Re: performance trouble

[Gleb Natapov <gleb@redhat.com>]

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.

> peter
> 
> >	David.
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--
			Gleb.