linux-kernel - Re: [PATCH -mm] [2/2] Add the Elevator I/O scheduler

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Date:	Fri, 4 Aug 2006 01:55:56 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Nate Diller <nate.diller@...il.com>
Cc:	Andrew Morton <akpm@...l.org>, Jens Axboe <axboe@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -mm] [2/2] Add the Elevator I/O scheduler

On Thu, Aug 03, 2006 at 04:03:19PM -0700, Nate Diller wrote:
>...
> Tested and benchmarked extensively on several platforms with several
> disk controllers and multiple brands of disk.  Subsequently ported
> forward from 2.6.14, compile and boot tested on 2.6.18-rc1-mm2.
>...
> --- linux-2.6.18-rc1-mm2/block/Kconfig.iosched	2006-07-18
> 14:52:29.000000000 -0700
> +++ linux-dput/block/Kconfig.iosched	2006-08-02 17:40:01.000000000 -0700
>...
> +config IOSCHED_EL_SSTF
> +	bool "Alternate Heuristic: Shortest Seek Time First" if 
> IOSCHED_ELEVATOR
> +	default n
> +	---help---
> +	  Elevator normally uses the C-SCAN one-way elevator algorithm,
> +	  which is useful in most situations to avoid queue congestion and
> +	  request starvation.  In some cases, SSTF might be higher
> +	  performance, particularly with certain localized workloads.
> +
> +	  If you don't know that you want this, you don't.

If you want to make your scheduler tunable, this should be a run-time 
option.

>...
> choice
> 	prompt "Default I/O scheduler"
> -	default DEFAULT_CFQ
> +	default DEFAULT_AS
> 	help
> 	  Select the I/O scheduler which will be used by default for all
> 	  block devices.
> 
> 	config DEFAULT_AS
> -		bool "Anticipatory" if IOSCHED_AS=y
> +		bool "Anticipatory" if IOSCHED_AS
> 
> 	config DEFAULT_DEADLINE
> -		bool "Deadline" if IOSCHED_DEADLINE=y
> +		bool "Deadline" if IOSCHED_DEADLINE
> 
> 	config DEFAULT_CFQ
> -		bool "CFQ" if IOSCHED_CFQ=y
> +		bool "CFQ" if IOSCHED_CFQ
> +
> +	config DEFAULT_ELEVATOR
> +		bool "Elevator" if IOSCHED_ELEVATOR
> 
> 	config DEFAULT_NOOP
> 		bool "No-op"
>...

It seems something went wrong when you forward ported your patch.
 
> --- linux-2.6.18-rc1-mm2/block/ll_rw_blk.c	2006-07-18 
> 15:00:44.000000000 -0700
> +++ linux-dput/block/ll_rw_blk.c	2006-08-01 13:56:34.000000000 -0700
>...
> @@ -2951,7 +2953,7 @@ get_rq:
> 		blk_plug_device(q);
> 	add_request(q, req);
> out:
> -	if (sync)
> +/*	if (sync)*/
> 		__generic_unplug_device(q);
> 
> 	spin_unlock_irq(q->queue_lock);
>...

Why?


cu
Adrian

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