sched: Let the scheduler see CPU idle states (442bf3aa) · Commits · 戴 / test

When the cpu enters idle, it stores the cpuidle state pointer in its struct rq instance which in turn could be used to make a better decision when balancing tasks. As soon as the cpu exits its idle state, the struct rq reference is cleared. There are a couple of situations where the idle state pointer could be changed while it is being consulted: 1. For x86/acpi with dynamic c-states, when a laptop switches from battery to AC that could result on removing the deeper idle state. The acpi driver triggers: 'acpi_processor_cst_has_changed' 'cpuidle_pause_and_lock' 'cpuidle_uninstall_idle_handler' 'kick_all_cpus_sync'. All cpus will exit their idle state and the pointed object will be set to NULL. 2. The cpuidle driver is unloaded. Logically that could happen but not in practice because the drivers are always compiled in and 95% of them are not coded to unregister themselves. In any case, the unloading code must call 'cpuidle_unregister_device', that calls 'cpuidle_pause_and_lock' leading to 'kick_all_cpus_sync' as mentioned above. A race can happen if we use the pointer and then one of these two scenarios occurs at the same moment. In order to be safe, the idle state pointer stored in the rq must be used inside a rcu_read_lock section where we are protected with the 'rcu_barrier' in the 'cpuidle_uninstall_idle_handler' function. The idle_get_state() and idle_put_state() accessors should be used to that effect. Signed-off-by:

Daniel Lezcano <daniel.lezcano@linaro.org> Signed-off-by:

Nicolas Pitre <nico@linaro.org> Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: linux-pm@vger.kernel.org Cc: linaro-kernel@lists.linaro.org Cc: Daniel Lezcano <daniel.lezcano@linaro.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/n/tip-@git.kernel.org Signed-off-by:

Ingo Molnar <mingo@kernel.org>

drivers/cpuidle/cpuidle.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -225,6 +225,12 @@ void cpuidle_uninstall_idle_handler(void)
		initialized = 0;
		wake_up_all_idle_cpus();
		}

		/*
		* Make sure external observers (such as the scheduler)
		* are done looking at pointed idle states.
		*/
		synchronize_rcu();
		}

		/**

kernel/sched/idle.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -147,6 +147,9 @@ use_default:
		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu))
		goto use_default;

		/* Take note of the planned idle state. */
		idle_set_state(this_rq(), &drv->states[next_state]);

		/*
		* Enter the idle state previously returned by the governor decision.
		* This function will block until an interrupt occurs and will take
		@@ -154,6 +157,9 @@ use_default:
		*/
		entered_state = cpuidle_enter(drv, dev, next_state);

		/* The cpu is no longer idle or about to enter idle. */
		idle_set_state(this_rq(), NULL);

		if (broadcast)
		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);

kernel/sched/sched.h

+30 −0

Original line number	Diff line number	Diff line
		@@ -14,6 +14,7 @@
		#include "cpuacct.h"

		struct rq;
		struct cpuidle_state;

		/* task_struct::on_rq states: */
		#define TASK_ON_RQ_QUEUED 1
		@@ -643,6 +644,11 @@ struct rq {
		#ifdef CONFIG_SMP
		struct llist_head wake_list;
		#endif

		#ifdef CONFIG_CPU_IDLE
		/* Must be inspected within a rcu lock section */
		struct cpuidle_state *idle_state;
		#endif
		};

		static inline int cpu_of(struct rq *rq)
		@@ -1196,6 +1202,30 @@ static inline void idle_exit_fair(struct rq *rq) { }

		#endif

		#ifdef CONFIG_CPU_IDLE
		static inline void idle_set_state(struct rq *rq,
		struct cpuidle_state *idle_state)
		{
		rq->idle_state = idle_state;
		}

		static inline struct cpuidle_state idle_get_state(struct rq rq)
		{
		WARN_ON(!rcu_read_lock_held());
		return rq->idle_state;
		}
		#else
		static inline void idle_set_state(struct rq *rq,
		struct cpuidle_state *idle_state)
		{
		}

		static inline struct cpuidle_state idle_get_state(struct rq rq)
		{
		return NULL;
		}
		#endif

		extern void sysrq_sched_debug_show(void);
		extern void sched_init_granularity(void);
		extern void update_max_interval(void);

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