Detect process eating cpu without: top, htop, ps

cpuprocess

I went thru a problem where I could only guess what process was eating the cpu.

My cpu usage was about 80% for all cores at psensor.

I tried htop, top and ps -A -o pcpu,pid,cmd --sort +pcpu (the last one I even tried with sudo to no avail).
All these shown the culprit pid (that I was aware of) using about 7% only…

When I SIGKILL on that pid, all get back to normal.

To test, I did an infinite loop on terminal while true;do echo -n;done but that I could clearly see at htop; so my guess what was causing trouble was not similar to that…

So I wonder if there are other ways I could have found the culprit without having to guess?

Thinking again, I think I would like to know what calculations psensor and "system load indicator applet" uses that was able to show that value but the others were unable to?

PS.: linking about wait time,
linking about load average

Best Answer

I am not familiar enough with the details to give precise hints but I guess there are two sources of differences between the real caused load and the shown CPU usage:

The process may consist of several threads and top may not sum them up. You can see the number of threads by this:
```
ps -eo pid,nlwp,%cpu,user,args
```
In top you can switch the thread handling with H. The CPU usage of each thread is usually quite low.
The process may cause a lot of I/O. I/O wait time is part of the overall CPU load but may not be part of a process's CPU usage value. So check the wait value in top. It does not tell you which processes cause it to which extent but if the value is low then it cannot explain the effect.

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Debian – How to chase a program who is rising up the laptop’s temperature

I belive atop allows to monitor even short programs. Powertop allows to monitor states of processor. However if the peaks are hardly noticable it is unlikely that it caused this problem.

There are however few possible causes:

Corrected ACPI handling. For some reasons the temperature in ACPI was read incorrectly and the correct temperature was always 15°C highier (or incorrect). Does the computer feels warmer
The newer kernel may have worst temperature management (like lacking p4-clockmod etc.) - it may be bug in kernel.
Previously mentioned dust.

Linux Hardware – Number of Processors in /proc/cpuinfo

The words “CPU”, “processor” and “core” are used in somewhat confusing ways. They refer to the processor architecture. A core is the smallest independent unit that implements a general-purpose processor; a processor is an assemblage of cores (on some ARM systems, a processor is an assemblage of clusters which themselves are assemblages of cores). A chip can contain one or more processors (x86 chips contain a single processor, in this sense of the word processor).

Hyperthreading means that some parts of a core are duplicated. A core with hyperthreading is sometimes presented as an assemblage of two “virtual cores” — meaning not that each core is virtual, but that the plural is virtual because these are not actually separate cores and they will sometimes have to wait while the other core is making use of a shared part.

As far as software is concerned, there is only one concept that's useful almost everywhere: the notion of parallel threads of execution. So in most software manuals, the terms CPU and processor are used to mean any one piece of hardware that executes program code. In hardware terms, this means one core, or one virtual core with hyperthreading.

Thus top shows you 4 CPUs, because you can have 4 threads executing at the same time. /proc/cpuinfo has 4 entries, one for each CPU (in that sense). The processor numbers (which are the number of the cpuNUMBER entries in /sys/devices/system/cpu) correspond to these 4 threads.

/proc/cpuinfo is one of the few places where you get information about what hardware implements these threads of execution:

physical id : 0
siblings    : 4
core id     : 0
cpu cores   : 2

means that cpu0 is one of 4 threads inside physical component (processor) number 0, and that's in core 0 among 2 in this processor.

Best Answer

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Debian – How to chase a program who is rising up the laptop’s temperature

Linux Hardware – Number of Processors in /proc/cpuinfo

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