sched: Rework pick_next_task() slow-path
Avoid the RETRY_TASK case in the pick_next_task() slow path. By doing the put_prev_task() early, we get the rt/deadline pull done, and by testing rq->nr_running we know if we need newidle_balance(). This then gives a stable state to pick a task from. Since the fast-path is fair only; it means the other classes will always have pick_next_task(.prev=NULL, .rf=NULL) and we can simplify. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Aaron Lu <aaron.lwe@gmail.com> Cc: Valentin Schneider <valentin.schneider@arm.com> Cc: mingo@kernel.org Cc: Phil Auld <pauld@redhat.com> Cc: Julien Desfossez <jdesfossez@digitalocean.com> Cc: Nishanth Aravamudan <naravamudan@digitalocean.com> Link: https://lkml.kernel.org/r/aa34d24b36547139248f32a30138791ac6c02bd6.1559129225.git.vpillai@digitalocean.com
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