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>

diff --git a/kernel/sched.c b/kernel/sched.c
index 7c5494dccd39416dddccd87b07b64631537e21c6..1be1a09b9dc993858b1f01099de79a0aef6e7471 100644 (file)
--- 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