I'm seeing some bizarre differences between two servers (one running 2.6.32 and the other 2.6.18) with how processes are spread across CPUs. I created a simple test client: https://gist.github.com/2306761 which forks 4 times to create processes which just consume cpu. On 2.6.18, the processes are distributed across CPUs as expected (all 4 processes are consuming 100%). But on 2.6.32, the distribution varies. Sometimes it's (100%, 33%, 33%, 33%), other times it's (100%, 100%, 50%, 50%), etc.. while all the other CPUs sit completely idle.. Both servers have many cores (more than 4). Both servers each have 2 physical processors, and are hyper-threaded. I've done many other similar tests (tried running the "stress" program with different parameters and I also got bizarre results. It basically looks like the CPU Load Balancer never moves a process to a different CPU under any circumstances). I haven't set anything regarding cpusets / etc. so it should all be default behavior. Also, if I manually move the processes to other cpus (using taskset) then I can get them to all run at 100%. What could be going on here?