[PATCH 21/22] sched: Remove need_migrate_task()

Peter Zijlstra
2011-03-02T17:49:08Z

[-- Attachment #1: sched-opt-need_migrate_task.patch --]
[-- Type: text/plain, Size: 1569 bytes --]

Oleg noticed that need_migrate_task() doesn't need the ->on_cpu check
now that ttwu() doesn't do remote enqueues for !->on_rq && ->on_cpu,
so remove the helper and replace the single instance with a direct
->on_rq test.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
---
kernel/sched.c | 17 +----------------
1 file changed, 1 insertion(+), 16 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2139,21 +2139,6 @@ struct migration_arg {
static int migration_cpu_stop(void *data);

/*
- * The task's runqueue lock must be held.
- * Returns true if you have to wait for migration thread.
- */
-static bool need_migrate_task(struct task_struct *p)
-{
- /*
- * If the task is not on a runqueue (and not running), then
- * the next wake-up will properly place the task.
- */
- bool running = p->on_rq || p->on_cpu;
- smp_rmb(); /* finish_lock_switch() */
- return running;
-}
-
-/*
* wait_task_inactive - wait for a thread to unschedule.
*
* If @match_state is nonzero, it's the @p->state value just checked and
@@ -5734,7 +5719,7 @@ int set_cpus_allowed_ptr(struct task_str
goto out;

dest_cpu = cpumask_any_and(cpu_active_mask, new_mask);
- if (need_migrate_task(p)) {
+ if (p->on_rq) {
struct migration_arg arg = { p, dest_cpu };
/* Need help from migration thread: drop lock and wait. */
task_rq_unlock(rq, p, &flags);