kvm very slow

Ulrich Schreiner
2007-08-01T05:22:49Z

hi,

im using a 64 bit fedora7 system with a quad-core processor to host
multiple virtual machines.

my current kernel is:

Linux testserver 2.6.22.1-27.fc7 #1 SMP Tue Jul 17 17:19:58 EDT 2007
x86_64 x86_64 x86_64 GNU/Linux

(now there is a 2.6.22.1-33.fc7 to download, but i think it is not the
point here).

i installed

kvm.x86_64: 31-1.fc8

because of a crash i reported as a bug with the older kvm module.

this system starts a F7 image with the following command:

/usr/bin/qemu-kvm
-net nic,macadr=52.54.00.12.34.57
-net tap,script=./ifup.py,ifname=tap0
-hda /var/qemu/vm_images/F7image.img
-boot c: -m 512 -vnc :2 -k de

inside the image there is fedora 7, but a 32bit system.

almost everything works (reboot hangs), but the system is extremely
slow! the clock inside the system is extremely slow: every *virtual*
second in the image is about two or more seconds in the *real* world.

the "clocksource=pit" argument does not help.

but it is not only the clock ... the whole system is really slow!

on the other side i have an notebook with an old core2 processor which
cannot run KVM, so i run qemu/kqemu. if i start the image on this host,
i have much better performance. inside the image there is an apache,
subversion and a trac; all three systems are really fast on the notebook
compared to the quadcore 64bit host!

when starting qemu without kqemu i get a warning on console an poor
performance. when starting "qemu-kvm" i get no warning, but the same
poor performance. how can i check if the kvm-modules are really loaded?

any other ideas what i can do?

thanks