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

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  [PATCH] noop-iosched: do not attempt to sort requests Tahsin Erdogan <tahsin@google.com> - 2015-07-23 23:30 +0200
    Re: [PATCH] noop-iosched: do not attempt to sort requests Tahsin Erdogan <tahsin@google.com> - 2015-07-30 07:50 +0200

#1191328 — [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@google.com>
Signed-off-by: Tahsin Erdogan <tahsin@google.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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#1195720

Hi Jens, did you get a chance to take a look at this patch?

On Thu, Jul 23, 2015 at 2:20 PM, Tahsin Erdogan <tahsin@google.com> wrote:
> 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@google.com>
> Signed-off-by: Tahsin Erdogan <tahsin@google.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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