Commit 74ab8e4f authored Dec 29, 2008 by Gregory Haskins

sched: use highest_prio.next to optimize pull operations



We currently take the rq->lock for every cpu in an overload state during
pull_rt_tasks().  However, we now have enough information via the
highest_prio.[curr|next] fields to determine if there is any tasks of
interest to warrant the overhead of the rq->lock, before we actually take
it.  So we use this information to reduce lock contention during the
pull for the case where the source-rq doesnt have tasks that preempt
the current task.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>

parent a8728944

kernel/sched_rt.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -1218,6 +1218,18 @@ static int pull_rt_task(struct rq *this_rq)
		continue;

		src_rq = cpu_rq(cpu);

		/*
		* Don't bother taking the src_rq->lock if the next highest
		* task is known to be lower-priority than our current task.
		* This may look racy, but if this value is about to go
		* logically higher, the src_rq will push this task away.
		* And if its going logically lower, we do not care
		*/
		if (src_rq->rt.highest_prio.next >=
		this_rq->rt.highest_prio.curr)
		continue;

		/*
		* We can potentially drop this_rq's lock in
		* double_lock_balance, and another CPU could