I have been working with Xen over the last week or so and I can't figure out why the performance is downgraded so much when booting into Xen. There are certain things that seem just as fast but other things just don't seem normal.
I have tried this on two different quad-core systems, one new generation (York) with CentOS5 and one old (Kent) with Debian Lenny but neither seem to produce good speeds.
For example, when I use the default kernels I can usually get about ~600 score out of unixbench-wht and things such as top and core systems show up as 0% cpu when running top.
When I boot into Xen kernel however, whether it been from Dom0 or the guest OS, top uses about 3% CPU and unixbench-wht produces scores under 250.
I have set vcpus to 4 and have even tried vcpu-pin 0 0, 1 1, 2 2, 3 3 but nothing seems to be changing anything. The disk speeds seem about the same (hdparm). I'm assuming it is something with the CPU, any ideas?