Re: performance trouble

[Vadim Rozenfeld <vrozenfe@redhat.com>]

On Tuesday, March 27, 2012 10:56:05 AM Gleb Natapov wrote:
> On Mon, Mar 26, 2012 at 10:11:43PM +0200, Vadim Rozenfeld wrote:
> > 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-cp
> > > >>>>>>>>>> u.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%28
> > > >> v=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.
> 
> To clarify the thing that microsoft qpc uses is what is implemented by
> the patch Vadim attached to his previous email. But I believe that
> additional qemu patch is needed for Windows to actually use it.

You are right.
bits 1 and 9 must be set to on in leaf 0x40000003 and HPET
should be completely removed from ACPI. 
> 
> --
> 			Gleb.