MATLAB Answers


High CPU usage when matlab is idle on Linux

Asked by Livio
on 18 Jul 2012

Hi all, I installed Matlab (R2012a) on a core i5 machine with 4 GiB of RAM. The OS is Ubuntu 11.04 64 bit. Matlab works fine, (apart from some Unix version related issues), but when idle it takes more than 100% CPU. The top command reports:

17162 newcesir 20   0 1137m 382m  70m S  107  4.8   2:35.14 MATLAB
  9 root     20   0     0    0    0 S   21  0.0 898:12.00 ksoftirqd/1
  3 root     20   0     0    0    0 S   19  0.0 923:00.86 ksoftirqd/0
 13 root     20   0     0    0    0 S   10  0.0 779:41.32 ksoftirqd/2
 16 root     20   0     0    0    0 S    0  0.0 640:55.65 ksoftirqd/3

The 4 ksoftirqd processes have something to do with interrupt handling for the 4 processors, and are assciated with the matlab running. The machine is multi user, and having one cpu occupied for every matlab instance started is not good at all. Does anyone know why this is happening? Thank you


on 19 Jul 2012

It happens immediately after starting matlab and doing nothing else. How can this be a normal behaviour? I checked on a collegue's Mac, with a different version of Matlab (Unix matlab, anyway), and the cpu usage on idle was almost 0%

Ken Atwell
on 20 Jul 2012

I am stumped, I would contact support.

Different startup scripts?

Also, I would suggest deleting the MATLAB preferences file and re-creating it.


No products are associated with this question.

1 Answer

Answer by Adam Filion
on 20 Jul 2012
Edited by Adam Filion
on 20 Jul 2012
 Accepted answer

Have you rebooted your Linux machine since July 1? If not then that may be the problem. There was a bug with Linux that caused all kinds of problems with the leap second on July 1:

This bug has caused some strange behavior for various programs, MATLAB included. Rebooting the machine fixes the problem. If that doesn't resolve it then I recommend contacting tech support:

[EDIT fixed links]


on 24 Jul 2013

I am experiencing similar behaviour on my laptop running debian wheezy 64-bit with some unstable packages and R2013a. I reboot it quite often, the CPU usage problem persists:

PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND                                                                                                                                                                        
11485 helmar    20   0 2559m 626m 115m S  51.9 16.1  52:37.03 MATLAB                                                                                                                                                                         
3824 root      20   0  188m  75m  26m S  12.5  1.9  11:36.72 Xorg                                                                                                                                                                           
24046 helmar    20   0  580m  20m  11m S   5.3  0.5   0:02.85 gnome-terminal                                                                                                                                                                 
249 root     -51   0     0    0    0 S   2.3  0.0   0:41.82 irq/21-uhci_hcd 

This however does NOT happen right away after starting Matlab.

Iain W
on 24 Jul 2013

I've just found this thread after experiencing the same issue.

Fresh Ubuntu 13.04 x64 install, fresh R2013a install.

I've just restarted Matlab in an attempt to reproduce the problem, but it hasn't thus far - as above maybe it doesn't do it right away. If I can reliably reproduce I'll post back.

EDIT: Ok, so after reading this comment:

I did some tests. I can confirm that in my case triggering the help (then closing it) causes high idle cpu usage.

To reproduce

1 Start matlab.
2 observe idle cpu usage is low.
3 press F1 to pop up help window, close it.
4 Observe erratic/high CPU usage.

I tried the fix they suggest (changing the help renderer) and that appears to solve the problem for me.

on 2 Aug 2013

Worked for me too!

Discover MakerZone

MATLAB and Simulink resources for Arduino, LEGO, and Raspberry Pi

Learn more

Discover what MATLAB® can do for your career.

Opportunities for recent engineering grads.

Apply Today

MATLAB Academy

New to MATLAB?

Learn MATLAB today!