sched: Drop rq->lock from sched_exec()

Since we can now call select_task_rq() and set_task_cpu() with only
p->pi_lock held, and sched_exec() load-balancing has always been
optimistic, drop all rq->lock usage.

Oleg also noted that need_migrate_task() will always be true for
current, so don't bother calling that at all.

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110405152729.314204889@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 5 insertions, 10 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 7c5494dccd39..1be1a09b9dc9 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3465,27 +3465,22 @@ void sched_exec(void)
 {
         struct task_struct *p = current;
         unsigned long flags;
-        struct rq *rq;
         int dest_cpu;
 
-        rq = task_rq_lock(p, &flags);
+        raw_spin_lock_irqsave(&p->pi_lock, flags);
         dest_cpu = p->sched_class->select_task_rq(p, SD_BALANCE_EXEC, 0);
         if (dest_cpu == smp_processor_id())
                 goto unlock;
 
-        /*
-         * select_task_rq() can race against ->cpus_allowed
-         */
-        if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed) &&
-            likely(cpu_active(dest_cpu)) && need_migrate_task(p)) {
+        if (likely(cpu_active(dest_cpu))) {
                 struct migration_arg arg = { p, dest_cpu };
 
-                task_rq_unlock(rq, p, &flags);
-                stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg);
+                raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+                stop_one_cpu(task_cpu(p), migration_cpu_stop, &arg);
                 return;
         }
 unlock:
-        task_rq_unlock(rq, p, &flags);
+        raw_spin_unlock_irqrestore(&p->pi_lock, flags);
 }
 
 #endif