Commit 2914b0ba authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

irq_work: Optimize irq_work_single() 



Trade one atomic op for a full memory barrier.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
parent 545b8c8d

include/linux/irqflags.h

+4 −4
Original line number Diff line number Diff line
@@ -107,14 +107,14 @@ do { \ 
		  current->irq_config = 0;			\

	  } while (0)



# define lockdep_irq_work_enter(__work)					\

# define lockdep_irq_work_enter(_flags)					\

	  do {								\

		  if (!(atomic_read(&__work->node.a_flags) & IRQ_WORK_HARD_IRQ))\

		  if (!((_flags) & IRQ_WORK_HARD_IRQ))			\

			current->irq_config = 1;			\

	  } while (0)

# define lockdep_irq_work_exit(__work)					\

# define lockdep_irq_work_exit(_flags)					\

	  do {								\

		  if (!(atomic_read(&__work->node.a_flags) & IRQ_WORK_HARD_IRQ))\

		  if (!((_flags) & IRQ_WORK_HARD_IRQ))			\

			current->irq_config = 0;			\

	  } while (0)

kernel/irq_work.c

+17 −12
Original line number Diff line number Diff line
@@ -34,7 +34,7 @@ static bool irq_work_claim(struct irq_work *work) 
	oflags = atomic_fetch_or(IRQ_WORK_CLAIMED | CSD_TYPE_IRQ_WORK, &work->node.a_flags);

	/*

	 * If the work is already pending, no need to raise the IPI.

	 * The pairing atomic_fetch_andnot() in irq_work_run() makes sure

	 * The pairing smp_mb() in irq_work_single() makes sure

	 * everything we did before is visible.

	 */

	if (oflags & IRQ_WORK_PENDING)
@@ -136,22 +136,27 @@ void irq_work_single(void *arg) 
	int flags;



	/*

	 * Clear the PENDING bit, after this point the @work

	 * can be re-used.

	 * Make it immediately visible so that other CPUs trying

	 * to claim that work don't rely on us to handle their data

	 * while we are in the middle of the func.

	 * Clear the PENDING bit, after this point the @work can be re-used.

	 * The PENDING bit acts as a lock, and we own it, so we can clear it

	 * without atomic ops.

	 */

	flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->node.a_flags);

	flags = atomic_read(&work->node.a_flags);

	flags &= ~IRQ_WORK_PENDING;

	atomic_set(&work->node.a_flags, flags);



	/*

	 * See irq_work_claim().

	 */

	smp_mb();



	lockdep_irq_work_enter(work);

	lockdep_irq_work_enter(flags);

	work->func(work);

	lockdep_irq_work_exit(work);

	lockdep_irq_work_exit(flags);



	/*

	 * Clear the BUSY bit and return to the free state if

	 * no-one else claimed it meanwhile.

	 * Clear the BUSY bit, if set, and return to the free state if no-one

	 * else claimed it meanwhile.

	 */

	flags &= ~IRQ_WORK_PENDING;

	(void)atomic_cmpxchg(&work->node.a_flags, flags, flags & ~IRQ_WORK_BUSY);

}