I've seen the CPU usage go over 100%. How is this possible? Is it because I have four CPU cores, so 100% isn't really the max?
Also, when a program does this, what else can I do in top besides using the
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From the top man-page
k: %CPU -- CPU usage The task's share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time. In a true SMP environment, if 'Irix mode' is Off, top will operate in number of CPUs. You toggle 'Irix/Solaris' modes with the 'I' interactive com- mand.
So, yes, top shows CPU percentage PER core, but you can toggle this behaviour be pressing 'I'.
Yes, if a process in top goes over 100% or top shows >1.0 in load, this means that more than one core is occupied, or the system is oversubscribed. Oversubscription means that there is more work to be put onto the core than is phsyically manageble.
top you can also sort the view by different parameters (like used memory). If you want to look what you can sort by, refer to the help or man page for
You can also see all kind of information about the processes themselves, like Virtual or resident memory used by the process and if it's sleeping or currently running, as well as cpu time used.
The load average in the top, if needed, can also be viewed by the
If hyper threading is enabled, the CPU usage shown in
top is the usage per CPU, not core. For example, on a server with 24 cores and 2 threads per core (total of 48 CPUs), the usage could go up to 4800. Running
lscpu -p provide a decent print of the cores and CPUs:
$ lscpu -p # The following is the parsable format, which can be fed to other # programs. Each different item in every column has an unique ID # starting from zero. # CPU,Core,Socket,Node,,L1d,L1i,L2,L3 0,0,0,0,,0,0,0,0 1,1,0,0,,1,1,1,0 ... ... ... 46,22,1,1,,22,22,22,1 47,23,1,1,,23,23,23,1
I did the following steps to verify the above answer:
$ while true; do x="reee";x="asdasd";z="asdasdasd;"; done
topand verified bash is using around 100% cpu:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 14791 hpaknia 20 0 129156 5188 1856 R 99.7 0.0 28:08.54 bash
1to see the per CPU usage. Only CPU thread 3 out of 48 CPUs is using 100% CPU:
%Cpu3 :100.0 us, 0.0 sy, 0.0 ni, 0.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
In my case each core has 2 CPU threads. If
top percentage showed the per core usage, the value must have been 50% but it's not. Because
top shows per CPU thread usage.