path: root/kernel/sched_rt.c
diff options
authorGregory Haskins <ghaskins@novell.com>2008-01-25 21:08:10 +0100
committerIngo Molnar <mingo@elte.hu>2008-01-25 21:08:10 +0100
commit318e0893ce3f524ca045f9fd9dfd567c0a6f9446 (patch)
tree94eb9b03fc51033e87bc222861a5906233abae67 /kernel/sched_rt.c
parentsched: RT balancing: include current CPU (diff)
sched: pre-route RT tasks on wakeup
In the original patch series that Steven Rostedt and I worked on together, we both took different approaches to low-priority wakeup path. I utilized "pre-routing" (push the task away to a less important RQ before activating) approach, while Steve utilized a "post-routing" approach. The advantage of my approach is that you avoid the overhead of a wasted activate/deactivate cycle and peripherally related burdens. The advantage of Steve's method is that it neatly solves an issue preventing a "pull" optimization from being deployed. In the end, we ended up deploying Steve's idea. But it later dawned on me that we could get the best of both worlds by deploying both ideas together, albeit slightly modified. The idea is simple: Use a "light-weight" lookup for pre-routing, since we only need to approximate a good home for the task. And we also retain the post-routing push logic to clean up any inaccuracies caused by a condition of "priority mistargeting" caused by the lightweight lookup. Most of the time, the pre-routing should work and yield lower overhead. In the cases where it doesnt, the post-router will bat cleanup. Signed-off-by: Gregory Haskins <ghaskins@novell.com> Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to '')
1 files changed, 19 insertions, 0 deletions
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 95f36f61ae1d..ac7d06786454 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -151,8 +151,27 @@ yield_task_rt(struct rq *rq)
+static int find_lowest_rq(struct task_struct *task);
static int select_task_rq_rt(struct task_struct *p, int sync)
+ struct rq *rq = task_rq(p);
+ /*
+ * If the task will not preempt the RQ, try to find a better RQ
+ * before we even activate the task
+ */
+ if ((p->prio >= rq->rt.highest_prio)
+ && (p->nr_cpus_allowed > 1)) {
+ int cpu = find_lowest_rq(p);
+ return (cpu == -1) ? task_cpu(p) : cpu;
+ }
+ /*
+ * Otherwise, just let it ride on the affined RQ and the
+ * post-schedule router will push the preempted task away
+ */
return task_cpu(p);
#endif /* CONFIG_SMP */