Re: [libvirt] Qemu/KVM is 3x slower under libvirt

On Wed, Sep 28, 2011 at 11:19:43AM +0200, Reeted wrote: > On 09/28/11 09:51, Daniel P. Berrange wrote: >>> This is my bash commandline: >>> >>> /opt/qemu-kvm-0.14.1/bin/qemu-system-x86_64 -M pc-0.14 -enable-kvm >>> -m 2002 -smp 2,sockets=2,cores=1,threads=1 -name vmname1-1 -uuid >>> ee75e28a-3bf3-78d9-3cba-65aa63973380 -nodefconfig -nodefaults >>> -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/vmname1-1.monitor,server,nowait >>> -mon chardev=charmonitor,id=monitor,mode=readline -rtc base=utc >>> -boot order=dc,menu=on -drive file=/dev/mapper/vgPtpVM-lvVM_Vmname1_d1,if=none,id=drive-virtio-disk0,boot=on,format=raw,cache=none,aio=native >>> -device virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 >>> -drive if=none,media=cdrom,id=drive-ide0-1-0,readonly=on,format=raw,cache=none,aio=native >>> -device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 >>> -net nic,model=virtio -net tap,ifname=tap0,script=no,downscript=no >>> -usb -vnc 127.0.0.1:0 -vga cirrus -device >>> virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5 >> This shows KVM is being requested, but we should validate that KVM is >> definitely being activated when under libvirt. You can test this by >> doing: >> >> virsh qemu-monitor-command vmname1 'info kvm' > kvm support: enabled > > I think I would see a higher impact if it was KVM not enabled. > >>> Which was taken from libvirt's command line. The only modifications >>> I did to the original libvirt commandline (seen with ps aux) were: >>> - Network was: -netdev tap,fd=17,id=hostnet0,vhost=on,vhostfd=18 >>> -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:05:36:60,bus=pci.0,addr=0x3 >>> Has been simplified to: -net nic,model=virtio -net >>> tap,ifname=tap0,script=no,downscript=no >>> and manual bridging of the tap0 interface. >> You could have equivalently used >> >> -netdev tap,ifname=tap0,script=no,downscript=no,id=hostnet0,vhost=on >> -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:05:36:60,bus=pci.0,addr=0x3 > It's this! It's this!! (thanks for the line) > > It raises boot time by 10-13 seconds Ok, that is truely bizarre and I don't really have any explanation for why that is. I guess you could try 'vhost=off' too and see if that makes the difference.