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I have a RHEL box that I need to put under a moderate and variable amount of CPU load (50%-75%).

What is the best way to go about this? Is there a program that can do this that I am not aware of? I am happy to write some C code to make this happen, I just don't know what system calls will help.

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10 Answers 10

up vote 14 down vote accepted

This is exactly what you need: http://weather.ou.edu/~apw/projects/stress/

From the homepage: "stress is a simple workload generator for POSIX systems. It imposes a configurable amount of CPU, memory, I/O, and disk stress on the system. It is written in C, and is free software licensed under the GPL."

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This worked perfectly for me in a virtual environment. –  Tim Jun 26 '12 at 20:33

Find a simple prime number search program that has source code. Modify the source code to add a nanosleep call to the main loop with whichever delay gives you the desired CPU load.

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One common way to get some load on a system is to compile a large software package over and over again. Something like the Linux kernel.

Get a copy of the source code, extract the tar.bz2, go into the top level source directory, copy your kernel config from /boot to .config or zcat /proc/config.gz > .config, the do make oldconfig, then while true; do make clean && make bzImage; done

If you have an SMP system, then make -j bzImage is fun, it will spawn make tasks in parallel.

One problem with this is adjusting the CPU load. It will be a maximum CPU load except for when waiting on disk I/O.

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You could possibly do this using a Bash script. Use " ps -o pcpu | grep -v CPU" to get the CPU Usage of all the processes. Add all those values together to get the current usage. Then have a busy while loop that basically keeps on checking those values, figuring out the current CPU usage, and waiting a calculated amount of time to keep the processor at a certain threshhold. More detail is need, but hopefully this will give you a good starting point.

Take a look at this CPU Monitor script I found and try to get some other ideas on how you can accomplish this.

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It really depends what you're trying to test. If you're just testing CPU load, simple scripts to eat empty CPU cycles will work fine. I personally had to test the performance of a RAID array recently and I relied on Bonnie++ and IOZone. IOZone will put a decent load on the box, particularly if you set the file size higher than the RAM.

You may also be interested in this Article.

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A Simple script to load & hammer the CPU using awk. The script does mathematical calculations and thus CPU load peaks up on higher values passwd to loadserver.sh .

checkout the script @ http://unixfoo.blogspot.com/2008/11/linux-cpu-hammer-script.html

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You can probably use some load-generating tool to accomplish this, or run a script to take all the CPU cycles and then use nice and renice on the process to vary the percentage of cycles that the process gets.

Here is a sample bash script that will occupy all the free CPU cycles:

while true ; do
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Or straight from a terminal you could type: while true; do true; done –  Jesse Jun 14 '10 at 23:51
This will load a CPU to 100% CPU but nice and renice won't allow to tune this load, only to weight it with competing processes, if any. –  jlliagre Jun 28 '12 at 6:13

Lookbusy enables set value of CPU load. Project site

lookbusy -c util[-high_util], --cpu-util util[-high_util]

i.e. 60% load
lookbusy -c 60
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Not sure what your goal is here. I believe glxgears will use 100% CPU.

So find any process that you know will max out the CPU to 100%.

If you have four CPU cores(0 1 2 3), you could use "taskset" to bind this process to say CPUs 0 and 1. That should load your box 50%. To load it 75% bind the process to 0 1 2 CPUs.

Disclaimer: Haven't tested this. Please let us know your results. Even if this works, I'm not sure what you will achieve out of this?

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Use the "nice" command.

a) Highest priority: $ nice -n -20 my_command


b) Lowest priority: $ nice -n 20 my_command

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