Re: [Qemu-devel] Re: [PATCH 2/7] Enable I/O thread and VNC threads by default

[Anthony Liguori]

On 02/09/2011 06:35 PM, Aurelien Jarno wrote:
> On Tue, Feb 08, 2011 at 04:08:28PM +0100, Aurelien Jarno wrote:
>    
> > Aurelien Jarno a écrit :
> >      
> > > Paolo Bonzini a écrit :
> > >        
> > > > On 02/08/2011 12:15 PM, Aurelien Jarno wrote:
> > > >          
> > > > > however
> > > > > it should not be done ignoring all the*current*  drawbacks of the
> > > > > iothread mode. We know them (at least for some of them), so let's try to
> > > > > solve them.
> > > > >            
> > > > Let's also enumerate them.
> > > >
> > > >          
> > >  From what I know:
> > > - performance regression in TCG mode
> > >        
> > I setup an x86_64 guest on an x86_64 host (Intel Xeon E5345). Nothing
> > was running except the standard daemons and the CPU governor was set to
> > "performance" on all CPU. I then compared the network performance using
> > netperf in default mode, through a tap interface and a virtio nic. I got
> > the following results (quite reproducible, std below 0.5):
> > - without IO thread: 107.36 MB/s
> > - with IO thread:     89.93 MB/s
> >
> >      
> And the same test on the code from september 2009:
> - without IO thread: 141.8 MB/s
>    

virtio-net is super finicky regarding mitigation strategies and their 
relationship to the I/O thread.  Different benchmarks will behave 
differently.  virtio-blk is probably a better device to test as you'll 
get much more consistent results across different type of I/O patterns.

Regards,

Anthony Liguori