From 0f84747177b962c32243a57cb454193bdba4fe8d Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Thu, 17 Mar 2022 02:03:39 +0000
Subject: [PATCH] io_uring: remove extra barrier for non-sqpoll iopoll
Git-commit: 0f84747177b962c32243a57cb454193bdba4fe8d
Patch-mainline: v5.18-rc1
References: bsc#1205205
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 <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/d72e8ef6f7a3f6a72e18fad8409f7d47afc8da7d.1647481208.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
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 f039706bce0e..692dbe7b98e9 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1877,11 +1877,8 @@ 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);
--
2.35.3