Some experimental results of the tests I ran on my box with the latest version of my cgroup-io-throttle patchset against the -mm kernel (2.6.27-rc5-mm1).
The goal of this test is to demonstrate the effectiveness of applying a throttling controller to enhance the IO performance predictability in a shared system.
The graphic highlights the bursty behaviour of the IO rate that we have with a plain CFQ IO scheduling (red line), and the smoother and contained behaviour using cgroup-io-throttle. We can also see the differences between the leaky bucket (green line) and token bucket (blue line) policies: first one is even more smooth and gives a better guarantee to respect the IO limit (hard limit), the second one allows a small irregularity degree (soft limit), but is better in terms of efficiency, expecially at high IO rates.
See my previous post to have an overview of the advantages this controler could provide.