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io_uring: wake up optimisations 

Flush completions is done either from the submit syscall or by the
task_work, both are in the context of the submitter task, and when it
goes for a single threaded rings like implied by ->task_complete, there
won't be any waiters on ->cq_wait but the master task. That means that
there can be no tasks sleeping on cq_wait while we run
__io_submit_flush_completions() and so waking up can be skipped.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/60ad9768ec74435a0ddaa6eec0ffa7729474f69f.1673274244.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2023-01-09 14:46:10 +00:00 committed by Jens Axboe
parent bca39f3905
commit 3181e22fb7
1 changed files with 20 additions and 1 deletions
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21
io_uring/io_uring.c
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@ -621,6 +621,25 @@ static inline void __io_cq_unlock_post(struct io_ring_ctx *ctx)
io_cqring_wake(ctx);
}
static inline void __io_cq_unlock_post_flush(struct io_ring_ctx *ctx)
__releases(ctx->completion_lock)
{
io_commit_cqring(ctx);
__io_cq_unlock(ctx);
io_commit_cqring_flush(ctx);
/*
* As ->task_complete implies that the ring is single tasked, cq_wait
* may only be waited on by the current in io_cqring_wait(), but since
* it will re-check the wakeup conditions once we return we can safely
* skip waking it up.
*/
if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN)) {
smp_mb();
__io_cqring_wake(ctx);
}
}
void io_cq_unlock_post(struct io_ring_ctx *ctx)
__releases(ctx->completion_lock)
{
@ -1480,7 +1499,7 @@ static void __io_submit_flush_completions(struct io_ring_ctx *ctx)
}
}
}
__io_cq_unlock_post(ctx);
__io_cq_unlock_post_flush(ctx);
if (!wq_list_empty(&ctx->submit_state.compl_reqs)) {
io_free_batch_list(ctx, state->compl_reqs.first);