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Commit e76bd8d9 authored by Rusty Russell's avatar Rusty Russell Committed by Ingo Molnar
Browse files

sched: avoid stack var in move_task_off_dead_cpu 



Impact: stack usage reduction

With some care, we can avoid needing a temporary cpumask (we can't
really allocate here, since we can't fail).

This version calls cpuset_cpus_allowed_locked() with the task_rq_lock
held.  I'm fairly sure this works, but there might be a deadlock
hiding.

And of course, we can't get rid of the last cpumask on stack until we
can use cpumask_of_node instead of node_to_cpumask.

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent f17c8607

kernel/sched.c

+36 −42
Original line number Diff line number Diff line
@@ -6112,38 +6112,28 @@ static int __migrate_task_irq(struct task_struct *p, int src_cpu, int dest_cpu) 
static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p)

{

	unsigned long flags;

	cpumask_t mask;

	struct rq *rq;

	int dest_cpu;

	/* FIXME: Use cpumask_of_node here. */

	cpumask_t _nodemask = node_to_cpumask(cpu_to_node(dead_cpu));

	const struct cpumask *nodemask = &_nodemask;



	do {

		/* On same node? */

		node_to_cpumask_ptr(pnodemask, cpu_to_node(dead_cpu));



		cpus_and(mask, *pnodemask, p->cpus_allowed);

		dest_cpu = cpumask_any_and(cpu_online_mask, &mask);

again:

	/* Look for allowed, online CPU in same node. */

	for_each_cpu_and(dest_cpu, nodemask, cpu_online_mask)

		if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed))

			goto move;



		/* On any allowed CPU? */

		if (dest_cpu >= nr_cpu_ids)

			dest_cpu = cpumask_any_and(cpu_online_mask,

						   &p->cpus_allowed);

	/* Any allowed, online CPU? */

	dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_online_mask);

	if (dest_cpu < nr_cpu_ids)

		goto move;



	/* No more Mr. Nice Guy. */

	if (dest_cpu >= nr_cpu_ids) {

			cpumask_t cpus_allowed;



			cpuset_cpus_allowed_locked(p, &cpus_allowed);

			/*

			 * Try to stay on the same cpuset, where the

			 * current cpuset may be a subset of all cpus.

			 * The cpuset_cpus_allowed_locked() variant of

			 * cpuset_cpus_allowed() will not block. It must be

			 * called within calls to cpuset_lock/cpuset_unlock.

			 */

		rq = task_rq_lock(p, &flags);

			p->cpus_allowed = cpus_allowed;

			dest_cpu = cpumask_any_and(cpu_online_mask,

						    &p->cpus_allowed);

		cpuset_cpus_allowed_locked(p, &p->cpus_allowed);

		dest_cpu = cpumask_any_and(cpu_online_mask, &p->cpus_allowed);

		task_rq_unlock(rq, &flags);



		/*
@@ -6157,7 +6147,11 @@ static void move_task_off_dead_cpu(int dead_cpu, struct task_struct *p) 
			       task_pid_nr(p), p->comm, dead_cpu);

		}

	}

	} while (!__migrate_task_irq(p, dead_cpu, dest_cpu));



move:

	/* It can have affinity changed while we were choosing. */

	if (unlikely(!__migrate_task_irq(p, dead_cpu, dest_cpu)))

		goto again;

}



/*