- 1 How Linux CPU Usage Time and Percentage is calculated
- 2 How can you check the CPU usage on a Windows 98 machine?
- 3 Why does your computer run slow at 2 percent CPU usage?
- 4 When will you have two CPU usage history graphs in task manager?
- 5 When is the CPU Usage History divided into multiple graphs?
- 6 I get a warning on my PC that says my CPU usage is at 80 percent what do i do?
- 7 How do you resolve system idle process high CPU usage?
How Linux CPU Usage Time and Percentage is calculated
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CPU time is allocated in discrete time slices (ticks). For a certain number of time slices, the cpu is busy, other times it is not (which is represented by the idle process). In the picture below the CPU is busy for 6 of the 10 CPU slices. 6/10 = .60 = 60% of busy time (and there would therefore be 40% idle time).
Note: A tick(cycle) is the time it takes to send a single pulse. A pulse consists of a high voltage followed by a low voltage. There can be billions of ticks per second depending on the frequency(GHz) of the CPU clock.
You can get the number of CPU ticks since boot from /proc/stat
- user: normal processes executing in user mode
- nice: niced processes executing in user mode
- system: processes executing in kernel mode
- idle: twiddling thumbs
- iowait: waiting for I/O to complete
- irq: servicing interrupts
- softirq: servicing softirqs
- steal: involuntary wait
- guest: running a normal guest
- guest_nice: running a niced guest
To calculate Linux CPU usage time subtract the idle CPU time from the total CPU time as follows:
Total CPU time since boot = user+nice+system+idle+iowait+irq+softirq+steal
Total CPU Idle time since boot = idle + iowait
Total CPU usage time since boot = Total CPU time since boot - Total CPU Idle time since boot
Total CPU percentage = Total CPU usage time since boot/Total CPU time since boot X 100
If you use the formula on the example data above you should get a Linux CPU usage Percentage of 60%.
Note: Guest and Guest_nice are already accounted in user and nice, hence they are not included in the total calculation
For real time CPU usage, you will need to calculate the time between two intervals.
Below is an example of a Bash Script by Paul Colby that does this