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Commit d269a8b8 authored by Davidlohr Bueso's avatar Davidlohr Bueso Committed by Ingo Molnar
Browse files

kernel/locking: Compute 'current' directly 



This patch effectively replaces the tsk pointer dereference
(which is obviously == current), to directly use get_current()
macro. This is to make the removal of setting foreign task
states smoother and painfully obvious. Performance win on some
archs such as x86-64 and ppc64. On a microbenchmark that calls
set_task_state() vs set_current_state() and an inode rwsem
pounding benchmark doing unlink:

== 1. x86-64 ==

Avg runtime set_task_state():    601 msecs
Avg runtime set_current_state(): 552 msecs

                                            vanilla                 dirty
Hmean    unlink1-processes-2      36089.26 (  0.00%)    38977.33 (  8.00%)
Hmean    unlink1-processes-5      28555.01 (  0.00%)    29832.55 (  4.28%)
Hmean    unlink1-processes-8      37323.75 (  0.00%)    44974.57 ( 20.50%)
Hmean    unlink1-processes-12     43571.88 (  0.00%)    44283.01 (  1.63%)
Hmean    unlink1-processes-21     34431.52 (  0.00%)    38284.45 ( 11.19%)
Hmean    unlink1-processes-30     34813.26 (  0.00%)    37975.17 (  9.08%)
Hmean    unlink1-processes-48     37048.90 (  0.00%)    39862.78 (  7.59%)
Hmean    unlink1-processes-79     35630.01 (  0.00%)    36855.30 (  3.44%)
Hmean    unlink1-processes-110    36115.85 (  0.00%)    39843.91 ( 10.32%)
Hmean    unlink1-processes-141    32546.96 (  0.00%)    35418.52 (  8.82%)
Hmean    unlink1-processes-172    34674.79 (  0.00%)    36899.21 (  6.42%)
Hmean    unlink1-processes-203    37303.11 (  0.00%)    36393.04 ( -2.44%)
Hmean    unlink1-processes-224    35712.13 (  0.00%)    36685.96 (  2.73%)

== 2. ppc64le ==

Avg runtime set_task_state():  938 msecs
Avg runtime set_current_state: 940 msecs

                                            vanilla                 dirty
Hmean    unlink1-processes-2      19269.19 (  0.00%)    30704.50 ( 59.35%)
Hmean    unlink1-processes-5      20106.15 (  0.00%)    21804.15 (  8.45%)
Hmean    unlink1-processes-8      17496.97 (  0.00%)    17243.28 ( -1.45%)
Hmean    unlink1-processes-12     14224.15 (  0.00%)    17240.21 ( 21.20%)
Hmean    unlink1-processes-21     14155.66 (  0.00%)    15681.23 ( 10.78%)
Hmean    unlink1-processes-30     14450.70 (  0.00%)    15995.83 ( 10.69%)
Hmean    unlink1-processes-48     16945.57 (  0.00%)    16370.42 ( -3.39%)
Hmean    unlink1-processes-79     15788.39 (  0.00%)    14639.27 ( -7.28%)
Hmean    unlink1-processes-110    14268.48 (  0.00%)    14377.40 (  0.76%)
Hmean    unlink1-processes-141    14023.65 (  0.00%)    16271.69 ( 16.03%)
Hmean    unlink1-processes-172    13417.62 (  0.00%)    16067.55 ( 19.75%)
Hmean    unlink1-processes-203    15293.08 (  0.00%)    15440.40 (  0.96%)
Hmean    unlink1-processes-234    13719.32 (  0.00%)    16190.74 ( 18.01%)
Hmean    unlink1-processes-265    16400.97 (  0.00%)    16115.22 ( -1.74%)
Hmean    unlink1-processes-296    14388.60 (  0.00%)    16216.13 ( 12.70%)
Hmean    unlink1-processes-320    15771.85 (  0.00%)    15905.96 (  0.85%)

Signed-off-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Cc: mark.rutland@arm.com
Link: http://lkml.kernel.org/r/1483479794-14013-4-git-send-email-dave@stgolabs.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 5376f2e7

kernel/locking/mutex.c

+9 −10
Original line number Diff line number Diff line
@@ -622,7 +622,6 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
		    struct lockdep_map *nest_lock, unsigned long ip,

		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)

{

	struct task_struct *task = current;

	struct mutex_waiter waiter;

	unsigned long flags;

	bool first = false;
@@ -656,18 +655,18 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
		goto skip_wait;



	debug_mutex_lock_common(lock, &waiter);

	debug_mutex_add_waiter(lock, &waiter, task);

	debug_mutex_add_waiter(lock, &waiter, current);



	/* add waiting tasks to the end of the waitqueue (FIFO): */

	list_add_tail(&waiter.list, &lock->wait_list);

	waiter.task = task;

	waiter.task = current;



	if (__mutex_waiter_is_first(lock, &waiter))

		__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);



	lock_contended(&lock->dep_map, ip);



	set_task_state(task, state);

	set_task_state(current, state);

	for (;;) {

		/*

		 * Once we hold wait_lock, we're serialized against
@@ -683,7 +682,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
		 * wait_lock. This ensures the lock cancellation is ordered

		 * against mutex_unlock() and wake-ups do not go missing.

		 */

		if (unlikely(signal_pending_state(state, task))) {

		if (unlikely(signal_pending_state(state, current))) {

			ret = -EINTR;

			goto err;

		}
@@ -702,7 +701,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
			__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);

		}



		set_task_state(task, state);

		set_task_state(current, state);

		/*

		 * Here we order against unlock; we must either see it change

		 * state back to RUNNING and fall through the next schedule(),
@@ -716,9 +715,9 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
	}

	spin_lock_mutex(&lock->wait_lock, flags);

acquired:

	__set_task_state(task, TASK_RUNNING);

	__set_task_state(current, TASK_RUNNING);



	mutex_remove_waiter(lock, &waiter, task);

	mutex_remove_waiter(lock, &waiter, current);

	if (likely(list_empty(&lock->wait_list)))

		__mutex_clear_flag(lock, MUTEX_FLAGS);
@@ -736,8 +735,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, 
	return 0;



err:

	__set_task_state(task, TASK_RUNNING);

	mutex_remove_waiter(lock, &waiter, task);

	__set_task_state(current, TASK_RUNNING);

	mutex_remove_waiter(lock, &waiter, current);

	spin_unlock_mutex(&lock->wait_lock, flags);

	debug_mutex_free_waiter(&waiter);

	mutex_release(&lock->dep_map, 1, ip);

kernel/locking/rwsem-spinlock.c

+7 −11
Original line number Diff line number Diff line
@@ -128,7 +128,6 @@ __rwsem_wake_one_writer(struct rw_semaphore *sem) 
void __sched __down_read(struct rw_semaphore *sem)

{

	struct rwsem_waiter waiter;

	struct task_struct *tsk;

	unsigned long flags;



	raw_spin_lock_irqsave(&sem->wait_lock, flags);
@@ -140,13 +139,12 @@ void __sched __down_read(struct rw_semaphore *sem) 
		goto out;

	}



	tsk = current;

	set_task_state(tsk, TASK_UNINTERRUPTIBLE);

	set_task_state(current, TASK_UNINTERRUPTIBLE);



	/* set up my own style of waitqueue */

	waiter.task = tsk;

	waiter.task = current;

	waiter.type = RWSEM_WAITING_FOR_READ;

	get_task_struct(tsk);

	get_task_struct(current);



	list_add_tail(&waiter.list, &sem->wait_list);
@@ -158,10 +156,10 @@ void __sched __down_read(struct rw_semaphore *sem) 
		if (!waiter.task)

			break;

		schedule();

		set_task_state(tsk, TASK_UNINTERRUPTIBLE);

		set_task_state(current, TASK_UNINTERRUPTIBLE);

	}



	__set_task_state(tsk, TASK_RUNNING);

	__set_task_state(current, TASK_RUNNING);

 out:

	;

}
@@ -194,15 +192,13 @@ int __down_read_trylock(struct rw_semaphore *sem) 
int __sched __down_write_common(struct rw_semaphore *sem, int state)

{

	struct rwsem_waiter waiter;

	struct task_struct *tsk;

	unsigned long flags;

	int ret = 0;



	raw_spin_lock_irqsave(&sem->wait_lock, flags);



	/* set up my own style of waitqueue */

	tsk = current;

	waiter.task = tsk;

	waiter.task = current;

	waiter.type = RWSEM_WAITING_FOR_WRITE;

	list_add_tail(&waiter.list, &sem->wait_list);
@@ -220,7 +216,7 @@ int __sched __down_write_common(struct rw_semaphore *sem, int state) 
			ret = -EINTR;

			goto out;

		}

		set_task_state(tsk, state);

		set_task_state(current, state);

		raw_spin_unlock_irqrestore(&sem->wait_lock, flags);

		schedule();

		raw_spin_lock_irqsave(&sem->wait_lock, flags);

kernel/locking/rwsem-xadd.c

+3 −4
Original line number Diff line number Diff line
@@ -224,10 +224,9 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) 
{

	long count, adjustment = -RWSEM_ACTIVE_READ_BIAS;

	struct rwsem_waiter waiter;

	struct task_struct *tsk = current;

	DEFINE_WAKE_Q(wake_q);



	waiter.task = tsk;

	waiter.task = current;

	waiter.type = RWSEM_WAITING_FOR_READ;



	raw_spin_lock_irq(&sem->wait_lock);
@@ -254,13 +253,13 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) 


	/* wait to be given the lock */

	while (true) {

		set_task_state(tsk, TASK_UNINTERRUPTIBLE);

		set_task_state(current, TASK_UNINTERRUPTIBLE);

		if (!waiter.task)

			break;

		schedule();

	}



	__set_task_state(tsk, TASK_RUNNING);

	__set_task_state(current, TASK_RUNNING);

	return sem;

}

EXPORT_SYMBOL(rwsem_down_read_failed);

kernel/locking/semaphore.c

+3 −4
Original line number Diff line number Diff line
@@ -204,19 +204,18 @@ struct semaphore_waiter { 
static inline int __sched __down_common(struct semaphore *sem, long state,

								long timeout)

{

	struct task_struct *task = current;

	struct semaphore_waiter waiter;



	list_add_tail(&waiter.list, &sem->wait_list);

	waiter.task = task;

	waiter.task = current;

	waiter.up = false;



	for (;;) {

		if (signal_pending_state(state, task))

		if (signal_pending_state(state, current))

			goto interrupted;

		if (unlikely(timeout <= 0))

			goto timed_out;

		__set_task_state(task, state);

		__set_task_state(current, state);

		raw_spin_unlock_irq(&sem->lock);

		timeout = schedule_timeout(timeout);

		raw_spin_lock_irq(&sem->lock);