From: Marc-Christian Petersen <m.c.p@wolk-project.de>
Organization: Working Overloaded Linux Kernel
To: Andrea Arcangeli <andrea@suse.de>
Subject: Re: 2.4.22pre6aa1
Date: Tue, 22 Jul 2003 15:34:16 +0200
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Cc: linux-kernel@vger.kernel.org, Chris Mason <mason@suse.com>
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On Friday 18 July 2003 00:50, Andrea Arcangeli wrote:

Hi Andrea,

> Can you try to change include/linux/blkdev.h like this:
> -#define MAX_QUEUE_SECTORS (4 << (20 - 9)) /* 4 mbytes when full sized */
> +#define MAX_QUEUE_SECTORS (16 << (20 - 9)) /* 4 mbytes when full sized */
> This will raise the queue from 4 to 16M. That is the first(/only) thing
> that can explain a drop in performnace while doing contigous I/O.
> However I didn't expect it to make a difference, or at least not so
> relevant.
> If this doesn't help at all, it might not be an elevator/blkdev thing.
> At least on my machines the contigous I/O still at the same speed.
well, it doesn't help at all. I/O gets more worse with that change. (8mb/s 
less). How can this happen? *wondering*

> You also where the only one reporting a loss of performance with
> elevator-lowlatency, it could be still the same problem that you've
> seen at that time.
The only one? Surely not. Also Con tested your elevator-lowlatency and we both 
saw performance degration :)

> can you try with data=writeback (or ext2) or hdparm -W1 and see if you
> can still see the same delta between the two kernels? (careful with -W1
> as it invalidates journaling)
Yes, I'll do it later this day.

Sorry for my late reply. I've been very busy.

ciao, Marc


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