Commit-ID: 0ba87bb27d66b78e278167ac7e20c66520b8a612
Gitweb: http://git.kernel.org/tip/0ba87bb27d66b78e278167ac7e20c66520b8a612
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Wed, 1 Mar 2017 10:51:47 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Thu, 2 Mar 2017 08:50:17 +0100
sched/core: Fix pick_next_task() for RT,DL
Pavan noticed that the following commit:
49ee576809d8 ("sched/core: Optimize pick_next_task() for idle_sched_class")
... broke RT,DL balancing by robbing them of the opportinty to do new-'idle'
balancing when their last runnable task (on that runqueue) goes away.
Reported-by: Pavan Kondeti <pkondeti@xxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
Fixes: 49ee576809d8 ("sched/core: Optimize pick_next_task() for idle_sched_class")
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/core.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bbfb917..6699d43a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3273,10 +3273,15 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
struct task_struct *p;
/*
- * Optimization: we know that if all tasks are in
- * the fair class we can call that function directly:
+ * Optimization: we know that if all tasks are in the fair class we can
+ * call that function directly, but only if the @prev task wasn't of a
+ * higher scheduling class, because otherwise those loose the
+ * opportunity to pull in more work from other CPUs.
*/
- if (likely(rq->nr_running == rq->cfs.h_nr_running)) {
+ if (likely((prev->sched_class == &idle_sched_class ||
+ prev->sched_class == &fair_sched_class) &&
+ rq->nr_running == rq->cfs.h_nr_running)) {
+
p = fair_sched_class.pick_next_task(rq, prev, rf);
if (unlikely(p == RETRY_TASK))
goto again;
--
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