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From: Pavel Begunkov <[email protected]>
To: [email protected]
Cc: Jens Axboe <[email protected]>, [email protected]
Subject: [PATCH 4/7] io_uring: remove extra barrier for non-sqpoll iopoll
Date: Thu, 17 Mar 2022 02:03:39 +0000	[thread overview]
Message-ID: <d72e8ef6f7a3f6a72e18fad8409f7d47afc8da7d.1647481208.git.asml.silence@gmail.com> (raw)
In-Reply-To: <[email protected]>

smp_mb() in io_cqring_ev_posted_iopoll() is only there because of
waitqueue_active(). However, non-SQPOLL IOPOLL ring doesn't wake the CQ
and so the barrier there is useless. Kill it, it's usually pretty
expensive.

Signed-off-by: Pavel Begunkov <[email protected]>
---
 fs/io_uring.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index bbbbf889dfd8..603cbe687dd2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1869,11 +1869,8 @@ static void io_cqring_ev_posted(struct io_ring_ctx *ctx)
 
 static void io_cqring_ev_posted_iopoll(struct io_ring_ctx *ctx)
 {
-	/* see waitqueue_active() comment */
-	smp_mb();
-
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
-		if (waitqueue_active(&ctx->cq_wait))
+		if (wq_has_sleeper(&ctx->cq_wait))
 			wake_up_all(&ctx->cq_wait);
 	}
 	io_eventfd_signal(ctx);
-- 
2.35.1


  parent reply	other threads:[~2022-03-17  2:05 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-17  2:03 [PATCH for-next 0/7] completion path optimisations Pavel Begunkov
2022-03-17  2:03 ` [PATCH 1/7] io_uring: normilise naming for fill_cqe* Pavel Begunkov
2022-03-17  2:03 ` [PATCH 2/7] io_uring: refactor timeout cancellation cqe posting Pavel Begunkov
2022-03-17  2:03 ` [PATCH 3/7] io_uring: extend provided buf return to fails Pavel Begunkov
2022-03-17  2:14   ` Jens Axboe
2022-03-17  2:03 ` Pavel Begunkov [this message]
2022-03-17  2:03 ` [PATCH 5/7] io_uring: shuffle io_eventfd_signal() bits around Pavel Begunkov
2022-03-17  2:03 ` [PATCH 6/7] io_uring: thin down io_commit_cqring() Pavel Begunkov
2022-03-17  2:03 ` [PATCH 7/7] io_uring: fold evfd signalling under a slower path Pavel Begunkov
2022-03-17 12:31 ` [PATCH for-next 0/7] completion path optimisations Jens Axboe

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