Re: [gentoo-user] Performance problem at writing big files and Multitasking

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-----Original Message-----

From: Matthias Bethke <matthias@×××××××.de>



Date: Mon, 26 Feb 2007 17:28:35 

To:gentoo-user@l.g.o

Subject: Re: [gentoo-user] Performance problem at writing big files and Multitasking





Hi Daniel,

on Saturday, 2007-02-10 at 12:49:14, you wrote:

> I will give short overview what i have tried so far.
>
> 1. Trying different I/O Scheduler ( cfq anticipatory and deadline)
> 2. Enabling Low latency kernel and Preemptible kernel
> 3. Setting 1000 HZ for timer frequency
> 4. Tried the new kernel 2.6.19-gentoo-r6 and even the testing version
> 2.6.20-gentoo with core 2 enabled in processor type


Oh, so it is a multicore CPU---sorry if you mentioned it already, I

had deleted the start of the thread already when I read Benno's advice.

In that case, try 100 Hz scheduling period as well. I've had very bad

experiences with I/O and 250 Hz or higher on a dual Xeon. My guess is

that it was a cache effect and therefore shouldn't happen on the

Core2Duo, but it might still be worth a try.



> As i am using Xfce i installed the diskperf-plugin which monitors disk
> I/O. The monitoring is divided in disk-read and disk-write.
> I recognized that every time when reading stops writing starts. So is
> this staggering of writing to disk normal as the programs have to read
> data they want to write to disk? On my previous machine i didn't
> recognize such a behaviour.


So you're reading and writing from/to the same disk? I'd expect that

behavior then, because the I/O scheduler tries to satisfy requests with

as little thrashing as possible. So if there are enough write requests

queued up it may keep the HD busy writing for a while before reading the

next chunk from somewhere else.



cheers!

	Matthias

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