Re: slow guest performance with build load, looking for ideas

[Mark McLoughlin <markmc@redhat.com>]

On Thu, 2009-07-02 at 12:41 +0300, Avi Kivity wrote:
> On 07/02/2009 08:48 AM, Avi Kivity wrote:
> >> HOST time (make -j12&&   make -j12 modules) with no guest running
> >> ----------------------------------------------------------------
> >> real    6m50.936s
> >> user    29m12.051s
> >> sys    5m50.867s
> >>
> >
> > 35 minutes cpu run on 7 minutes real time, so scaling 1:7.  User time 
> > almost the same, system time different but not enough to account for 
> > the large difference in run time.
> >
> > I'm due to get my own Nehalem next week, I'll try to reproduce your 
> > results here.
> >
> 
> I reproduced this on a 2x4 barcelona, I get 6.6x scaling on the guest 
> compared to your 7.2x on the host.  This is with a kvm.git host kernel.  
> Once thing that changed is an improvement in cfq with multiple threads; 
> try setting the host io scheduler for /dev/sdb to deadline (together 
> with dropping -usbdevice tablet).

Haven't followed the thread in great detail, but has anyone tried
putting the virtio disk back into rotational mode?

See also:

  https://bugzilla.redhat.com/509383

and:

  http://lkml.org/lkml/2008/10/27/84

Cheers,
Mark.