Re: performance trouble

[Gleb Natapov <gleb@redhat.com>]

On Tue, Mar 27, 2012 at 02:28:04PM +0200, Peter Lieven wrote:
> On 27.03.2012 14:26, Gleb Natapov wrote:
> >On Tue, Mar 27, 2012 at 02:20:23PM +0200, Peter Lieven wrote:
> >>On 27.03.2012 12:00, Gleb Natapov wrote:
> >>>On Tue, Mar 27, 2012 at 11:26:29AM +0200, 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?
> >>>>
> >>>>the stuff you send yesterday is for qemu, right? would
> >>>>it be possible to use it in qemu-kvm also?
> >>>>
> >>>No, they are for kernel.
> >>i meant the qemu.diff file.
> >>
> >Yes, I missed the second attachment.
> >
> >>if i understand correctly i have to pass -cpu host,+hv_refcnt to qemu?
> >>
> >Looks like it.
> ok, so it would be interesting if it helps to avoid the pmtimer reads
> we observed earlier. right?
> 
Yes.

--
			Gleb.