sched: Drop the rq argument to sched_class::select_task_rq()

In preparation of calling select_task_rq() without rq->lock held, drop
the dependency on the rq argument.

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/20110405152729.031077745@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index b33a700..ff4e2f9 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1067,8 +1067,7 @@ struct sched_class {
        void (*put_prev_task) (struct rq *rq, struct task_struct *p);
 
 #ifdef CONFIG_SMP
-       int  (*select_task_rq)(struct rq *rq, struct task_struct *p,
-                              int sd_flag, int flags);
+       int  (*select_task_rq)(struct task_struct *p, int sd_flag, int flags);
 
        void (*pre_schedule) (struct rq *this_rq, struct task_struct *task);
        void (*post_schedule) (struct rq *this_rq);

diff --git a/kernel/sched.c b/kernel/sched.c
index d398f2f..d4b815d 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2195,13 +2195,15 @@ 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 migrate_task(struct task_struct *p, struct rq *rq)
+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.
         */
-       return p->on_rq || task_running(rq, p);
+       bool running = p->on_rq || p->on_cpu;
+       smp_rmb(); /* finish_lock_switch() */
+       return running;
 }
 
 /*
@@ -2376,9 +2378,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
  * The caller (fork, wakeup) owns p->pi_lock, ->cpus_allowed is stable.
  */
 static inline
-int select_task_rq(struct rq *rq, struct task_struct *p, int sd_flags, int wake_flags)
+int select_task_rq(struct task_struct *p, int sd_flags, int wake_flags)
 {
-       int cpu = p->sched_class->select_task_rq(rq, p, sd_flags, wake_flags);
+       int cpu = p->sched_class->select_task_rq(p, sd_flags, wake_flags);
 
        /*
         * In order not to call set_task_cpu() on a blocking task we need
@@ -2533,7 +2535,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state,
                en_flags |= ENQUEUE_WAKING;
        }
 
-       cpu = select_task_rq(rq, p, SD_BALANCE_WAKE, wake_flags);
+       cpu = select_task_rq(p, SD_BALANCE_WAKE, wake_flags);
        if (cpu != orig_cpu)
                set_task_cpu(p, cpu);
        __task_rq_unlock(rq);
@@ -2744,7 +2746,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
         * We set TASK_WAKING so that select_task_rq() can drop rq->lock
         * without people poking at ->cpus_allowed.
         */
-       cpu = select_task_rq(rq, p, SD_BALANCE_FORK, 0);
+       cpu = select_task_rq(p, SD_BALANCE_FORK, 0);
        set_task_cpu(p, cpu);
 
        p->state = TASK_RUNNING;
@@ -3474,7 +3476,7 @@ void sched_exec(void)
        int dest_cpu;
 
        rq = task_rq_lock(p, &flags);
-       dest_cpu = p->sched_class->select_task_rq(rq, p, SD_BALANCE_EXEC, 0);
+       dest_cpu = p->sched_class->select_task_rq(p, SD_BALANCE_EXEC, 0);
        if (dest_cpu == smp_processor_id())
                goto unlock;
 
@@ -3482,7 +3484,7 @@ void sched_exec(void)
         * select_task_rq() can race against ->cpus_allowed
         */
        if (cpumask_test_cpu(dest_cpu, &p->cpus_allowed) &&
-           likely(cpu_active(dest_cpu)) && migrate_task(p, rq)) {
+           likely(cpu_active(dest_cpu)) && need_migrate_task(p)) {
                struct migration_arg arg = { p, dest_cpu };
 
                task_rq_unlock(rq, &flags);
@@ -5911,7 +5913,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
                goto out;
 
        dest_cpu = cpumask_any_and(cpu_active_mask, new_mask);
-       if (migrate_task(p, rq)) {
+       if (need_migrate_task(p)) {
                struct migration_arg arg = { p, dest_cpu };
                /* Need help from migration thread: drop lock and wait. */
                __task_rq_unlock(rq);

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 4ee50f0..96b2c95 100644 (file)
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1657,7 +1657,7 @@ static int select_idle_sibling(struct task_struct *p, int target)
  * preempt must be disabled.
  */
 static int
-select_task_rq_fair(struct rq *rq, struct task_struct *p, int sd_flag, int wake_flags)
+select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
 {
        struct sched_domain *tmp, *affine_sd = NULL, *sd = NULL;
        int cpu = smp_processor_id();

diff --git a/kernel/sched_idletask.c b/kernel/sched_idletask.c
index a776a63..0a51882 100644 (file)
--- a/kernel/sched_idletask.c
+++ b/kernel/sched_idletask.c
@@ -7,7 +7,7 @@
 
 #ifdef CONFIG_SMP
 static int
-select_task_rq_idle(struct rq *rq, struct task_struct *p, int sd_flag, int flags)
+select_task_rq_idle(struct task_struct *p, int sd_flag, int flags)
 {
        return task_cpu(p); /* IDLE tasks as never migrated */
 }

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 9ca4f5f..19ecb31 100644 (file)
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -977,13 +977,23 @@ static void yield_task_rt(struct rq *rq)
 static int find_lowest_rq(struct task_struct *task);
 
 static int
-select_task_rq_rt(struct rq *rq, struct task_struct *p, int sd_flag, int flags)
+select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)
 {
+       struct task_struct *curr;
+       struct rq *rq;
+       int cpu;
+
        if (sd_flag != SD_BALANCE_WAKE)
                return smp_processor_id();
 
+       cpu = task_cpu(p);
+       rq = cpu_rq(cpu);
+
+       rcu_read_lock();
+       curr = ACCESS_ONCE(rq->curr); /* unlocked access */
+
        /*
-        * If the current task is an RT task, then
+        * If the current task on @p's runqueue is an RT task, then
         * try to see if we can wake this RT task up on another
         * runqueue. Otherwise simply start this RT task
         * on its current runqueue.
@@ -997,21 +1007,25 @@ select_task_rq_rt(struct rq *rq, struct task_struct *p, int sd_flag, int flags)
         * lock?
         *
         * For equal prio tasks, we just let the scheduler sort it out.
+        *
+        * Otherwise, just let it ride on the affined RQ and the
+        * post-schedule router will push the preempted task away
+        *
+        * This test is optimistic, if we get it wrong the load-balancer
+        * will have to sort it out.
         */
-       if (unlikely(rt_task(rq->curr)) &&
-           (rq->curr->rt.nr_cpus_allowed < 2 ||
-            rq->curr->prio < p->prio) &&
+       if (curr && unlikely(rt_task(curr)) &&
+           (curr->rt.nr_cpus_allowed < 2 ||
+            curr->prio < p->prio) &&
            (p->rt.nr_cpus_allowed > 1)) {
-               int cpu = find_lowest_rq(p);
+               int target = find_lowest_rq(p);
 
-               return (cpu == -1) ? task_cpu(p) : cpu;
+               if (target != -1)
+                       cpu = target;
        }
+       rcu_read_unlock();
 
-       /*
-        * Otherwise, just let it ride on the affined RQ and the
-        * post-schedule router will push the preempted task away
-        */
-       return task_cpu(p);
+       return cpu;
 }
 
 static void check_preempt_equal_prio(struct rq *rq, struct task_struct *p)

diff --git a/kernel/sched_stoptask.c b/kernel/sched_stoptask.c
index f607de4..6f43763 100644 (file)
--- a/kernel/sched_stoptask.c
+++ b/kernel/sched_stoptask.c
@@ -9,8 +9,7 @@
 
 #ifdef CONFIG_SMP
 static int
-select_task_rq_stop(struct rq *rq, struct task_struct *p,
-                   int sd_flag, int flags)
+select_task_rq_stop(struct task_struct *p, int sd_flag, int flags)
 {
        return task_cpu(p); /* stop tasks as never migrate */
 }