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Commit 9f479bdc authored by Junjie Wu's avatar Junjie Wu
Browse files

sched: Provide a wake up API without sending freq notifications 



Each time a task wakes up, scheduler evaluates its load and notifies
governor if the resulting frequency of destination CPU is larger than
a threshold. However, some governor wakes up a separate task that
handles frequency change, which again calls wake_up_process().

This is dangerous because if the task being woken up meets the
threshold and ends up being moved around, there is a potential for
endless recursive notifications.

Introduce a new API for waking up a task without triggering
frequency notification.

Change-Id: I24261af81b7dc410c7fb01eaa90920b8d66fbd2a
Signed-off-by: default avatarJunjie Wu <junjiew@codeaurora.org>
parent f9fb0d29

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -2459,6 +2459,7 @@ extern void xtime_update(unsigned long ticks); 


extern int wake_up_state(struct task_struct *tsk, unsigned int state);

extern int wake_up_process(struct task_struct *tsk);

extern int wake_up_process_no_notif(struct task_struct *tsk);

extern void wake_up_new_task(struct task_struct *tsk);

#ifdef CONFIG_SMP

 extern void kick_process(struct task_struct *tsk);

kernel/sched/core.c

+31 −5
Original line number Diff line number Diff line
@@ -4095,6 +4095,9 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) 
	u64 wallclock;

	struct related_thread_group *grp = NULL;

#endif

	bool freq_notif_allowed = !(wake_flags & WF_NO_NOTIFIER);



	wake_flags &= ~WF_NO_NOTIFIER;



	/*

	 * If we are going to wake up a thread waiting for CONDITION we
@@ -4185,11 +4188,14 @@ out: 
		atomic_notifier_call_chain(&migration_notifier_head,

					   0, (void *)&mnd);



	if (freq_notif_allowed) {

		if (!same_freq_domain(src_cpu, cpu)) {

			check_for_freq_change(cpu_rq(cpu));

			check_for_freq_change(cpu_rq(src_cpu));

	} else if (heavy_task)

		} else if (heavy_task) {

			check_for_freq_change(cpu_rq(cpu));

		}

	}



	return success;

}
@@ -4260,6 +4266,26 @@ int wake_up_process(struct task_struct *p) 
}

EXPORT_SYMBOL(wake_up_process);



/**

 * wake_up_process_no_notif - Wake up a specific process without notifying

 * governor

 * @p: The process to be woken up.

 *

 * Attempt to wake up the nominated process and move it to the set of runnable

 * processes.

 *

 * Return: 1 if the process was woken up, 0 if it was already running.

 *

 * It may be assumed that this function implies a write memory barrier before

 * changing the task state if and only if any tasks are woken up.

 */

int wake_up_process_no_notif(struct task_struct *p)

{

	WARN_ON(task_is_stopped_or_traced(p));

	return try_to_wake_up(p, TASK_NORMAL, WF_NO_NOTIFIER);

}

EXPORT_SYMBOL(wake_up_process_no_notif);



int wake_up_state(struct task_struct *p, unsigned int state)

{

	return try_to_wake_up(p, state, 0);

kernel/sched/qhmp_core.c

+31 −5
Original line number Diff line number Diff line
@@ -3460,6 +3460,9 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) 
	struct rq *rq;

	u64 wallclock;

#endif

	bool freq_notif_allowed = !(wake_flags & WF_NO_NOTIFIER);



	wake_flags &= ~WF_NO_NOTIFIER;



	/*

	 * If we are going to wake up a thread waiting for CONDITION we
@@ -3546,11 +3549,14 @@ out: 
		atomic_notifier_call_chain(&migration_notifier_head,

					   0, (void *)&mnd);



	if (freq_notif_allowed) {

		if (!same_freq_domain(src_cpu, cpu)) {

			check_for_freq_change(cpu_rq(cpu));

			check_for_freq_change(cpu_rq(src_cpu));

	} else if (heavy_task)

		} else if (heavy_task) {

			check_for_freq_change(cpu_rq(cpu));

		}

	}



	return success;

}
@@ -3620,6 +3626,26 @@ int wake_up_process(struct task_struct *p) 
}

EXPORT_SYMBOL(wake_up_process);



/**

 * wake_up_process_no_notif - Wake up a specific process without notifying

 * governor

 * @p: The process to be woken up.

 *

 * Attempt to wake up the nominated process and move it to the set of runnable

 * processes.

 *

 * Return: 1 if the process was woken up, 0 if it was already running.

 *

 * It may be assumed that this function implies a write memory barrier before

 * changing the task state if and only if any tasks are woken up.

 */

int wake_up_process_no_notif(struct task_struct *p)

{

	WARN_ON(task_is_stopped_or_traced(p));

	return try_to_wake_up(p, TASK_NORMAL, WF_NO_NOTIFIER);

}

EXPORT_SYMBOL(wake_up_process_no_notif);



int wake_up_state(struct task_struct *p, unsigned int state)

{

	return try_to_wake_up(p, state, 0);

kernel/sched/qhmp_sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1374,6 +1374,7 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev) 
#define WF_SYNC		0x01		/* waker goes to sleep after wakeup */

#define WF_FORK		0x02		/* child wakeup after fork */

#define WF_MIGRATED	0x4		/* internal use, task got migrated */

#define WF_NO_NOTIFIER	0x08		/* do not notify governor */



/*

 * To aid in avoiding the subversion of "niceness" due to uneven distribution

kernel/sched/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -1515,6 +1515,7 @@ static inline void finish_lock_switch(struct rq *rq, struct task_struct *prev) 
#define WF_SYNC		0x01		/* waker goes to sleep after wakeup */

#define WF_FORK		0x02		/* child wakeup after fork */

#define WF_MIGRATED	0x4		/* internal use, task got migrated */

#define WF_NO_NOTIFIER	0x08		/* do not notify governor */



/*

 * To aid in avoiding the subversion of "niceness" due to uneven distribution