On Wed, Mar 01, 2017 at 10:53:03AM -0500, Steven Rostedt wrote: > Peter, do we have a solution for this yet? Are you going to add the one > with the linker magic?
I queued the below earlier today. --- Subject: sched: Fix pick_next_task() for RT,DL From: Peter Zijlstra <[email protected]> Date: Wed Mar 1 10:51:47 CET 2017 Pavan noticed that 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. Cc: Steven Rostedt <[email protected]> Reported-by: Pavan Kondeti <[email protected]> Fixes: 49ee576809d8 ("sched/core: Optimize pick_next_task() for idle_sched_class") Signed-off-by: Peter Zijlstra (Intel) <[email protected]> --- --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3273,10 +3273,15 @@ pick_next_task(struct rq *rq, struct tas 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 @pref 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;
