sched: Migrate sched to use new tick dependency mask model
Instead of providing asynchronous checks for the nohz subsystem to verify sched tick dependency, migrate sched to the new mask. Everytime a task is enqueued or dequeued, we evaluate the state of the tick dependency on top of the policy of the tasks in the runqueue, by order of priority: SCHED_DEADLINE: Need the tick in order to periodically check for runtime SCHED_FIFO : Don't need the tick (no round-robin) SCHED_RR : Need the tick if more than 1 task of the same priority for round robin (simplified with checking if more than one SCHED_RR task no matter what priority). SCHED_NORMAL : Need the tick if more than 1 task for round-robin. We could optimize that further with one flag per sched policy on the tick dependency mask and perform only the checks relevant to the policy concerned by an enqueue/dequeue operation. Since the checks aren't based on the current task anymore, we could get rid of the task switch hook but it's still needed for posix cpu timers. Reviewed-by: Chris Metcalf <cmetcalf@ezchip.com> Cc: Christoph Lameter <cl@linux.com> Cc: Chris Metcalf <cmetcalf@ezchip.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Luiz Capitulino <lcapitulino@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
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@ -2364,10 +2364,7 @@ static inline void wake_up_nohz_cpu(int cpu) { }
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#endif
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#ifdef CONFIG_NO_HZ_FULL
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extern bool sched_can_stop_tick(void);
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extern u64 scheduler_tick_max_deferment(void);
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#else
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static inline bool sched_can_stop_tick(void) { return false; }
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#endif
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#ifdef CONFIG_SCHED_AUTOGROUP
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@ -701,31 +701,36 @@ static inline bool got_nohz_idle_kick(void)
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#endif /* CONFIG_NO_HZ_COMMON */
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#ifdef CONFIG_NO_HZ_FULL
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bool sched_can_stop_tick(void)
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bool sched_can_stop_tick(struct rq *rq)
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{
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int fifo_nr_running;
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/* Deadline tasks, even if single, need the tick */
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if (rq->dl.dl_nr_running)
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return false;
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/*
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* FIFO realtime policy runs the highest priority task. Other runnable
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* tasks are of a lower priority. The scheduler tick does nothing.
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* FIFO realtime policy runs the highest priority task (after DEADLINE).
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* Other runnable tasks are of a lower priority. The scheduler tick
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* isn't needed.
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*/
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if (current->policy == SCHED_FIFO)
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fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
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if (fifo_nr_running)
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return true;
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/*
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* Round-robin realtime tasks time slice with other tasks at the same
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* realtime priority. Is this task the only one at this priority?
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* realtime priority.
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*/
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if (current->policy == SCHED_RR) {
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struct sched_rt_entity *rt_se = ¤t->rt;
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return list_is_singular(&rt_se->run_list);
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if (rq->rt.rr_nr_running) {
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if (rq->rt.rr_nr_running == 1)
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return true;
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else
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return false;
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}
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/*
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* More than one running task need preemption.
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* nr_running update is assumed to be visible
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* after IPI is sent from wakers.
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*/
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if (this_rq()->nr_running > 1)
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/* Normal multitasking need periodic preemption checks */
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if (rq->cfs.nr_running > 1)
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return false;
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return true;
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@ -1279,6 +1279,35 @@ unsigned long to_ratio(u64 period, u64 runtime);
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extern void init_entity_runnable_average(struct sched_entity *se);
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#ifdef CONFIG_NO_HZ_FULL
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extern bool sched_can_stop_tick(struct rq *rq);
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/*
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* Tick may be needed by tasks in the runqueue depending on their policy and
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* requirements. If tick is needed, lets send the target an IPI to kick it out of
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* nohz mode if necessary.
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*/
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static inline void sched_update_tick_dependency(struct rq *rq)
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{
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int cpu;
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if (!tick_nohz_full_enabled())
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return;
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cpu = cpu_of(rq);
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if (!tick_nohz_full_cpu(cpu))
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return;
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if (sched_can_stop_tick(rq))
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tick_nohz_dep_clear_cpu(cpu, TICK_DEP_BIT_SCHED);
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else
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tick_nohz_dep_set_cpu(cpu, TICK_DEP_BIT_SCHED);
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}
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#else
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static inline void sched_update_tick_dependency(struct rq *rq) { }
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#endif
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static inline void add_nr_running(struct rq *rq, unsigned count)
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{
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unsigned prev_nr = rq->nr_running;
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@ -1290,26 +1319,16 @@ static inline void add_nr_running(struct rq *rq, unsigned count)
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if (!rq->rd->overload)
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rq->rd->overload = true;
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#endif
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#ifdef CONFIG_NO_HZ_FULL
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if (tick_nohz_full_cpu(rq->cpu)) {
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/*
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* Tick is needed if more than one task runs on a CPU.
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* Send the target an IPI to kick it out of nohz mode.
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*
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* We assume that IPI implies full memory barrier and the
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* new value of rq->nr_running is visible on reception
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* from the target.
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*/
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tick_nohz_full_kick_cpu(rq->cpu);
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}
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#endif
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}
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sched_update_tick_dependency(rq);
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}
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static inline void sub_nr_running(struct rq *rq, unsigned count)
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{
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rq->nr_running -= count;
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/* Check if we still need preemption */
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sched_update_tick_dependency(rq);
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}
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static inline void rq_last_tick_reset(struct rq *rq)
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@ -204,11 +204,6 @@ static bool can_stop_full_tick(struct tick_sched *ts)
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return false;
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}
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if (!sched_can_stop_tick()) {
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trace_tick_stop(0, TICK_DEP_MASK_SCHED);
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return false;
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}
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if (!posix_cpu_timers_can_stop_tick(current)) {
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trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
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return false;
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