From mboxrd@z Thu Jan  1 00:00:00 1970
From: Vadim Rozenfeld <vrozenfe@redhat.com>
Subject: Re: performance trouble
Date: Thu, 22 Mar 2012 10:48:58 +0200
Message-ID: <201203221048.59643.vrozenfe@redhat.com>
References: <20120222163356.GE26955@nfs-rbx.ovh.net> <4F6A1056.1020904@dlh.net> <20120322075345.GA22368@redhat.com>
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Cc: Peter Lieven <pl@dlh.net>, David Cure <kvm@cure.nom.fr>,
	Avi Kivity <avi@redhat.com>, kvm@vger.kernel.org
To: Gleb Natapov <gleb@redhat.com>
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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.
> 
> > peter
> > 
> > >	David.
> > >
> > >--
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> 
> --
> 			Gleb.