vCPU scalability for linux VMs

[Alec Istomin <alec@openvz.org>]

Gentlemen,
 Reaching out with a non-development question, sorry if it's not
 appropriate here.
 
 I'm looking for a way to improve Linux SMP VMs performance under KVM.

 My preliminary results show that single vCPU Linux VMs perform up to 10
 times better than 4vCPU Linux VMs (consolidated performance of 8 VMs on
 8 core pre-Nehalem server). I suspect that I'm missing something major
 and look for any means that can help improve SMP VMs performance.


VMs are started using:
qemu-kvm -m $ram -smp $cpus -name $name -drive file=${newimg},boot=on,cache=writethrough  -net nic,macaddr=$mac,vlan=0,model=virtio -net tap,script=/kvm/qemu-ifup,vlan=0,ifname=kvmnet$i -parallel none -usb -k en-us  -monitor pty -serial pty -nographic -daemonize -snapshot


KVM Host Environment (redhat 5 based):
# uname -r
2.6.18-194.el5
# rpm -qa|grep kvm
kvm-83-164.el5
kvm-tools-83-164.el5
kmod-kvm-83-164.el5
kvm-qemu-img-83-164.el5



Thank you,
 Alec