Terrible performance of XenServer 6.2 and FreeBSD 10.0-RELEASE guest

[Roger Pau Monné]

On 29/03/14 14:30, Big Lebowski wrote:
> This was enabled, but I've now disabled it. However, the network I/O seems
> to be ok, on par with what I can achieve on Linux boxes. Its disk I/O that
> makes the system unusable.

I've done a `tar -Jxf src.txz` on identical boxes (which I think should
generate a similar IO workload to what you are doing), one running
FreeBSD natively, and the other running a FreeBSD PVHVM guest on top of Xen:

Native:
# time tar -Jxf src.txz

real	2m15.280s
user	0m10.021s
sys	0m5.257s

Xen guest:
# time tar -Jxf src.txz

real	3m13.366s
user	0m11.430s
sys	0m4.767s

Which doesn't look that bad. When running under Xen I didn't experience
any kind of noticeable slowness while running this workload on screen
and switched to another console.

If you think disk IO is the culprit, could you provide some synthetic
workload with fio that can reproduce this? (Also the dmesg of the
FreeBSD guest might be of interest)

My test was done using OSS Xen 4.5 and a Linux Dom0 running kernel 3.13.

Roger.