In recent O(1) scheduler releases, an optimization was made that removed
schedule_tail from UP kernels. This causes the initial preempt_count of
a new task, which starts at 1, to never decrement to zero and thus never
become preemptible. CONFIG_PREEMPT requires schedule_tail, too.
Users of 2.4+O(1)+preempt (i.e. -ac) should use this patch:
instead. Thanks to everyone who pointed out the lousy performance. Enjoy,
Robert Love
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