linux-kernel - [PATCH] rbd: optimize barrier usage for Rmw atomic bitops

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Date:   Wed, 29 Jan 2020 10:12:53 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     idryomov@...il.com
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        dave@...olabs.net, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH] rbd: optimize barrier usage for Rmw atomic bitops

For both set and clear_bit, we can avoid the unnecessary barrier
on non LL/SC architectures, such as x86. Instead, use the
smp_mb__{before,after}_atomic() calls.

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 drivers/block/rbd.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 2b184563cd32..7bc79b2b8f65 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1371,13 +1371,13 @@ static void rbd_osd_submit(struct ceph_osd_request *osd_req)
 static void img_request_layered_set(struct rbd_img_request *img_request)
 {
 	set_bit(IMG_REQ_LAYERED, &img_request->flags);
-	smp_mb();
+	smp_mb__after_atomic();
 }
 
 static void img_request_layered_clear(struct rbd_img_request *img_request)
 {
 	clear_bit(IMG_REQ_LAYERED, &img_request->flags);
-	smp_mb();
+	smp_mb__after_atomic();
 }
 
 static bool img_request_layered_test(struct rbd_img_request *img_request)
-- 
2.16.4