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FIRESTARTER
FIRESTARTER: A Processor Stress Test Utility. This repository contains the source code generator. Our releases (including the generated source code and precompiled binaries) are available at https://tu-dresden.de/zih/firestarter/.
Firefox probably have used more CPU time while I was composing this comment - thanks to JS (in other tabs, HN is a rare example of a site which doesn't abuse my CPU). FF is almost always on the 1st line in top.
If you'll check top/powertop and a typical desktop or a server you'll likely find better targets than 'yes' to reduce energy use.
[1] https://github.com/freebsd/freebsd-src/blob/main/usr.bin/yes...
Convenient for low level testing, but if you want maximum thermal generation there is no substitute for FIRESTARTER:
https://github.com/tud-zih-energy/FIRESTARTER
With my system hooked up to a watts up (but including the monitor and a couple of other things) yes > /dev/null on each core gets a bit above 42w, openssl speed on each core occasionally gets above 45w and running FIRESTARTER for a bit gets above 57w (on an i5-6260U (NUC) with hyperthreading disabled, 15W TDP with some attempted power restraint in the BIOS, firefox on decent websites like HN tent to use about 31w and I think that is something like 10-15w measuring the computer only).
FIRESTARTER has some evolutionary algorithms as well, but at least on my CPU after hours they were still doing much worse than the default. I was wondering why there wasn't much discussion of BIOS power settings that I could find and after some testing found out that they are not effective at restraining max power use (I forget if they had any effect on typical power use either but I don't think it was much if they did). Also, the integrated GPU can use more power than the CPU and can't be limited. For that GpuTest is handy (but not open source):
https://www.geeks3d.com/gputest/
For me on the internal GPU, Pixmark Piano and Furmark use the most power, either can get 60-61w and adding FIRESTARTER in the background only adds another w or two.
Similarly, checking temps with turbostat (PkgTmp), 2x yes seems to max out about 70, testing one of the higher power openssl tests on each core reaches 75, FIRESTARTER alone quickly reaches 80 and slowly ramps up to 90, and adding gputest got up to 96. Interstingly, the max temperature is reached when the CPU dethrottles too quickly after the gputest is done. It takes a few gputests alone in a row to get into the 80s (I got bored after 2x each alternating Furmark and Piano that hit 83). Similarly, looking at power useage with turbostat the max PkgWatt with yes is 8.26, with openssl speed ecdsa 9.88, with FIRSTARTER alone 17.62, + gputest 19.97 (or gputest alone, seems unreliable).
Anyway, this is a long diversion to say that even fancy yes or openssl speed tests are not that great as CPU stress tests :).