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

[Avi Kivity <avi@redhat.com>]

Erik Jacobson wrote:
> We have been trying to test qemu-kvm virtual machines under an IO load.
> The IO load is quite simple: A timed build of the linux kernel and modules.
> I have found that virtual machines take more than twice as long to do this
> build as the host.  It doesn't seem to matter if I use virtio or not,  Using
> the same device and same filesystem, the host is more than twice as fast.
>
> We're hoping that we can get some advice on how to address this issue.  If
> there are any options I should add for our testing, we'd appreciate it.  I'm
> also game to try development bits to see if they make a difference.  If it
> turns out "that is just the way it is right now", we'd like to know that
> too.
>
> For these tests, I used Fedora 11 as the virtualization server.  I did this
> because it has recent bits.  I experimented with SLES11 and Fedora11 guests.
>
> In general, I used virt-manager to do the setup and launching.  So the
> qemu-kvm command lines are based on that (and this explains why they are
> a bit long).  I then modified the qemu-kvm command line to perform other
> variations of the test.  Example command lines can be found at the end of
> this message.
>
> I performed tests on two different systems to be sure it isn't related to
> specific hardware.
>   

What is the host cpu type?  On pre-Nehalem/Barcelona processors kvm has 
poor scalability in mmu intensive workloads like kernel builds.

-- 
error compiling committee.c: too many arguments to function