Message-Id: <200401030415.i034FJoc006230@turing-police.cc.vt.edu>
To: Tobias Diedrich <ranma@gmx.at>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Strange IDE performance change in 2.6.1-rc1 (again) 
In-Reply-To: Your message of "Sat, 03 Jan 2004 04:33:28 +0100."
             <20040103033327.GA413@melchior.yamamaya.is-a-geek.org> 
From: Valdis.Kletnieks@vt.edu
References: <200401021658.41384.ornati@lycos.it> <3FF5B3AB.5020309@wmich.edu> <200401022200.22917.ornati@lycos.it>
            <20040103033327.GA413@melchior.yamamaya.is-a-geek.org>
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On Sat, 03 Jan 2004 04:33:28 +0100, Tobias Diedrich <ranma@gmx.at>  said:

> Very interesting tidbit:
> 
> with 2.6.1-rc1 and "dd if=/dev/hda of=/dev/null" I get stable 28 MB/s,
> but with "cat < /dev/hda > /dev/null" I get 48 MB/s according to "vmstat
> 5".

'cat' is probably doing a stat() on stdout and seeing it's connected to /dev/null
and not even bothering to do the write() call.  I've seen similar behavior in other
GNU utilities.  

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