On Tue, 2007-07-31 at 13:48 +0200, Sébastien Dugué wrote:

On Mon, 30 Jul 2007 14:50:34 -0700 Josh Triplett [off-list ref] wrote:

quoted

On Tue, 2007-07-24 at 15:42 +0200, Sébastien Dugué wrote:

quoted

  this one-liner fixes a bug in balance_rt_tasks() which sometimes manifests by
having a lower prio task being scheduled while a higher prio task is sitting
waiting on another runqueue.

  This is pretty hard to reproduce on low cpu count machines, for example, I
had to have sched_football run in a loop for ~38h before it failed on a dual HT
Xeon box.

Very impressive find, and this does seem to improve things in some
cases.

However, with 2.6.22.1-rt8, which includes this patch, I still managed
to get some failures after a few hours on an 8-way (quad dual-core) box.
Preliminary results so far:
    420 Final ball position: 0
      2 Final ball position: 1

  Darn, I thought it was it :(

  I had a ~60h run on my box with the very same kernel without a single
failure.

I think you really need a box with more processors to reproduce these
problems in a reasonable timeframe.  Happy to test any patches you have
to fix RT balancing; please let me know.

  Do you have any other user RT load running when those failures pop up?

Other than sched_football, I had sshd, bash, and GNU screen,
theoretically all 100% idle (no input to read and no output to display).

- Josh Triplett