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sched: avoid stack var in move_task_off_dead_cpu

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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: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Rusty Russell 2008-11-25 02:35:11 +10:30 committed by Ingo Molnar
parent f17c860760
commit e76bd8d985
1 changed files with 33 additions and 39 deletions
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72
kernel/sched.c
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@ -6112,52 +6112,46 @@ 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));
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;
cpus_and(mask, *pnodemask, p->cpus_allowed);
dest_cpu = cpumask_any_and(cpu_online_mask, &mask);
/* Any allowed, online CPU? */
dest_cpu = cpumask_any_and(&p->cpus_allowed, cpu_online_mask);
if (dest_cpu < nr_cpu_ids)
goto move;
/* On any allowed CPU? */
if (dest_cpu >= nr_cpu_ids)
dest_cpu = cpumask_any_and(cpu_online_mask,
&p->cpus_allowed);
/* No more Mr. Nice Guy. */
if (dest_cpu >= nr_cpu_ids) {
rq = task_rq_lock(p, &flags);
cpuset_cpus_allowed_locked(p, &p->cpus_allowed);
dest_cpu = cpumask_any_and(cpu_online_mask, &p->cpus_allowed);
task_rq_unlock(rq, &flags);
/* 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);
task_rq_unlock(rq, &flags);
/*
* Don't tell them about moving exiting tasks or
* kernel threads (both mm NULL), since they never
* leave kernel.
*/
if (p->mm && printk_ratelimit()) {
printk(KERN_INFO "process %d (%s) no "
"longer affine to cpu%d\n",
task_pid_nr(p), p->comm, dead_cpu);
}
/*
* Don't tell them about moving exiting tasks or
* kernel threads (both mm NULL), since they never
* leave kernel.
*/
if (p->mm && printk_ratelimit()) {
printk(KERN_INFO "process %d (%s) no "
"longer affine to cpu%d\n",
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;
}
/*