Commit ac66f547 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched/numa: Introduce migrate_swap() 



Use the new stop_two_cpus() to implement migrate_swap(), a function that
flips two tasks between their respective cpus.

I'm fairly sure there's a less crude way than employing the stop_two_cpus()
method, but everything I tried either got horribly fragile and/or complex. So
keep it simple for now.

The notable detail is how we 'migrate' tasks that aren't runnable
anymore. We'll make it appear like we migrated them before they went to
sleep. The sole difference is the previous cpu in the wakeup path, so we
override this.

Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Reviewed-by: default avatarRik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/r/1381141781-10992-39-git-send-email-mgorman@suse.de


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1be0bd77

include/linux/sched.h

+2 −0
Original line number Diff line number Diff line
@@ -1043,6 +1043,8 @@ struct task_struct { 
	struct task_struct *last_wakee;

	unsigned long wakee_flips;

	unsigned long wakee_flip_decay_ts;



	int wake_cpu;

#endif

	int on_rq;

kernel/sched/core.c

+101 −5
Original line number Diff line number Diff line
@@ -1013,6 +1013,102 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu) 
	__set_task_cpu(p, new_cpu);

}



static void __migrate_swap_task(struct task_struct *p, int cpu)

{

	if (p->on_rq) {

		struct rq *src_rq, *dst_rq;



		src_rq = task_rq(p);

		dst_rq = cpu_rq(cpu);



		deactivate_task(src_rq, p, 0);

		set_task_cpu(p, cpu);

		activate_task(dst_rq, p, 0);

		check_preempt_curr(dst_rq, p, 0);

	} else {

		/*

		 * Task isn't running anymore; make it appear like we migrated

		 * it before it went to sleep. This means on wakeup we make the

		 * previous cpu our targer instead of where it really is.

		 */

		p->wake_cpu = cpu;

	}

}



struct migration_swap_arg {

	struct task_struct *src_task, *dst_task;

	int src_cpu, dst_cpu;

};



static int migrate_swap_stop(void *data)

{

	struct migration_swap_arg *arg = data;

	struct rq *src_rq, *dst_rq;

	int ret = -EAGAIN;



	src_rq = cpu_rq(arg->src_cpu);

	dst_rq = cpu_rq(arg->dst_cpu);



	double_rq_lock(src_rq, dst_rq);

	if (task_cpu(arg->dst_task) != arg->dst_cpu)

		goto unlock;



	if (task_cpu(arg->src_task) != arg->src_cpu)

		goto unlock;



	if (!cpumask_test_cpu(arg->dst_cpu, tsk_cpus_allowed(arg->src_task)))

		goto unlock;



	if (!cpumask_test_cpu(arg->src_cpu, tsk_cpus_allowed(arg->dst_task)))

		goto unlock;



	__migrate_swap_task(arg->src_task, arg->dst_cpu);

	__migrate_swap_task(arg->dst_task, arg->src_cpu);



	ret = 0;



unlock:

	double_rq_unlock(src_rq, dst_rq);



	return ret;

}



/*

 * Cross migrate two tasks

 */

int migrate_swap(struct task_struct *cur, struct task_struct *p)

{

	struct migration_swap_arg arg;

	int ret = -EINVAL;



	get_online_cpus();



	arg = (struct migration_swap_arg){

		.src_task = cur,

		.src_cpu = task_cpu(cur),

		.dst_task = p,

		.dst_cpu = task_cpu(p),

	};



	if (arg.src_cpu == arg.dst_cpu)

		goto out;



	if (!cpu_active(arg.src_cpu) || !cpu_active(arg.dst_cpu))

		goto out;



	if (!cpumask_test_cpu(arg.dst_cpu, tsk_cpus_allowed(arg.src_task)))

		goto out;



	if (!cpumask_test_cpu(arg.src_cpu, tsk_cpus_allowed(arg.dst_task)))

		goto out;



	ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);



out:

	put_online_cpus();

	return ret;

}



struct migration_arg {

	struct task_struct *task;

	int dest_cpu;
@@ -1232,9 +1328,9 @@ out: 
 * The caller (fork, wakeup) owns p->pi_lock, ->cpus_allowed is stable.

 */

static inline

int select_task_rq(struct task_struct *p, int sd_flags, int wake_flags)

int select_task_rq(struct task_struct *p, int cpu, int sd_flags, int wake_flags)

{

	int cpu = p->sched_class->select_task_rq(p, sd_flags, wake_flags);

	cpu = p->sched_class->select_task_rq(p, cpu, sd_flags, wake_flags);



	/*

	 * In order not to call set_task_cpu() on a blocking task we need
@@ -1518,7 +1614,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) 
	if (p->sched_class->task_waking)

		p->sched_class->task_waking(p);



	cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags);

	cpu = select_task_rq(p, p->wake_cpu, SD_BALANCE_WAKE, wake_flags);

	if (task_cpu(p) != cpu) {

		wake_flags |= WF_MIGRATED;

		set_task_cpu(p, cpu);
@@ -1752,7 +1848,7 @@ void wake_up_new_task(struct task_struct *p) 
	 *  - cpus_allowed can change in the fork path

	 *  - any previously selected cpu might disappear through hotplug

	 */

	set_task_cpu(p, select_task_rq(p, SD_BALANCE_FORK, 0));

	set_task_cpu(p, select_task_rq(p, task_cpu(p), SD_BALANCE_FORK, 0));

#endif



	/* Initialize new task's runnable average */
@@ -2080,7 +2176,7 @@ void sched_exec(void) 
	int dest_cpu;



	raw_spin_lock_irqsave(&p->pi_lock, flags);

	dest_cpu = p->sched_class->select_task_rq(p, SD_BALANCE_EXEC, 0);

	dest_cpu = p->sched_class->select_task_rq(p, task_cpu(p), SD_BALANCE_EXEC, 0);

	if (dest_cpu == smp_processor_id())

		goto unlock;

kernel/sched/fair.c

+1 −2
Original line number Diff line number Diff line
@@ -3706,11 +3706,10 @@ done: 
 * preempt must be disabled.

 */

static int

select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)

select_task_rq_fair(struct task_struct *p, int prev_cpu, int sd_flag, int wake_flags)

{

	struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;

	int cpu = smp_processor_id();

	int prev_cpu = task_cpu(p);

	int new_cpu = cpu;

	int want_affine = 0;

	int sync = wake_flags & WF_SYNC;

kernel/sched/idle_task.c

+1 −1
Original line number Diff line number Diff line
@@ -9,7 +9,7 @@ 


#ifdef CONFIG_SMP

static int

select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)

select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags)

{

	return task_cpu(p); /* IDLE tasks as never migrated */

}

kernel/sched/rt.c

+1 −4
Original line number Diff line number Diff line
@@ -1169,13 +1169,10 @@ static void yield_task_rt(struct rq *rq) 
static int find_lowest_rq(struct task_struct *task);



static int

select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)

select_task_rq_rt(struct task_struct *p, int cpu, int sd_flag, int flags)

{

	struct task_struct *curr;

	struct rq *rq;

	int cpu;



	cpu = task_cpu(p);



	if (p->nr_cpus_allowed == 1)

		goto out;

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