I've followed instructions on http://www.linux-kvm.org/page/Tuning_KVM. Host is Debian Squeeze Kernel 3.2, QEMU 1.0, libvirt 0.9.12 (all from squeeze-backport). All 4 guests are Debian Squeeze Kernel 3.2, also.
So my settings in Guest XML are
<cpu model='host-passthrough'/> <disk [...]/> <driver name='qemu' type='raw' cache='none'/> <target [...] bus='virtio'/> </disk> <interface [...]> <model type='virtio'/> </interface>
IO scheduler on guests is set to noop. On host I tried noop/deadline/cfq with no significant performance differences, for me. All guests storage is provided by LVM. When using
cache='none' and all guests have no noteworthy load, the 15 minutes average CPU load on host goes up to 3-4. But when using
cache='writeback' the hosts CPU loaded rises down to less than 1. Can anyone explain, why the suggested settings for LVM causes the higher load on host?
BTW: When running disk benchmarks, the option
none results in higher IO performance than