What is the best way to measure "spare" CPU time on a Linux based system

Question

For some of the customers that we develop software for, we are required to "guarantee" a certain amount of spare resources (memory, disk space, CPU). Memory and disk space are simple, but CPU is a bit more difficult.

One technique that we have used is to create a process that consumes a guaranteed amount of CPU time (say 2.5 seconds every 5 seconds). We run this process at highest priority in order to guarantee that it runs and consumes all of its required CPU cycles.

If our normal applications are able to run at an acceptable level of performance and can pass all of their functionality tests while the spare time process is running as well, then we "assume" that we have met our commitment for spare CPU time.

I'm sure that there are other techniques for doing the same thing, and would like to learn about them.

Answer 1

With a multi-core/processor system you could use Affinity to your advantage.

Answer 2

SAR is a standard *nix process that collects information about the operational use of system resources. It also has a command line tool that allows you to create various reports, and it's common for the data to be persisted in a database.

Answer 3

So this may not be exactly the answer you're looking for, but if all you want to do is make sure your application doesn't exceed certain limits on resource consumption and you're running on linux you can customize /etc/security/limits.con (may be different file on your distro of choice) to force the limits on a particular user and only run the process under that user. This is of course assuming that you have that level of control on your client's production environment.

Answer 4

If I understand correctly, your concern is wether the application also runs while a given percentage of the processing power is not available.

The most incontrovertible approach is to use underpowered hardware for your testing. If the processor in your setup allows you to, you can downclock it online. The Linux kernel gives you an easy interface for doing this, see /sys/devices/system/cpu/cpu0/cpufreq/. There is also a bunch of GUI applications for this available.

If your processor isn't capable of changing clock speed online, you can do it the hard way and select a smaller multiplier in your BIOS.

I think you get the idea. If it runs on 1600 Mhz instead of 2400 Mhz, you can guarantee 33% of spare CPU time.