linux-kernel - [PATCH V2 5/7] loop: improve loop_process

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Date:   Wed, 28 Jul 2021 16:16:36 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Dan Schatzberg <schatzberg.dan@...il.com>,
        Ming Lei <ming.lei@...hat.com>
Subject: [PATCH V2 5/7] loop: improve loop_process_work

Avoid to acquire the spinlock for handling every loop command, and hold
lock once for taking all commands.

Acked-by: Dan Schatzberg <schatzberg.dan@...il.com>
Signed-off-by: Ming Lei <ming.lei@...hat.com>
---
 drivers/block/loop.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 4c524c72d976..74682c0f3f86 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2174,21 +2174,26 @@ static void loop_process_work(struct loop_worker *worker,
 {
 	int orig_flags = current->flags;
 	struct loop_cmd *cmd;
+	LIST_HEAD(list);
 
 	current->flags |= PF_LOCAL_THROTTLE | PF_MEMALLOC_NOIO;
+
 	spin_lock(&lo->lo_work_lock);
-	while (!list_empty(cmd_list)) {
-		cmd = container_of(
-			cmd_list->next, struct loop_cmd, list_entry);
-		list_del(cmd_list->next);
-		spin_unlock(&lo->lo_work_lock);
+ again:
+	list_splice_init(cmd_list, &list);
+	spin_unlock(&lo->lo_work_lock);
 
-		loop_handle_cmd(cmd);
-		cond_resched();
+	while (!list_empty(&list)) {
+		cmd = list_first_entry(&list, struct loop_cmd, list_entry);
+		list_del_init(&cmd->list_entry);
 
-		spin_lock(&lo->lo_work_lock);
+		loop_handle_cmd(cmd);
 	}
 
+	spin_lock(&lo->lo_work_lock);
+	if (!list_empty(cmd_list))
+		goto again;
+
 	/*
 	 * We only add to the idle list if there are no pending cmds
 	 * *and* the worker will not run again which ensures that it
-- 
2.31.1