How to intentionally throttle CPU on a M1 MacBook?

The M1 chips have two types of cores: high-performance "Firestorm" cores and energy-efficient "Icestorm" cores, which are much slower.

It is indeed possible to constrain a process to the Icestorm cores using taskpolicy:

> taskpolicy -b -p 567

where 567 needs to be replaced by the process id.

Reference: https://eclecticlight.co/2022/10/20/making-the-most-of-apple...

I understand it's not what you want to hear, but I think the only viable option is to test on real low powered hardware.

A throttled high-end machine will not behave like a low-end machine. Sure, they'll superficially both be slow, but not slow in the same way. There are differences in IOPS, cache sizes, and so forth you simply can't escape from.

Especially in low-end laptops, you may also have uneven performance from thermal throttling.

If anyone needs to do this with an Intel-based MacBook Air 2020 model, the answer is much simpler: join a Google Meet call.

Docker Compose allows for resource limits which can be useful for testing harnesses. I know this works locally for v3.9:

  version: '3.9'
  services:
    some-container:
      deploy:
         resources:
           limits:
             cpus: '0.5'
             memory: 1.5G
           reservations:
             cpus: '0.5'
             memory: 1.5G

Reference: https://docs.docker.com/compose/compose-file/deploy/#resourc...

Honestly just buy an older laptop on eBay. Depending on how slow you want, they’re very cheap.

There are many ways to stress the machine or deprioritize your program so that it behaves worse. That said, actually getting performance that is in-line with what your users on old machines would see is generally not easy to achieve. What are you working on? Perhaps there might be something that can be done specifically for your workload.

M1 has a low power mode in the battery section which limits CPU performance.

Geekbench scores with normal and low power mode

- Single core Normal/low power - 1749/1053

- Multi core - 7739/4491

https://www.reddit.com/r/MacOS/comments/qj13bv/m1_macbook_ai...

taskpolicy seems to be the tool https://keith.github.io/xcode-man-pages/taskpolicy.8.html

`sudo /usr/bin/cpuctl` can turn off cores, so for example you can turn off the performance cores.

Depending on what your program is, you might be able to just do some testing on a users machine.

I sometimes use a remote desktop tool (eg. teamviewer) to troubleshoot my software running on a users machine (with the user on the phone normally).

It's usually the quickest way to understand what issue a user is having, and the user walks away thinking they're getting great customer service.

It could be a good way to get a rough feeling for which areas of your software perform well/badly on a low end machine. One benefit is you get to experience it the way a user does - so the interactions with a 7 year old copy of norton antivirus, one of 13 programs running at once with 1GB of RAM, the fact the user has an always-on-top program that is blocking some of the UI but they don't know how to move it, etc.

Why a VM would slow down the loop? You can have shared directories and you can communicate between the two

VM is still an option, many VMs today allow easy file exchange between the host and the VM, with proper configuration you can still code and compile in your original workflow, and test in the VM.

Was just buying an old mac from ebay not an option? Tons available still, I've bought several for that purpose over the years.

If you run something very performance hungry at the same time, the M1 will slow down considerably. Two things that constantly maxes out my M1 is either compiling the whole Rust compiler / toolchain (which is like 30min of heavy load) or rendering something complex in blender (with the Cycles renderer) which easily taxes the M1 for hours.

I know that you don’t want to spend money on a test machine but you might want to check on used laptops through eBay or Craigslist or Offerup. Or someone here might have an older laptop sitting around.

Does your program require macOS? If not, maybe you could run the program on a low-end machine from AWS/GCP. With terraform its pretty easy to create/destroy a VM on demand for testing.

something something Electron.

That's easy, just use your bare hands to throttle that thing. Whether you succeed or not, depends on your strength.

What about running a Virtual Machine and not giving it much ram and CPU to work with?

Do any of the Mac Mini hosting providers offer hourly/daily rental?

You can force processes to the e-cores. That should be plenty slow :P

Use a profiler?

I use Zoom. CPU and battery drain.

SIGSTOP/SIGCONT in a loop?

There is a low power mode you can turn on in battery settings.

Ever heard of Docker?

Put it in an oven and wait a bit.