Commit f2842ab5 authored by Jens Axboe's avatar Jens Axboe
Browse files

io_uring: enable option to only trigger eventfd for async completions 



If an application is using eventfd notifications with poll to know when
new SQEs can be issued, it's expecting the following read/writes to
complete inline. And with that, it knows that there are events available,
and don't want spurious wakeups on the eventfd for those requests.

This adds IORING_REGISTER_EVENTFD_ASYNC, which works just like
IORING_REGISTER_EVENTFD, except it only triggers notifications for events
that happen from async completions (IRQ, or io-wq worker completions).
Any completions inline from the submission itself will not trigger
notifications.

Suggested-by: default avatarMark Papadakis <markuspapadakis@icloud.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 69b3e546

fs/io_uring.c

+16 −1
Original line number Diff line number Diff line
@@ -206,6 +206,7 @@ struct io_ring_ctx { 
		int			account_mem: 1;

		int			cq_overflow_flushed: 1;

		int			drain_next: 1;

		int			eventfd_async: 1;



		/*

		 * Ring buffer of indices into array of io_uring_sqe, which is
@@ -963,13 +964,20 @@ static struct io_uring_cqe *io_get_cqring(struct io_ring_ctx *ctx) 
	return &rings->cqes[tail & ctx->cq_mask];

}



static inline bool io_should_trigger_evfd(struct io_ring_ctx *ctx)

{

	if (!ctx->eventfd_async)

		return true;

	return io_wq_current_is_worker() || in_interrupt();

}



static void io_cqring_ev_posted(struct io_ring_ctx *ctx)

{

	if (waitqueue_active(&ctx->wait))

		wake_up(&ctx->wait);

	if (waitqueue_active(&ctx->sqo_wait))

		wake_up(&ctx->sqo_wait);

	if (ctx->cq_ev_fd)

	if (ctx->cq_ev_fd && io_should_trigger_evfd(ctx))

		eventfd_signal(ctx->cq_ev_fd, 1);

}
@@ -6556,10 +6564,17 @@ static int __io_uring_register(struct io_ring_ctx *ctx, unsigned opcode, 
		ret = io_sqe_files_update(ctx, arg, nr_args);

		break;

	case IORING_REGISTER_EVENTFD:

	case IORING_REGISTER_EVENTFD_ASYNC:

		ret = -EINVAL;

		if (nr_args != 1)

			break;

		ret = io_eventfd_register(ctx, arg);

		if (ret)

			break;

		if (opcode == IORING_REGISTER_EVENTFD_ASYNC)

			ctx->eventfd_async = 1;

		else

			ctx->eventfd_async = 0;

		break;

	case IORING_UNREGISTER_EVENTFD:

		ret = -EINVAL;

include/uapi/linux/io_uring.h

+1 −0
Original line number Diff line number Diff line
@@ -192,6 +192,7 @@ struct io_uring_params { 
#define IORING_REGISTER_EVENTFD		4

#define IORING_UNREGISTER_EVENTFD	5

#define IORING_REGISTER_FILES_UPDATE	6

#define IORING_REGISTER_EVENTFD_ASYNC	7



struct io_uring_files_update {

	__u32 offset;

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