From: Peter Zijlstra Date: Thu, 19 Jan 2017 17:44:08 +0000 (+0100) Subject: sched/core: Optimize pick_next_task() for idle_sched_class X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=49ee576809d8;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git sched/core: Optimize pick_next_task() for idle_sched_class Steve noticed that when we switch from IDLE to SCHED_OTHER we fail to take the shortcut, even though all runnable tasks are of the fair class, because prev->sched_class != &fair_sched_class. Since I reworked the put_prev_task() stuff, we don't really care about prev->class here, so removing that condition will allow this case. This increases the likely case from 78% to 98% correct for Steve's workload. Reported-by: Steven Rostedt (VMware) Tested-by: Steven Rostedt (VMware) Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170119174408.GN6485@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 49ce1cb3d320..51ca21ef7ae5 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3321,15 +3321,14 @@ static inline void schedule_debug(struct task_struct *prev) static inline struct task_struct * pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) { - const struct sched_class *class = &fair_sched_class; + const struct sched_class *class; struct task_struct *p; /* * Optimization: we know that if all tasks are in * the fair class we can call that function directly: */ - if (likely(prev->sched_class == class && - rq->nr_running == rq->cfs.h_nr_running)) { + if (likely(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;