From: Andrew Morton <akpm@osdl.org>
To: age <ahuisman@cistron.nl>
Cc: linux-kernel@vger.kernel.org
Subject: Re: READAHEAD
Date: Thu, 30 Oct 2003 13:44:07 -0800 [thread overview]
Message-ID: <20031030134407.0c97c86e.akpm@osdl.org> (raw)
In-Reply-To: <bnrdqi$uho$1@news.cistron.nl>
age <ahuisman@cistron.nl> wrote:
>
> I have a problem which i don`t understand and i hope that you
> will and can help me. The problem is that i experience strange disk
> read performance. I have to set hdparm -m16 -u1 -c1 -d1 -a4096 /dev/hde
> to get timing buffered disk reads of 56 MB/SEC.
> When i disable readahead i get 17 MB/SEC
> When i enable readahead with -a8 i get 17 MB/SEC
> When i enable readahead with -a16 i get 24,5 MB/SEC
> When i enable readahead with -a32 i get 30,5 MB/SEC
> When i enable readahead with -a64 i get 35 MB/SEC
> When i enable readahead with -a128 i get 39 MB/SEC
> When i enable readahead with -a256 i get 39 MB/SEC
> When i enable readahead with -a512 i get 41 MB/SEC
> When i enable readahead with -a1024 i get 50 MB/SEC
> When i enable readahead with -a2048 i get 50 MB/SEC
> When i enable readahead with -a4096 i get 56 MB/SEC
> With -a8192,-a16384 and -a32768 i get also 56MB/SEC
>
> Before, i never had to set readahead so high
> Please could you tell me, what is going on here ?
Lots of people have been reporting this. It's rather weird.
Is the same effect observable when reading a large file, or is it only
observable via `hdparm -t'?
next prev parent reply other threads:[~2003-10-30 21:42 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-30 19:23 READAHEAD age
2003-10-30 21:44 ` Andrew Morton [this message]
2003-10-31 7:43 ` READAHEAD Nuno Silva
2003-10-31 8:03 ` READAHEAD Andrew Morton
2003-10-31 12:20 ` READAHEAD age
2003-10-31 9:28 ` READAHEAD Andrew Morton
2003-10-31 9:29 ` READAHEAD Andrew Morton
2003-11-01 9:15 ` READAHEAD age
2003-11-03 0:15 ` READAHEAD Derek Foreman
-- strict thread matches above, loose matches on Subject: below --
2005-09-27 2:38 Readahead Alan Stern
2005-09-27 3:06 ` Readahead Randy.Dunlap
2005-09-27 4:24 ` Readahead Andrew Morton
2005-09-28 18:40 ` Readahead Alan Stern
2003-11-01 17:22 READAHEAD Voluspa
2002-04-16 20:21 readahead Andries.Brouwer
2002-04-16 19:10 readahead Andries.Brouwer
2002-04-16 19:23 ` readahead Andrew Morton
2002-04-16 19:33 ` readahead Jens Axboe
2002-04-16 13:54 readahead Andries.Brouwer
2002-04-16 16:08 ` readahead Steven Cole
2002-04-16 18:25 ` readahead Andrew Morton
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