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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) <rostedt@goodmis.org> Tested-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20170119174408.GN6485@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
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1 changed files with 2 additions and 3 deletions
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@ -3321,15 +3321,14 @@ static inline void schedule_debug(struct task_struct *prev)
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static inline struct task_struct *
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pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
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{
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const struct sched_class *class = &fair_sched_class;
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const struct sched_class *class;
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struct task_struct *p;
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/*
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* Optimization: we know that if all tasks are in
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* the fair class we can call that function directly:
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*/
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if (likely(prev->sched_class == class &&
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rq->nr_running == rq->cfs.h_nr_running)) {
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if (likely(rq->nr_running == rq->cfs.h_nr_running)) {
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p = fair_sched_class.pick_next_task(rq, prev, rf);
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if (unlikely(p == RETRY_TASK))
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goto again;
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