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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Chris Mason <chris.mason@oracle.com>,
	Frank Rowand <frank.rowand@am.sony.com>,
	Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
	Mike Galbraith <efault@gmx.de>, Oleg Nesterov <oleg@redhat.com>,
	Paul Turner <pjt@google.com>, Jens Axboe <axboe@kernel.dk>,
	Yong Zhang <yong.zhang0@gmail.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: [PATCH 08/21] sched: Drop the rq argument to sched_class::select_task_rq()
Date: Tue, 05 Apr 2011 17:23:46 +0200
Message-ID: <20110405152729.031077745@chello.nl> (raw)
In-Reply-To: <20110405152338.692966333@chello.nl>

[-- Attachment #0: sched-select_task_rq.patch --]
[-- Type: text/plain, Size: 7480 bytes --]

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

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
---
 include/linux/sched.h   |    3 +--
 kernel/sched.c          |   20 +++++++++++---------
 kernel/sched_fair.c     |    2 +-
 kernel/sched_idletask.c |    2 +-
 kernel/sched_rt.c       |   38 ++++++++++++++++++++++++++------------
 kernel/sched_stoptask.c |    3 +--
 6 files changed, 41 insertions(+), 27 deletions(-)

Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1063,8 +1063,7 @@ 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);
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2138,13 +2138,15 @@ 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;
 }
 
 /*
@@ -2337,9 +2339,9 @@ static int select_fallback_rq(int cpu, s
  * 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
@@ -2484,7 +2486,7 @@ static int try_to_wake_up(struct task_st
 		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);
@@ -2694,7 +2696,7 @@ void wake_up_new_task(struct task_struct
 	 * 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;
@@ -3420,7 +3422,7 @@ 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;
 
@@ -3428,7 +3430,7 @@ 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);
@@ -5681,7 +5683,7 @@ int set_cpus_allowed_ptr(struct task_str
 		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);
Index: linux-2.6/kernel/sched_fair.c
===================================================================
--- linux-2.6.orig/kernel/sched_fair.c
+++ linux-2.6/kernel/sched_fair.c
@@ -1623,7 +1623,7 @@ static int select_idle_sibling(struct ta
  * 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();
Index: linux-2.6/kernel/sched_idletask.c
===================================================================
--- linux-2.6.orig/kernel/sched_idletask.c
+++ linux-2.6/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 */
 }
Index: linux-2.6/kernel/sched_rt.c
===================================================================
--- linux-2.6.orig/kernel/sched_rt.c
+++ linux-2.6/kernel/sched_rt.c
@@ -973,13 +973,23 @@ 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.
@@ -993,21 +1003,25 @@ select_task_rq_rt(struct rq *rq, struct 
 	 * 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)
Index: linux-2.6/kernel/sched_stoptask.c
===================================================================
--- linux-2.6.orig/kernel/sched_stoptask.c
+++ linux-2.6/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 */
 }



  parent reply index

Thread overview: 152+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-05 15:23 [PATCH 00/21] sched: Reduce runqueue lock contention -v6 Peter Zijlstra
2011-04-05 15:23 ` [PATCH 01/21] sched: Provide scheduler_ipi() callback in response to smp_send_reschedule() Peter Zijlstra
2011-04-13 21:15   ` Tony Luck
2011-04-13 21:38     ` Peter Zijlstra
2011-04-14  8:31   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 02/21] sched: Always provide p->on_cpu Peter Zijlstra
2011-04-14  8:31   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 03/21] mutex: Use p->on_cpu for the adaptive spin Peter Zijlstra
2011-04-14  8:32   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 04/21] sched: Change the ttwu success details Peter Zijlstra
2011-04-13  9:23   ` Peter Zijlstra
2011-04-13 10:48     ` Peter Zijlstra
2011-04-13 11:06       ` Peter Zijlstra
2011-04-13 18:39         ` Tejun Heo
2011-04-13 19:11           ` Peter Zijlstra
2011-04-14  8:32   ` [tip:sched/locking] sched: Change the ttwu() " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 05/21] sched: Clean up ttwu stats Peter Zijlstra
2011-04-14  8:33   ` [tip:sched/locking] sched: Clean up ttwu() stats tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 06/21] sched: Provide p->on_rq Peter Zijlstra
2011-04-14  8:33   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 07/21] sched: Serialize p->cpus_allowed and ttwu() using p->pi_lock Peter Zijlstra
2011-04-14  8:34   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` Peter Zijlstra [this message]
2011-04-14  8:34   ` [tip:sched/locking] sched: Drop the rq argument to sched_class::select_task_rq() tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 09/21] sched: Remove rq argument to sched_class::task_waking() Peter Zijlstra
2011-04-14  8:35   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 10/21] sched: Deal with non-atomic min_vruntime reads on 32bits Peter Zijlstra
2011-04-14  8:35   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 11/21] sched: Delay task_contributes_to_load() Peter Zijlstra
2011-04-14  8:35   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 12/21] sched: Also serialize ttwu_local() with p->pi_lock Peter Zijlstra
2011-04-14  8:36   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 13/21] sched: Add p->pi_lock to task_rq_lock() Peter Zijlstra
2011-04-14  8:36   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-06-01 13:58     ` Arne Jansen
2011-06-01 16:35       ` Peter Zijlstra
2011-06-01 17:20         ` Arne Jansen
2011-06-01 18:09           ` Peter Zijlstra
2011-06-01 18:44             ` Peter Zijlstra
2011-06-01 19:30               ` Arne Jansen
2011-06-01 21:09                 ` Linus Torvalds
2011-06-03  9:15                   ` Peter Zijlstra
2011-06-03 10:02                     ` Arne Jansen
2011-06-03 10:30                       ` Peter Zijlstra
2011-06-03 11:52                         ` Arne Jansen
2011-06-05  8:17                         ` Ingo Molnar
2011-06-05  8:53                           ` Arne Jansen
2011-06-05  9:41                             ` Ingo Molnar
2011-06-05  9:45                               ` Ingo Molnar
2011-06-05  9:43                           ` Arne Jansen
2011-06-05  9:55                             ` Ingo Molnar
2011-06-05 10:22                               ` Arne Jansen
2011-06-05 11:01                                 ` Ingo Molnar
2011-06-05 11:19                                   ` [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages Ingo Molnar
2011-06-05 11:36                                     ` Ingo Molnar
2011-06-05 11:57                                       ` Arne Jansen
2011-06-05 13:39                                         ` Ingo Molnar
2011-06-05 13:54                                           ` Arne Jansen
2011-06-05 14:06                                             ` Ingo Molnar
2011-06-05 14:45                                               ` Arne Jansen
2011-06-05 14:10                                             ` Ingo Molnar
2011-06-05 14:31                                               ` Arne Jansen
2011-06-05 15:13                                                 ` Ingo Molnar
2011-06-05 15:26                                                   ` Ingo Molnar
2011-06-05 15:32                                                     ` Ingo Molnar
2011-06-05 16:07                                                       ` Arne Jansen
2011-06-05 16:35                                                         ` Arne Jansen
2011-06-05 16:50                                                           ` Arne Jansen
2011-06-05 17:20                                                             ` Ingo Molnar
2011-06-05 17:42                                                               ` Arne Jansen
2011-06-05 18:59                                                                 ` Ingo Molnar
2011-06-05 19:30                                                                   ` Arne Jansen
2011-06-05 19:44                                                                     ` Ingo Molnar
2011-06-05 20:15                                                                       ` Arne Jansen
2011-06-06  6:56                                                                         ` Arne Jansen
2011-06-06  9:01                                                                         ` Peter Zijlstra
2011-06-06  9:18                                                                           ` Arne Jansen
2011-06-06  9:24                                                                             ` Peter Zijlstra
2011-06-06  9:52                                                                               ` Peter Zijlstra
2011-06-06 10:00                                                                           ` Arne Jansen
2011-06-06 10:26                                                                             ` Peter Zijlstra
2011-06-06 13:25                                                                               ` Peter Zijlstra
2011-06-06 15:04                                                                           ` Ingo Molnar
2011-06-06 15:08                                                                             ` Ingo Molnar
2011-06-06 17:44                                                                               ` Mike Galbraith
2011-06-07  5:20                                                                           ` Mike Galbraith
2011-06-06 13:10                                                                   ` Ingo Molnar
2011-06-06 13:12                                                                     ` Peter Zijlstra
2011-06-06 13:21                                                                       ` Ingo Molnar
2011-06-06 13:31                                                                         ` Peter Zijlstra
2011-06-06  7:34                                                     ` Arne Jansen
2011-06-05 15:34                                                   ` Arne Jansen
2011-06-06  8:38                                                   ` Peter Zijlstra
2011-06-06 14:58                                                     ` Ingo Molnar
2011-06-06 15:09                                                       ` Peter Zijlstra
2011-06-06 15:47                                                         ` Peter Zijlstra
2011-06-06 15:52                                                           ` Ingo Molnar
2011-06-06 16:00                                                             ` Peter Zijlstra
2011-06-06 16:08                                                               ` Ingo Molnar
2011-06-06 16:12                                                                 ` Peter Zijlstra
2011-06-06 16:17                                                                   ` Ingo Molnar
2011-06-06 16:38                                                                     ` Arne Jansen
2011-06-06 16:45                                                                       ` Arne Jansen
2011-06-06 16:53                                                                         ` Peter Zijlstra
2011-06-06 17:07                                                                         ` Ingo Molnar
2011-06-06 17:11                                                                           ` Peter Zijlstra
2011-06-08 15:50                                                                             ` Peter Zijlstra
2011-06-08 19:17                                                                               ` Ingo Molnar
2011-06-08 19:27                                                                                 ` Linus Torvalds
2011-06-08 20:32                                                                                   ` Peter Zijlstra
2011-06-08 20:53                                                                                     ` Linus Torvalds
2011-06-08 20:54                                                                                     ` Thomas Gleixner
2011-06-08 19:45                                                                                 ` Peter Zijlstra
2011-06-08 20:52                                                                                   ` Ingo Molnar
2011-06-08 21:49                                                                                     ` Peter Zijlstra
2011-06-08 21:57                                                                                       ` Thomas Gleixner
2011-06-06 16:44                                                                     ` Peter Zijlstra
2011-06-06 16:50                                                                       ` Peter Zijlstra
2011-06-06 17:13                                                                         ` Ingo Molnar
2011-06-06 17:04                                                                       ` Peter Zijlstra
2011-06-06 17:11                                                                       ` Ingo Molnar
2011-06-06 17:57                                                                         ` Arne Jansen
2011-06-06 18:07                                                                           ` Ingo Molnar
2011-06-06 18:14                                                                             ` Arne Jansen
2011-06-06 18:19                                                                             ` Peter Zijlstra
2011-06-06 22:08                                                                               ` Ingo Molnar
2011-06-03 12:44                       ` [tip:sched/locking] sched: Add p->pi_lock to task_rq_lock() Linus Torvalds
2011-06-03 13:05                         ` Arne Jansen
2011-06-04 21:29                           ` Linus Torvalds
2011-06-04 22:08                             ` Peter Zijlstra
2011-06-04 22:50                               ` Linus Torvalds
2011-06-05  6:01                               ` Arne Jansen
2011-06-05  7:57                                 ` Mike Galbraith
2011-04-05 15:23 ` [PATCH 14/21] sched: Drop rq->lock from first part of wake_up_new_task() Peter Zijlstra
2011-04-14  8:37   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 15/21] sched: Drop rq->lock from sched_exec() Peter Zijlstra
2011-04-14  8:37   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 16/21] sched: Remove rq->lock from the first half of ttwu() Peter Zijlstra
2011-04-14  8:38   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 17/21] sched: Remove rq argument from ttwu_stat() Peter Zijlstra
2011-04-14  8:38   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 18/21] sched: Rename ttwu_post_activation Peter Zijlstra
2011-04-14  8:39   ` [tip:sched/locking] sched: Rename ttwu_post_activation() to ttwu_do_wakeup() tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 19/21] sched: Restructure ttwu some more Peter Zijlstra
2011-04-14  8:39   ` [tip:sched/locking] sched: Restructure ttwu() " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 20/21] sched: Move the second half of ttwu() to the remote cpu Peter Zijlstra
2011-04-14  8:39   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:23 ` [PATCH 21/21] sched: Remove need_migrate_task() Peter Zijlstra
2011-04-14  8:40   ` [tip:sched/locking] " tip-bot for Peter Zijlstra
2011-04-05 15:59 ` [PATCH 00/21] sched: Reduce runqueue lock contention -v6 Peter Zijlstra
2011-04-06 11:00 ` Peter Zijlstra
2011-04-27 16:54 ` Dave Kleikamp

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