Re: performance trouble

[Vadim Rozenfeld <vrozenfe@redhat.com>]

On Tuesday, March 27, 2012 11:26:29 AM Peter Lieven wrote:
> On 27.03.2012 11:23, Vadim Rozenfeld wrote:
> > 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.
> 
> could you advise how to do this and/or make a patch?
Gleb mentioned that it properly handled in upstream,
otherwise just comment the entire HPET section in 
acpi-dsdt.dsl file.
> 
> the stuff you send yesterday is for qemu, right? would
> it be possible to use it in qemu-kvm also?
Yes, but don't forget about kvm patch as well.
> 
> peter
> 
> >> --
> >> 
> >> 			Gleb.