From: Jens Axboe <axboe@suse.de>
To: "Jeff V. Merkey" <jmerkey@wolfmountaingroup.com>
Cc: Max Waterman <davidmaxwaterman+kernel@fastmail.co.uk>,
linux-kernel@vger.kernel.org
Subject: Re: io performance...
Date: Tue, 17 Jan 2006 14:57:31 +0100 [thread overview]
Message-ID: <20060117135731.GM3945@suse.de> (raw)
In-Reply-To: <43CB4C03.7070304@wolfmountaingroup.com>
On Mon, Jan 16 2006, Jeff V. Merkey wrote:
> Max Waterman wrote:
>
> >Hi,
> >
> >I've been referred to this list from the linux-raid list.
> >
> >I've been playing with a RAID system, trying to obtain best bandwidth
> >from it.
> >
> >I've noticed that I consistently get better (read) numbers from kernel
> >2.6.8
> >than from later kernels.
>
>
> To open the bottlenecks, the following works well. Jens will shoot me
> for recommending this,
> but it works well. 2.6.9 so far has the highest numbers with this fix.
> You can manually putz
> around with these numbers, but they are an artificial constraint if you
> are using RAID technology
> that caches ad elevators requests and consolidates them.
>
>
> Jeff
>
>
>
> diff -Naur ./include/linux/blkdev.h ../linux-2.6.9/./include/linux/blkdev.h
> --- ./include/linux/blkdev.h 2004-10-18 15:53:43.000000000 -0600
> +++ ../linux-2.6.9/./include/linux/blkdev.h 2005-12-06 09:54:46.000000000 -0700
> @@ -23,8 +23,10 @@
> typedef struct elevator_s elevator_t;
> struct request_pm_state;
>
> -#define BLKDEV_MIN_RQ 4
> -#define BLKDEV_MAX_RQ 128 /* Default maximum */
> +//#define BLKDEV_MIN_RQ 4
> +//#define BLKDEV_MAX_RQ 128 /* Default maximum */
> +#define BLKDEV_MIN_RQ 4096
> +#define BLKDEV_MAX_RQ 8192 /* Default maximum */
Yeah I could shoot you. However I'm more interested in why this is
necessary, eg I'd like to see some numbers from you comparing:
- The stock settings
- Doing
# echo 8192 > /sys/block/<dev>/queue/nr_requests
for each drive you are accessing.
- The kernel with your patch.
If #2 and #3 don't provide very similar profiles/scores, then we have
something to look at.
The BLKDEV_MIN_RQ increase is just silly and wastes a huge amount of
memory for no good reason.
--
Jens Axboe
next prev parent reply other threads:[~2006-01-17 13:55 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-16 7:35 io performance Max Waterman
2006-01-16 7:32 ` Jeff V. Merkey
2006-01-17 13:57 ` Jens Axboe [this message]
2006-01-17 19:17 ` Jeff V. Merkey
2006-01-16 8:35 ` Pekka Enberg
2006-01-17 17:06 ` Phillip Susi
2006-01-18 7:24 ` Max Waterman
2006-01-18 15:19 ` Phillip Susi
2006-01-20 5:58 ` Max Waterman
2006-01-20 13:42 ` Ian Soboroff
2006-01-25 6:36 ` Max Waterman
2006-01-25 14:19 ` Ian Soboroff
2006-01-25 13:09 ` Bernd Eckenfels
2006-01-18 3:02 ` Max Waterman
2006-01-18 4:30 ` Jeff V. Merkey
2006-01-18 5:09 ` Max Waterman
2006-01-18 4:37 ` Jeff V. Merkey
2006-01-18 7:06 ` Max Waterman
2006-01-18 9:21 ` Alan Cox
2006-01-18 15:48 ` Phillip Susi
2006-01-18 16:25 ` Bartlomiej Zolnierkiewicz
2006-01-19 0:48 ` Adrian Bunk
2006-01-19 13:18 ` Max Waterman
[not found] <5vx8f-1Al-21@gated-at.bofh.it>
[not found] ` <5wbRY-3cF-3@gated-at.bofh.it>
[not found] ` <5wdKh-5wF-15@gated-at.bofh.it>
2006-01-19 1:58 ` Robert Hancock
2006-01-19 13:14 ` Max Waterman
2006-01-19 14:08 ` Alan Cox
2006-01-20 4:09 ` Max Waterman
2006-01-20 4:27 ` Alexander Samad
2006-01-20 12:52 ` Alan Cox
2006-01-19 11:39 Al Boldi
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