I have a new laptop Lenovo ThinkPad L520 (7859-5BG) Core i5-2520M(2.5GHz) with 4GB RAM.

Having installed Ubuntu 11.10 32-bit, while browsing with Chrome on GNOME classic (no effects), I noticed 173% CPU usage by chrome browser process, and the system slowly got very very slow,

Now, at this stage as I removed the power adapter, the system suddenly got faster (and stopped the lagging behavior) and CPU usage drops down to 48% !!

Observation 1:

I was browsing through chrome when my system seemed to be seriously lagging, so I killed chrome to see if it gets any faster. But there remained no difference. Notice that CPU usage was a bit strange here. It showed no high activity, but as soon as I would click on applications in gnome panel, it would shoot CPU usage to 70, or 80 or 90 or 143% etc. depending on how quickly i clicked back and forth. At this instance I removed by AC adapter of my laptop, and suddenly system got fine. So i again clicked on gnome panel, and noticed that it now took only 7% or 12% or 13% at max, with same kind of clicks in application menu.

Observation 2: At the other times, with AC adapter plugged in, top indicates four instances of chromium taking 90%, 60%, 47% and 2% (for example), and then once I take out the AC adapter same processes take lesser CPU all of a sudden

Intermediate conclusions: What does this indicate ? I cannot figure out any "other" process in "top" that is suddenly being triggered, its the same process that hogs up my CPU once AC power is plugged in !

NOTE: the problem is now CONFIRMED, as i can repeat that when I have power adapter plugged in !

Can anyone tell me what exactly does this indicate ? What is wrong, is it some bug with power management or what ?

  • Are you sure it's 173%? – Artem Koshelev Feb 21 '12 at 13:46
  • Well it shot to this high from 90-95% initially, and the system started lagging when eventually i could either plug adapter out or restart ! – Aamir Feb 21 '12 at 14:17
  • Actually I am struggling to sort out why my system starts lagging severely (dead slow) if i play just one online video and the above observation is a result of some debugging. – Aamir Feb 21 '12 at 14:36
  • @ArtemKoshelev: assuming you're referring to the fact that the CPU usage is over 100%: that's because he has multiple CPUs (according to the operating system). A 2-CPU system can go to 200%, and 4-CPU system to 400%, etc. – Mei Feb 21 '12 at 16:07
  • There's a bug report here, please take a few seconds to sign it if you are having this problem too, then it will get fixed faster! bugs.launchpad.net/ubuntu/+source/linux/+bug/887793 – user78047 Jul 19 '12 at 16:50

Most likely there is some program that runs when AC is plugged in which is taking too much CPU.

The best way to determine the cause is to use the terminal and one of the tools top, atop, or htop. If you understand processes, then what these tools show you will probably make sense; even so, these tools will show you the most CPU-intensive processes at the top when you run them with no switches or options.

If you are new to the command-line, here is a description of what to do:

  • Run the terminal application.
  • When you get a display, run the following command string: sudo top (or sudo atop or sudo htop)
  • Look at the list of processes and see what the top ones are.

The top processes will be taking all of the CPU when your problem arises.

  • Thanks David, I tried "top" etc. for process monitoring but could not get something substantial. Could not repeat the high CPU usage, which usually remains around 50% when a video is being watched in chrome. Is this chrome-browsers usage normal for you all too when you watch an online video ? – Aamir Feb 23 '12 at 1:27
  • As soon as, i plug in adapter slowly the same processes (e.g. chrome, acroread etc. that i usually use a lot) start increasing the cpu usage. So a normal chrome process with 10% cpu usage slowly touches 90% or so. And then everything is choked, until i remove the ac adapter. As soon as I remove it everything gets fine and CPU usage drops back to 9% - 12% from chrome (for example). Pleeease help me ! – Aamir Mar 14 '12 at 22:13
  • Very strange indeed. I would crack out the high-tech hacker chops... if you're up to it, run script then strace some-suspect-program and see what happens when you plug in. When done with strace, use ^C to exit and then the exit command to stop the script command - script will save the output to a file for you. – Mei Mar 15 '12 at 0:23
  • Thanks for your input. The problem is there is no specific process you can look at! Just about any process can go that high, even nautilus can consume upto 70% with just a bit of rash mouse movement, when such a lag occurs (due to the plugged in adapter). Again, notice that its slowly starts lagging, not just immediately upon adapter plugin. But lagging stops just immediately upon removal. Since strace has so much of material, how can one debug it there ? – Aamir Mar 15 '12 at 21:38
  • Look at it the other way around: this means you can use strace on just about anything. I'd also fire up terminal sessions with top, vmstat, and iostat if you are comfortable with these tools: when things start happening, see what the terminal is saying. If you really have to go hardcore to solve this, there is always systemtap (to see what the kernel is doing). This problem you're having really is odd. – Mei Mar 16 '12 at 17:14

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