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From:   Yu Kuai <yukuai1@huaweicloud.com>
To:     aligrudi@gmail.com, song@kernel.org
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yukuai3@huawei.com, yukuai1@huaweicloud.com, yi.zhang@huawei.com,
        yangerkun@huawei.com
Subject: [PATCH] raid10: avoid spin_lock from fastpath from raid10_unplug()
Date:   Sun, 18 Jun 2023 22:25:20 +0800
Message-Id: <20230618142520.14662-1-yukuai1@huaweicloud.com>
MIME-Version: 1.0
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From: Yu Kuai <yukuai3@huawei.com>

Commit 0c0be98bbe67 ("md/raid10: prevent unnecessary calls to wake_up()
in fast path") missed one place, for example, while testing with:

fio -direct=1 -rw=write/randwrite -iodepth=1 ...

Then plug and unplug will be called for each io, then wake_up() from
raid10_unplug() will cause lock contention as well.

Avoid this contention by using wake_up_barrier() instead of wake_up(),
where spin_lock is not held while waitqueue is empty.

By the way, in this scenario, each blk_plug_cb() will be allocated and
freed for each io, this seems need to be optimized as well.

Reported-and-tested-by: Ali Gholami Rudi <aligrudi@gmail.com>
Link: https://lore.kernel.org/all/20231606122233@laper.mirepesht/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/raid10.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index d0de8c9fb3cf..fbaaa5e05edc 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1118,7 +1118,7 @@ static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)
 		spin_lock_irq(&conf->device_lock);
 		bio_list_merge(&conf->pending_bio_list, &plug->pending);
 		spin_unlock_irq(&conf->device_lock);
-		wake_up(&conf->wait_barrier);
+		wake_up_barrier(conf);
 		md_wakeup_thread(mddev->thread);
 		kfree(plug);
 		return;
@@ -1127,7 +1127,7 @@ static void raid10_unplug(struct blk_plug_cb *cb, bool from_schedule)
 	/* we aren't scheduling, so we can do the write-out directly. */
 	bio = bio_list_get(&plug->pending);
 	raid1_prepare_flush_writes(mddev->bitmap);
-	wake_up(&conf->wait_barrier);
+	wake_up_barrier(conf);
 
 	while (bio) { /* submit pending writes */
 		struct bio *next = bio->bi_next;
-- 
2.39.2