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Old 10-15-2007, 05:33 AM   #1
Registered: Feb 2004
Distribution: Slackware 12 - dropline Gnome
Posts: 43

Rep: Reputation: 15
Determine cause of high IO Wait on CPU?

Hi all,

I have determined that I have massive IO Waits on my CPU. I'm having trouble figuring out what process is causing it though and what to do about it.

Using iostat I see that the %IOWAIT is really high, sometimes above 80% and for long periods of almost a minute at the time my machine is as good as frozen.

I'm running ubuntu 7.10 beta and I'm kindof suspecting xorg.

So, would anyone be able to help me determine the process that is causing this.

Thanks heaps!

/ dan
Old 10-15-2007, 06:54 AM   #2
Registered: Oct 2003
Location: King George, VA
Distribution: RHEL/CentOS/Scientific/Fedora, LinuxMint
Posts: 370

Rep: Reputation: 44
Is this a multiple disk system?
Server? What server daemons?

I would use ps -auxww and look under the "Start" column to see what actual command has been running the longest.

Get the PID of that command and look for it in /proc

cd /proc/"PID"


watch 'ls -l fd' (Will actually show files being process in realtime)
I like to use watch instead of strace ( My eyes can't keep up with all the fast moving text

Maybe have a seperate xterm pulled up with iostat -d 2 (disk)and iostat -c 2 (cpu)

It will be cat and mouse for awhile but eventually you will find the culprit
Old 10-15-2007, 09:10 AM   #3
Registered: Feb 2004
Distribution: Slackware 12 - dropline Gnome
Posts: 43

Original Poster
Rep: Reputation: 15
Thanks for that, I'm not really sure what to look for through.

The view is just static.

The top file I'm writing to is /dev/null (where I keep all my most important backups )

The system is my good old laptop, core duo 2.16. 2GB ram. 7000rpm 2.5 lappy hdd.

Somehow I don't think ubuntu's kernel is the right choice for me. If I can't figure this out pretty soon I will just compile a vanilla kernel myself.


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