From: Andrew Morton <akpm@osdl.org>
To: "John Chatelle" <johnch@medent.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: High read Latency test (Anticipatory I/O scheduler)
Date: Fri, 20 Feb 2004 17:22:29 -0800 [thread overview]
Message-ID: <20040220172229.736cb249.akpm@osdl.org> (raw)
In-Reply-To: <20040220202023.M9162@medent.com>
"John Chatelle" <johnch@medent.com> wrote:
>
> #StreamingRead.sh --simple 4 line shell script:
> while true
> do
> cat ../data/oneGBfile >/dev/null
> done
>
> #WHR.sh -- simple 2 (or 3) line shell script.
> StreamingRead.sh &
> time find /usr/src/linux-2.4.20-18.7 -type f -exec cat \
> '{}' ';' > /dev/null
Note that the latter test runs `cat' once per file: over ten thousand
times. You should also test:
time (find /usr/src/linux-2.4.20-18.7 -type f | xargs cat > /dev/null )
which will run `cat' only some tens of times.
For the anticipatory scheduler, this makes a significant difference - the
run-cat-once-per-file problem has specific fixes and perhaps they're not
working right at present.
And yes, please describe your disk system, tell us the tag depth (if it is
scsi) and try Nick's patch, thanks.
prev parent reply other threads:[~2004-02-21 1:20 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-02-20 20:20 High read Latency test (Anticipatory I/O scheduler) John Chatelle
2004-02-20 21:29 ` Dave Olien
2004-02-20 22:40 ` Nick Piggin
2004-02-21 1:22 ` Andrew Morton [this message]
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