sys_sched_yield fast path

[Mike Kravetz <mkravetz@sequent.com>]

Any thoughts about adding a 'fast path' to the SMP code in
sys_sched_yield.  Why not compare nr_pending to smp_num_cpus
before examining the aligned_data structures?  Something like,

if (nr_pending > smp_num_cpus)
	goto set_resched_now;

Where set_resched_now is a label placed just before the code
that sets the need_resched field of the current process.
This would eliminate touching all the aligned_data cache lines
in the case where nr_pending can never be decremented to zero.

Also, would it make sense to stop decrementing nr_pending to
prevent it from going negative?  OR  Is the reasoning that in
these cases there is so much 'scheduling' activity that we
should force the reschedule?

-- 
Mike Kravetz                                 mkravetz@sequent.com
IBM Linux Technology Center