Re: [2.6] system is very slow during disk access

Michael Buesch
2003-08-07T09:53:54Z

On Thursday 07 August 2003 06:13, Nuno Silva wrote:
> Hi!

Hi,

> There are some references to: hdparm -a 512 /dev/hda.
> For some folks this improves fs performance.
>
> Does it work for you?

Changing read-ahead doesn't work. Neither to 8 nor to 512.
I think it doesn't have something to do with read-ahead,
because the system-performance-drop occurs while
writing to the disk.
My dd-example wrote to disk:

dd if=/dev/zero of=./t.test

I just ran a few other tests:

dd if=/dev/hda of=/dev/null
doesn't drop system performance and the system is very usable
while dd is running.
So reading from a plain partition is OK.

dd if=/dev/zero of=/dev/hdc7
This slows down the system _very_ much, but it's still usable.
The mouse curser doesn't jump randomly over the screen, like it
did while
dd if=/dev/zero of=./t.test

So my guess, it may have something to do with reiserFS.
So I ran another test:

I did
mke2fs /dev/hdc7
mount /dev/hdc7 /mnt/data_1
cd /mnt/data_1
dd if=/dev/zero of=./t.test

And now the surprise. :)
Here the system-behaviour is exactly the same, as while
writing to the plain partition.
The cursor is not smooth, but it's usable and it doesn't
jump ramdonly over the screen.

So I think it has something to do with reiserFS.
Where can I start to track it down, why reiserFS
is doing this?
Hmm, I'll try to enable
CONFIG_REISERFS_CHECK
and
CONFIG_REISERFS_PROC_INFO

Can somebody tell me how to debug reiserFS with these
options enabled?

> Regards,
> Nuno Silva

Short note: hda and hdc are both exactly the same devices.

- --
Regards Michael Buesch [ http://www.8ung.at/tuxsoft ]
Penguin on this machine: Linux 2.6.0-test2 - i386

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