Ways to get CPU Utilization on a Linux machine

AnkitAg · 12-12-2015, 01:16 AM

I am running Ubuntu 14.04 on my machine. I need to get the CPU utilization for a process running at a required monitoring interval.

I have tried the following have a few questions about them.
I considered calculating the effective usage between 2 points as follows:

Process run time(P) = utime + stime + cstime + cutime

Total CPU run time(C) = I am getting this value from /proc/stat.

Considering a monitoring interval t, CPU utilization is calculated as

CPU usage = ( P2 - P1 ) / (C2 - C1 ) * 100

Issue:

The value CPU usage read comprises the sum total of all 4 ( on my machine ) cores. But top shows a value divided by 4. I found that there is an Irix mode which if turned on( by default ) gives values multiplied by 4. What I want to know is that which value is correct ? Should I multiply my value by 4 ?.

I want to get the usage at sampling periods of lets say 1ms. But apparently /proc/stat is not updated at the same rate, and nether is top. What is the smallest sampling period that I can go down to with using this method ?
Please let me know. Also if any other sugestions, please let me know. Also can we write a kernel module to do the same at my required sampling rate ? Does any such module exists ?

Thanks
Ankit

Keruskerfuerst · 12-12-2015, 11:32 AM

I think the following:

Processors are numbered as follows:

P1: processor 1
P2: processor 2
P3: processor 3
P4: processor 4
...
PN: processor N

Average:

(P1+P2+P3+P4+...+PN)/N = average of cpu utilization.

I think you can have a look at the source code of "top".