CPU Load Balancer / Scheduler / CFS

[Robert W]

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.

What could be going on here?
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