I'm using Ubuntu and every couple minutes it goes unresponsive for a half second to a full second, which isn't normally a problem but makes trying to code extremely frustrating when your trying to hit backspace or navigate the code and nothing is happening. The problem is, the freezes are so brief that top doesn't have time to show me what is spiking the CPU (assuming something is, but I don't know what else could cause this).

Does anyone know how to troubleshoot this performance issue?

Edit: I've tried login in with Gnome Classic (No Effects) instead of Unity but it still freezes up every once in awhile.

Edit: The CPU graph doesn't seem to be showing any actual spikes so it seems you were right and my original diagnosis of CPU spikes being the problem was incorrect, I now suspect IO wait. I don't recall this happening for the brief few weeks I had Windows 7 Starter running on it though, which leads me to believe it isn't (just?) the hardware.. is there anything I can tweak to improve this? I'm using an Acer Aspire One D257, with Ubuntu 11.10.

Edit: Output of dmesg is at http://paste.ubuntu.com/1060054/ and kern.log is at http://paste.ubuntu.com/1060055/

  • This question is interesting both in general case, and your particular one. Mar 28, 2012 at 20:24
  • 1
    By turning on a CPU graph, you can know for sure if it is a CPU spike that's causing the slow down. I/O might be another culprit, or network lag in some cases. Does it happen no matter what program you are actively using at the time? Mar 28, 2012 at 21:07
  • Excellent point David, I'll do that. I only ever use Vim and Firefox on this machine, they're always open and it happens no matter which is in the foreground. At first I thought it was automatic ctag generation from Vim, but after commenting out that section, and wiping out my entire vimrc file, the issue still occurs. I'll try the graph to see if it is indeed a CPU spike or IO wait. Mar 29, 2012 at 0:59
  • How unresponsive does it get? Does your mouse pointer stop updating?
    – AdamKG
    Mar 29, 2012 at 17:25
  • Sorry for the delayed response, I think it freezes the pointer as well, but it's stopped happening or I haven't been noticing it as much lately. Interestingly, I've also had my encrypted USB backup drive plugged in and mounted much of the time lately as well which has me wondering if that could be related. I'm trying to do some more testing with and without the drive plugged in to determine if A) it's related and B) the pointer stops responding during these freezes. Mar 30, 2012 at 4:12

4 Answers 4


There are two additional tools that you may want to check out:

If you don't get what you want from those two tools, then you may need to use developer-tools like OProfile or Sysprof.

All the tools listed are available from ubuntu repositories

Regarding your observation with usb, from what I've heard, some usb-controllers behave a bit flaky with certain hardware which can cause Interrupt-storms, this could cause what you are describing. Try searching for usb interrupt storm and you will get quite a few hits.

  • Hm, I certainly will look into interrupt storms, but the problem has continued to occur even after I've stopped using usb devices on this system so regularly. Much of the time I'll be programming on the way to work (transit) and that's when I'll notice it. Jun 27, 2012 at 11:39

I used htop for years and I finally found how to get Cpu Utilization by numbers and percentages, I am surprised I have missed this.

htop iowait image

Press F2

Arrow to "Available meters"

Highlight CPU average

F5 or F6 to add to column

Arrow to the item "CPU [Bar]"

Press F4 till you get "CPU [Text]"

You can also get IORates




The best way to see this is to use a command-line application like top or htop Install htop.



You would need to be watching it for a while though until you see what causes the spike (if it is indeed a spike in CPU usage and not in i/o wait, which may not be caught in all cases).

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    I'm familiar with top but not htop, does htop indicate IO wait / how do I interpret that part of it's output? I checked the FAQ on the htop website but it didn't mention IO wait. Mar 30, 2012 at 4:08
  • @JefWelling: it does not afaik. Both will show it as CPU usage however.
    – RolandiXor
    Mar 30, 2012 at 4:53
  • There's an additional monitor for I/O activities. It's called iotop (see danjo133s answer).
    – FuzzyQ
    Jul 2, 2012 at 11:14

A new and very helpful tool is cpustat It has a graphical interface that allows you to monitor multiple pids over time.

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