Why % CPU doesn't add up to 100?

Question

Why doesn't the "% CPU" in System Monitor add up to 100? (% CPU is the third column on the following screenshot)

cpu time

Iain Lane · Accepted Answer · 2010-12-05 01:02:40Z

7

Two reasons:

The calculations are per-core. So if you have a dual-core system then the maximum will be 200%.
You will not necessarily see all processes which are using your CPU in System Monitor, so the CPU usage might be below 100% for each processor.

Furthermore it is unusual for 100% of any processor to be in use. See the resources tab for the total in use per processor.

answered Dec 5, 2010 at 1:02

Iain Lane

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1

Ah ok, I'm on a dual core that's why! A bit unintuitive though. Thx.
– Olivier Lalonde
Dec 5, 2010 at 1:22

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Oli · Accepted Answer · 2010-12-05 01:03:18Z

6

Does your do you have more than one CPU core? Or Hyper-Threading (or the AMD equivalent)?

You can see how many CPUs Ubuntu thinks you have by running this:

cat /proc/cpuinfo | grep "^vendor" | wc -l

Ubuntu will count each of these. So if you have 8 CPU's (as I do, quad-core with hyperthreading), you can reach 800% CPU.

answered Dec 5, 2010 at 1:03

Oli♦

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Community · Accepted Answer · 2017-04-13 12:24:34Z

2

There is more information regarding this issue at the askubuntu link below (a question I asked):

CommunityBot

1

answered Dec 5, 2010 at 2:57

Peter.O

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