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irq_work: Optimize irq_work_single()

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Trade one atomic op for a full memory barrier.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
This commit is contained in:
Peter Zijlstra 2020-06-18 22:28:37 +02:00
parent 545b8c8df4
commit 2914b0ba61
2 changed files with 24 additions and 19 deletions
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8
include/linux/irqflags.h
View File

@ -107,14 +107,14 @@ do { \
current->irq_config = 0; \ current->irq_config = 0; \
} while (0) } while (0)
# define lockdep_irq_work_enter(__work) \ # define lockdep_irq_work_enter(_flags) \
do { \ do { \
if (!(atomic_read(&__work->node.a_flags) & IRQ_WORK_HARD_IRQ))\ if (!((_flags) & IRQ_WORK_HARD_IRQ)) \
current->irq_config = 1; \ current->irq_config = 1; \
} while (0) } while (0)
# define lockdep_irq_work_exit(__work) \ # define lockdep_irq_work_exit(_flags) \
do { \ do { \
if (!(atomic_read(&__work->node.a_flags) & IRQ_WORK_HARD_IRQ))\ if (!((_flags) & IRQ_WORK_HARD_IRQ)) \
current->irq_config = 0; \ current->irq_config = 0; \
} while (0) } while (0)

35
kernel/irq_work.c
View File

@ -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); 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. * 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. * everything we did before is visible.
*/ */
if (oflags & IRQ_WORK_PENDING) if (oflags & IRQ_WORK_PENDING)
@ -136,22 +136,27 @@ void irq_work_single(void *arg)
int flags; int flags;
/* /*
* Clear the PENDING bit, after this point the @work * Clear the PENDING bit, after this point the @work can be re-used.
* can be re-used. * The PENDING bit acts as a lock, and we own it, so we can clear it
* Make it immediately visible so that other CPUs trying * without atomic ops.
* to claim that work don't rely on us to handle their data
* while we are in the middle of the func.
*/
flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->node.a_flags);
lockdep_irq_work_enter(work);
work->func(work);
lockdep_irq_work_exit(work);
/*
* Clear the BUSY bit and return to the free state if
* no-one else claimed it meanwhile.
*/ */
flags = atomic_read(&work->node.a_flags);
flags &= ~IRQ_WORK_PENDING; flags &= ~IRQ_WORK_PENDING;
atomic_set(&work->node.a_flags, flags);
/*
* See irq_work_claim().
*/
smp_mb();
lockdep_irq_work_enter(flags);
work->func(work);
lockdep_irq_work_exit(flags);
/*
* Clear the BUSY bit, if set, and return to the free state if no-one
* else claimed it meanwhile.
*/
(void)atomic_cmpxchg(&work->node.a_flags, flags, flags & ~IRQ_WORK_BUSY); (void)atomic_cmpxchg(&work->node.a_flags, flags, flags & ~IRQ_WORK_BUSY);
} }