nohz: Re-evaluate the tick for the new task after a context switch (99e5ada9) · Commits · 戴 / test

When a task is scheduled in, it may have some properties of its own that could make the CPU reconsider the need for the tick: posix cpu timers, perf events, ... So notify the full dynticks subsystem when a task gets scheduled in and re-check the tick dependency at this stage. This is done through a self IPI to avoid messing up with any current lock scenario. Signed-off-by:

Frederic Weisbecker <fweisbec@gmail.com> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kevin Hilman <khilman@linaro.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>

include/linux/tick.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -163,12 +163,14 @@ extern int tick_nohz_full_cpu(int cpu);
		extern void tick_nohz_full_check(void);
		extern void tick_nohz_full_kick(void);
		extern void tick_nohz_full_kick_all(void);
		extern void tick_nohz_task_switch(struct task_struct *tsk);
		#else
		static inline void tick_nohz_init(void) { }
		static inline int tick_nohz_full_cpu(int cpu) { return 0; }
		static inline void tick_nohz_full_check(void) { }
		static inline void tick_nohz_full_kick(void) { }
		static inline void tick_nohz_full_kick_all(void) { }
		static inline void tick_nohz_task_switch(struct task_struct *tsk) { }
		#endif

kernel/sched/core.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -1896,6 +1896,8 @@ static void finish_task_switch(struct rq rq, struct task_struct prev)
		kprobe_flush_task(prev);
		put_task_struct(prev);
		}

		tick_nohz_task_switch(current);
		}

		#ifdef CONFIG_SMP

kernel/time/tick-sched.c

+20 −0

Original line number	Diff line number	Diff line
		@@ -232,6 +232,26 @@ void tick_nohz_full_kick_all(void)
		preempt_enable();
		}

		/*
		* Re-evaluate the need for the tick as we switch the current task.
		* It might need the tick due to per task/process properties:
		* perf events, posix cpu timers, ...
		*/
		void tick_nohz_task_switch(struct task_struct *tsk)
		{
		unsigned long flags;

		if (!tick_nohz_full_cpu(smp_processor_id()))
		return;

		local_irq_save(flags);

		if (tick_nohz_tick_stopped() && !can_stop_full_tick())
		tick_nohz_full_kick();

		local_irq_restore(flags);
		}

		int tick_nohz_full_cpu(int cpu)
		{
		if (!have_nohz_full_mask)

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