It’s now mid October, there are 0 posts in 2017. Therefore I think it’s time to loosen up posting constraints and try make a bit more casual posts. For a start I will dig up one of the unfinished works. I will start with a quick overview of an old piece of tool (unmaintained) I wrote quite a few years ago. The tool caps the maximum CPU utilisation of a process from userspace without requiring root access. One instance of the process can cap multiple processes individually, in a group or it can also cap an entire process sub-tree. I intended to post about it in great detail, but this time I will keep it brief, and dig deeper in the next opportunity. Let’s get into it.
Motivation (from agony)
A few years ago, I was used to run different CPU intensive experiments on my old laptop, which would sometime run weeks. The CPU temperature used to go up to 95 Deg C. Sometimes it went upto 99 Deg C and then it used to throttle down the cores to get the temperature down. This is definitely not a healthy temperature, therefore I feared of hardware damage. The laptop had a metal case, which became so hot that it left red marks on my thighs. One time an entire chocolate bar melted into a pool of liquid chocolate (someone left it near the exhaust fan). Therefore it was time that I figure something out, such that I can run the experiments, but keep the laptop cool (relatively).
The obvious idea was to cap the CPU usage for the processes. An easy solution is to install a virtual machine and run the code inside the virtual environment. Note that, in my case nice does not work, as it does not help control how much of the CPU a processes utilises when it acquires it. I could have used cgroups, but I didn’t want to (I don’t know why). At that point of time I was feeling the need for Solaris Zones.
Essentially what I wanted is something portable in any *nix system, works completely from userspace and also does not need root privilege. Therefore I made a small tool which does in. It was written in C and POSIX compliant libraries.
Also note that, there is a similiar kind of tool called cpulimit, which I didn’t know existed when I wrote this. This tool works well too.
Given this situation, it was time to write something in-house … drum roll … CPULeash.