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io_uring: enable option to only trigger eventfd for async completions

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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: Mark Papadakis <markuspapadakis@icloud.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2020-01-08 11:04:00 -07:00
parent 69b3e54613
commit f2842ab5b7
2 changed files with 17 additions and 1 deletions
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17
fs/io_uring.c
View File

@ -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;

1
include/uapi/linux/io_uring.h
View File

@ -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;