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

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Message-ID: <CAAeU0aOAUYPv=OAKYs9VFXCj-Xh+-Jd=WD-KNsK-pkZXSiM-tw@mail.gmail.com>
Date:	Wed, 29 Jul 2015 22:49:16 -0700
From:	Tahsin Erdogan <tahsin@...gle.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org, Nauman Rafique <nauman@...gle.com>,
	"Theodore Ts'o" <tytso@....edu>, Tahsin Erdogan <tahsin@...gle.com>
Subject: Re: [PATCH] noop-iosched: do not attempt to sort requests

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@...gle.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@...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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