Commit a26b89f0 authored by Markus Metzger's avatar Markus Metzger Committed by Ingo Molnar
Browse files

sched, hw-branch-tracer: add wait_task_context_switch() function to sched.h 



Add a function to wait until some other task has been
switched out at least once.

This differs from wait_task_inactive() subtly, in that the
latter will wait until the task has left the CPU.

Signed-off-by: default avatarMarkus Metzger <markus.t.metzger@intel.com>
Cc: markus.t.metzger@gmail.com
Cc: roland@redhat.com
Cc: eranian@googlemail.com
Cc: oleg@redhat.com
Cc: juan.villacis@intel.com
Cc: ak@linux.jf.intel.com
LKML-Reference: <20090403144549.794157000@intel.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent cac94f97

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1993,8 +1993,10 @@ extern void set_task_comm(struct task_struct *tsk, char *from); 
extern char *get_task_comm(char *to, struct task_struct *tsk);



#ifdef CONFIG_SMP

extern void wait_task_context_switch(struct task_struct *p);

extern unsigned long wait_task_inactive(struct task_struct *, long match_state);

#else

static inline void wait_task_context_switch(struct task_struct *p) {}

static inline unsigned long wait_task_inactive(struct task_struct *p,

					       long match_state)

{

kernel/sched.c

+43 −0
Original line number Diff line number Diff line
@@ -2002,6 +2002,49 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req) 
	return 1;

}



/*

 * wait_task_context_switch -	wait for a thread to complete at least one

 *				context switch.

 *

 * @p must not be current.

 */

void wait_task_context_switch(struct task_struct *p)

{

	unsigned long nvcsw, nivcsw, flags;

	int running;

	struct rq *rq;



	nvcsw	= p->nvcsw;

	nivcsw	= p->nivcsw;

	for (;;) {

		/*

		 * The runqueue is assigned before the actual context

		 * switch. We need to take the runqueue lock.

		 *

		 * We could check initially without the lock but it is

		 * very likely that we need to take the lock in every

		 * iteration.

		 */

		rq = task_rq_lock(p, &flags);

		running = task_running(rq, p);

		task_rq_unlock(rq, &flags);



		if (likely(!running))

			break;

		/*

		 * The switch count is incremented before the actual

		 * context switch. We thus wait for two switches to be

		 * sure at least one completed.

		 */

		if ((p->nvcsw - nvcsw) > 1)

			break;

		if ((p->nivcsw - nivcsw) > 1)

			break;



		cpu_relax();

	}

}



/*

 * wait_task_inactive - wait for a thread to unschedule.

 *

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