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

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

But now I don't know where to look.... During boot there is a pause usually between /scripts/init-bottom (Ubuntu 11.04 guest) and the appearance of login prompt, however that is not really meaningful because there is probably much background activity going on there, with init etc. which don't display messages init-bottom does just this --------------------------------- #!/bin/sh -e # initramfs init-bottom script for udev PREREQ="" # Output pre-requisites prereqs() { echo "$PREREQ" } case "$1" in prereqs) prereqs exit 0 ;; esac # Stop udevd, we'll miss a few events while we run init, but we catch up pkill udevd # Move /dev to the real filesystem mount -n -o move /dev ${rootmnt}/dev --------------------------------- It doesn't look like it should take time to execute. So there is probably some other background activity going on... and that is slower, but I don't know what that is. Another thing that can be noticed is that the dmesg message: [ 13.290173] eth0: no IPv6 routers present (which is also the last message) happens on average 1 (one) second earlier in the fast case (-net) than in the slow case (-netdev)