linux-kernel - [PATCH] noop-iosched: do not attempt to sort requests

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Message-Id: <1437686414-19941-1-git-send-email-tahsin@google.com>
Date:	Thu, 23 Jul 2015 14:20:14 -0700
From:	Tahsin Erdogan <tahsin@...gle.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org, nauman@...gle.com, tytso@....edu,
	Tahsin Erdogan <tahsin@...gle.com>
Subject: [PATCH] noop-iosched: do not attempt to sort requests

Noop scheduler currently dispatches a request by calling
elv_dispatch_sort(). In practice, sorting does not occur because
__elv_next_request() asks the io scheduler to dispatch a request
only when elevator queue is empty.

Also, not reordering requests seems more appropriate for noop. This
change makes the behavior more explicit.

Reviewed-by: Nauman Rafique <nauman@...gle.com>
Signed-off-by: Tahsin Erdogan <tahsin@...gle.com>
---
 block/Kconfig.iosched | 8 ++++----
 block/noop-iosched.c  | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/block/Kconfig.iosched b/block/Kconfig.iosched
index 421bef9..b9e42f8 100644
--- a/block/Kconfig.iosched
+++ b/block/Kconfig.iosched
@@ -7,10 +7,10 @@ config IOSCHED_NOOP
 	default y
 	---help---
 	  The no-op I/O scheduler is a minimal scheduler that does basic merging
-	  and sorting. Its main uses include non-disk based block devices like
-	  memory devices, and specialised software or hardware environments
-	  that do their own scheduling and require only minimal assistance from
-	  the kernel.
+	  only. Its main uses include non-disk based block devices like memory
+	  devices, and specialised software or hardware environments that do
+	  their own scheduling and require only minimal assistance from the
+	  kernel.
 
 config IOSCHED_DEADLINE
 	tristate "Deadline I/O scheduler"
diff --git a/block/noop-iosched.c b/block/noop-iosched.c
index 3de89d4..f0fec14 100644
--- a/block/noop-iosched.c
+++ b/block/noop-iosched.c
@@ -26,7 +26,7 @@ static int noop_dispatch(struct request_queue *q, int force)
 		struct request *rq;
 		rq = list_entry(nd->queue.next, struct request, queuelist);
 		list_del_init(&rq->queuelist);
-		elv_dispatch_sort(q, rq);
+		elv_dispatch_add_tail(q, rq);
 		return 1;
 	}
 	return 0;
-- 
2.4.3.573.g4eafbef

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