Reading about some users running Redis in a VM, it brought to my mind the recommendations from Redis team :
Redis runs slower on a VM. Virtualization toll is quite high because for many common operations. (...) Prefer to run Redis on a physical box, especially if you favor deterministic latencies. On a state-of-the-art hypervisor (VMWare), result of redis-benchmark on a VM through the physical network is almost divided by 2 compared to the physical machine, with some significant CPU time spent in system and interruptions.