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: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched.c b/kernel/sched.c
index 6deff24..f7dee20 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6112,52 +6112,46 @@
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;
}
/*
