, 2012 07:00:32 PM Peter Lieven wrote:
> >>>> On 22.03.2012 10:38, Vadim Rozenfeld wrote:
> >>>>> 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.tx
> >>>>>>>>>> t.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.
> >>>> 
> >>>> Is there a way, we could contribute and help you with this?
> >>> 
> >>> Hi Peter,
> >>> You are welcome to add  an appropriate handler.
> >> 
> >> I think Vadim refers to this HV MSR
> >> http://msdn.microsoft.com/en-us/library/windows/hardware/ff542633%28v=vs
> >> .85 %29.aspx
> > 
> > This one is pretty simple to support. Please see attachments for more
> > details. I was thinking about synthetic  timers
> > http://msdn.microsoft.com/en-
> > us/library/windows/hardware/ff542758(v=vs.85).aspx
> 
> is this what microsoft qpc uses as clocksource in hyper-v?
Yes, it should be enough for Win7 / W2K8R2.  
Cheers,
Vadim.
> i will check tomorrow.
> 
> thanks
> vadim
> 
> >> --
> >> 
> >> 			Gleb.