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io_uring: combine cq_wait_nr checks 

Instead of explicitly checking ->cq_wait_nr for whether there are
waiting, which is currently represented by 0, we can store there a
large value and the nr_tw will automatically filter out those cases.
Add a named constant for that and for the wake up bias value.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/38def30282654d980673976cd42fde9bab19b297.1705438669.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2024-01-17 00:57:29 +00:00 committed by Jens Axboe
parent e8c407717b
commit b4bc35cf87
1 changed files with 27 additions and 7 deletions
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34
io_uring/io_uring.c
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@ -137,6 +137,14 @@ struct io_defer_entry {
#define IO_DISARM_MASK (REQ_F_ARM_LTIMEOUT | REQ_F_LINK_TIMEOUT | REQ_F_FAIL)
#define IO_REQ_LINK_FLAGS (REQ_F_LINK | REQ_F_HARDLINK)
/*
* No waiters. It's larger than any valid value of the tw counter
* so that tests against ->cq_wait_nr would fail and skip wake_up().
*/
#define IO_CQ_WAKE_INIT (-1U)
/* Forced wake up if there is a waiter regardless of ->cq_wait_nr */
#define IO_CQ_WAKE_FORCE (IO_CQ_WAKE_INIT >> 1)
static bool io_uring_try_cancel_requests(struct io_ring_ctx *ctx,
struct task_struct *task,
bool cancel_all);
@ -303,6 +311,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
goto err;
ctx->flags = p->flags;
atomic_set(&ctx->cq_wait_nr, IO_CQ_WAKE_INIT);
init_waitqueue_head(&ctx->sqo_sq_wait);
INIT_LIST_HEAD(&ctx->sqd_list);
INIT_LIST_HEAD(&ctx->cq_overflow_list);
@ -1306,6 +1315,13 @@ static inline void io_req_local_work_add(struct io_kiocb *req, unsigned flags)
unsigned nr_wait, nr_tw, nr_tw_prev;
struct llist_node *head;
/* See comment above IO_CQ_WAKE_INIT */
BUILD_BUG_ON(IO_CQ_WAKE_FORCE <= IORING_MAX_CQ_ENTRIES);
/*
* We don't know how many reuqests is there in the link and whether
* they can even be queued lazily, fall back to non-lazy.
*/
if (req->flags & (REQ_F_LINK | REQ_F_HARDLINK))
flags &= ~IOU_F_TWQ_LAZY_WAKE;
@ -1322,10 +1338,14 @@ static inline void io_req_local_work_add(struct io_kiocb *req, unsigned flags)
*/
nr_tw_prev = READ_ONCE(first_req->nr_tw);
}
/*
* Theoretically, it can overflow, but that's fine as one of
* previous adds should've tried to wake the task.
*/
nr_tw = nr_tw_prev + 1;
/* Large enough to fail the nr_wait comparison below */
if (!(flags & IOU_F_TWQ_LAZY_WAKE))
nr_tw = INT_MAX;
nr_tw = IO_CQ_WAKE_FORCE;
req->nr_tw = nr_tw;
req->io_task_work.node.next = head;
@ -1348,11 +1368,11 @@ static inline void io_req_local_work_add(struct io_kiocb *req, unsigned flags)
}
nr_wait = atomic_read(&ctx->cq_wait_nr);
/* no one is waiting */
if (!nr_wait)
/* not enough or no one is waiting */
if (nr_tw < nr_wait)
return;
/* either not enough or the previous add has already woken it up */
if (nr_wait > nr_tw || nr_tw_prev >= nr_wait)
/* the previous add has already woken it up */
if (nr_tw_prev >= nr_wait)
return;
wake_up_state(ctx->submitter_task, TASK_INTERRUPTIBLE);
}
@ -2620,7 +2640,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
ret = io_cqring_wait_schedule(ctx, &iowq);
__set_current_state(TASK_RUNNING);
atomic_set(&ctx->cq_wait_nr, 0);
atomic_set(&ctx->cq_wait_nr, IO_CQ_WAKE_INIT);
/*
* Run task_work after scheduling and before io_should_wake().