From 0ba87bb27d66b78e278167ac7e20c66520b8a612 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 1 Mar 2017 10:51:47 +0100 Subject: 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 Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Fixes: 49ee576809d8 ("sched/core: Optimize pick_next_task() for idle_sched_class") Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) (limited to 'kernel') diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bbfb917a9b499..6699d43a88430 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; -- cgit v1.2.3