Poor write- and overall performance

[Arne Kepp <ak@opengeo.org>]

Hi,

I'm testing KVM 80 (prepackaged from lfarkas.org) on CentOS 5.2 (both 
guest and host) and comparing against Xen 3.3.0. The only modification 
I've really made is that I've set noatime on both guest and host. The 
guest is running straight from an LVM volume and is assigned 4 Gb RAM 
and 4 virtual CPUs.

KVM does well reading from disk (300 Mbyte/s according to IOZone, 
virtually the same as native) and computational tasks like OpenSSL 
signing.  But writing ends up at 30 Mbyte/s (native does 150 Mbyte/s) 
and kernel compilation times are roughly double that of native. KVM 79 
exhibited the same behavior for disk IO, but froze while compiling the 
kernel.

So, short of using the virtio drivers (which I think would require a 
custom kernel since RHEL 5.2 uses 2.6.18), are there any easy tweaks I 
should try to make KVM fare better ?

The host is quad core Intel with 8 Gb RAM and a SAS RAID 5 
configuration. Let me know if you'd like to see the results here.

Sincerely,
-Arne

-- 
Arne Kepp
OpenGeo - http://opengeo.org
Expert service straight from the developers