From: "Martin A. Fink" <fink@mpe.mpg.de>
Organization: MPE
To: linux-kernel@vger.kernel.org
Subject: SATA Performance with Intel ICH6
Date: Fri, 24 Nov 2006 14:07:01 +0100
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Dear all,

I found out, that writing to a SATA harddisk costs around 20% of the
computers cpu time. I write blocks of 1MB size to a file. Write performance
is around 51MB/s what I think is really good. My computer has an Intel ICH6
chipset and a 3.2GHz Pentium 4 processor.
If I understand the design of this chipset correctly, then I would have
expected, that the CPU needs to do only few work, instead I found out, that
writing to disk seems to be really hard work for the CPU.

Can I do anything to optimize writing from memory to disk?

My final aim is to get around 140MB/s of data from 3 different Gigabit
Ethernet cards and store it on 3 harddisk drives that perform 50MB/s.
>From the SATA bus side there should be no problem. Each of the 4 SATAs on
this ICH6 chipset are capable of 150MB/s.

So what makes my CPU that slow? Is it a hardware problem or a problem of
SATA driver of my operating system?

time dd if=/dev/zero of=test.zero bs=1M count=1000
results in

real 0m52.561s
user 0m0.003s
sys  0m7.407s

and strace dd... gives among other information
6.84s 1004calls syscall: write

So I spend 45s of 52s within the kernel. Why so long?


By the way: I'm working with SuSE Linux 9.2 on a Dell Desktop PC, 1GB RAM

Thank you for answers,

Martin
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