fluxcoil wiki

generic hints

Keep load on all dom0 and domU as low as possible, disable services etc.
dom0-memory should be 256MB-512MB at least. Pinning it in grub.conf on boottime with parameters like “dom0_mem=” is preferred over letting the memory ballon by linux, already caused problems.
Try to avoid 'file:'-definitions in the config of the domU, use 'tap:io' (the blktap-driver) or 'phy' in favor. file uses loopback-mounting and results in more layers on the way down to the real storage.
Experiment with different xen-schedulers.
When using HyperThreading try using just one thread per cpu-core for pinning with domUs.
cpu-pinning:
- Try to dedicate a cpu-core or better a complete cpu to the dom0 (set (dom0-cpus 0) in /etc/xen/xend-config.sxp)
- dedicate cores to the domUs. Its better to have domUs/dom0s always use the same cores than having it jumping among cores. Dedicating cpu-cores on one cpu-socket/cpu-packages should be preferred for a dom as they are likely to communicate with each other and this happens faster inside of a cpu-socket.

usb: speedup via PVUSB (paravirtualized usb driver) possible
power management: xen nowadays can put cpus into C-states for powersaving. This is implemented in the xen-kernel, works best on newest cpus (amd younger than K10) and is not as great as the linux-implementation. One of the causes to look into using KVM instead ;)

Scheduler-tuning. Schedulers order i/o to be in the best order to be written to disc. Should be disabled in domUs (this is done in setting scheduler to 'boop') and only be active in dom0: thats the scheduler having the best overview on what has to be written/read by all domUs, and can consider all this for optimization. Such optimizations from the domUs should be disabled. Scheduling is configured through /sys/block/<disc>/queue/scheduler .

Do you really need HVM or can you run your domU para? Thats much faster!
Try to use paravirtualized drivers. For linux those can be compiled, there are even para-drivers for kernel 2.4.
there is the option to use stub-domains, offloding i/o works from your dom0

Novell is offering para-drivers since suse sles10sp1, AFAIK these are closed source and commercial
Xen/xensource is also offering non-opensourced driver for windows
windows 7/2008r2 as guest: setting viridian='1' in the domU configfile can help you utilize functions microsoft has build in for better adaption the their own hypervisor called Viridian.