linux-kernel - CPU Load Balancer / Scheduler / CFS

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Message-ID: <CADEOusebxthJy3s7oCpujXL+KHkFVGH=19psFX2T2B88BOacEQ@mail.gmail.com>
Date:	Wed, 4 Apr 2012 20:53:25 -0400
From:	Robert W <robertwalters83@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: CPU Load Balancer / Scheduler / CFS

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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