Ask HN: How to intentionally throttle CPU on a M1 MacBook?

https://news.ycombinator.com/item?id=33405359

by dsnr • 4 years ago

40 61 4 years ago

news.ycombinator.com

Hi everyone,

I recently had no choice but to upgrade to an M1 Macbook from an Intel-based one. I did not want to upgrade, as I’m working on a software for which performance on mid-range machines is critical, but unfortunately the previous laptop gave up on me. Since M1 macbooks are so much more powerful than previous generations, is there a way to intentionally slow it down to be able to test my program on a slower machine? One way I can think of, is to run the program inside a VM, but that would slow down the development loop.

Thanks for all the suggestions. Now I have the following list of tricks to try (collected from the thread):

- taskpolicy -b -p [pid]

- macOS low power mode (which can even be enabled when plugged in)

- VM with limited CPU and RAM, and shared filesystem with host OS.

- Buy older laptop (not an option at this point, really)

- Stress the machine by compiling the Rust compiler in parallel :)

bombcar4• 4 years ago

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

nordsieck• 4 years ago

I've had quite good luck with CL in the past, and FB Marketplace more recently. I feel much better being able to physically see the device before I pay for it.

That way you can verify that It's been properly reset, and that the description/picture are accurate.

kayodelycaon• 4 years ago

If you don't want to do eBay and you're near a Micro Center, they often have some really old refurbished stuff in stock. Got myself a 2014 Mac mini for $250.

throwanem• 4 years ago

I think it depends on the Micro Center. I've been going to the one in Parkville since it opened, and will keep doing until either it dies or I do. Back in 2015 I got a really nice refurbed 2014 MBP that I still use daily, but a couple years later they dropped a lot of old stock in their Apple section and there's been next to nothing in there ever since - latest models of hardware, a few matching accessories, and that's more or less all there is to it.

I haven't asked about that that I can recall, but my guess is they don't see a lot of margin on that stuff, especially with at least two Apple stores in easy driving distance and most Apple customers tending strongly to favor the latest and greatest. Disappointing, but with the streaming boom then being on the upswing, I really can't blame them for making space to cater to the open-walleted parents of a million infants in Fortnite t-shirts.

Still, if you have a Micro Center nearby and you haven't been, you should go there. It's like what computer stores used to be, back when those still existed.

bluedino2• 4 years ago

I did this once, bought an older MacBook Pro to make sure my app was still 'usable' on an older machine. After about a year the machine didn't get any OS updates, and then a year after that it just died. Wasted my $300.

I have a 2006 Intel MacBook that still works but I've also had 3 year old Macs just quit working.

bombcar4• 4 years ago

In some ways $150/yr to make sure your app was usable may be a worthwhile expenditure.

And if you abuse things like https://github.com/dortania/OpenCore-Legacy-Patcher/releases you can keep running "modern" releases on older hardware.

But it depends on what you're trying to do.

danuker• 4 years ago

Perhaps the devices are worth fixing. I trust Rossmann Repair because of their YouTube videos.

olyjohn• 4 years ago

You bought a used machine, and got 2 years of testing out of it for $300? You got a pretty good deal.

I've also had 3 year old Dells, HPs, Lenovos, ASUS, you name it... all die prematurely. I don't honestly believe that any particular company uses any better quality hardware than another. Not measurably better, at least. You're just gonna win some, and lose some, no matter how much you pay for the hardware. This year's most reliable laptop could have a revision next year that makes it the worst laptop...

With laptops and proprietary desktops especially, it's sometimes worth paying for the extra warranty.

TheRealPomax4• 4 years ago

Sorry, did you say "this computer that only cost me $150 a year but allowed me to test and deploy for its platform on native hardware was a waste of money"? Because it kinda sounds like the completely opposite?

As a counter anecdote, I've done this three times for macs so far, and all of those still work for their intended purpose. The 2011 model even survived overheating due to user error and fried its internal graphics cables but works fine with an external monitor. And sure, they're all stuck on whatever their respective latest operating systems are, but that's fine: they're test/compile machines, not daily drivers. And not all of them: in 2022 the oldest realistic mac target you're looking at is the 2015 macbook pro (i.e. "the good one", that even today's models can still take design lessons from).

And here's the best part: if something in them breaks, replacing the entire machine is only a few hundred bucks. Which you don't have to: you just need to buy a "for parts" with the bits you need still working. Any model that's still being used in the wild still has a decent sized for parts market. You can tell when the world stops using a model when the parts dry up.

dtorres• 4 years ago

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

saagarjha• 4 years ago

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.

nominusllc• 4 years ago

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

switch0072• 4 years ago

I barely notice a performance difference in low power mode.

jurmous2• 4 years ago

There is a significant difference:

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...

unsupp0rted• 4 years ago

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

terhechte• 4 years ago

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.

mzs• 4 years ago

SIGSTOP/SIGCONT in a loop?

yjftsjthsd-h• 4 years ago

Sounds like https://github.com/opsengine/cpulimit

jaimehrubiks• 4 years ago

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

jurmous2• 4 years ago

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...

xenonite2• 4 years ago

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...

dsnr2• 4 years ago

This is some TIL material, and looks like a really viable option.

jonpurdy• 4 years ago

You can also do this with GUI apps like App Tamer※. I use this myself to limit CPU consumption of hidden background apps (but not visible apps in the background), optionally running on the Icestorm cores only as well. Lots of options and ways of being configured.

※ - https://www.stclairsoft.com/AppTamer/index.html

kelsolaar• 4 years ago

Awesome app, thanks for sharing!

gcanyon3• 4 years ago

This makes me want to constrain every web page to the icestorm cores. If a web page wants more than ~5% of a CPU, I want that web page to die.

Actually, now that I think about it, I'm almost tempted to write a script to do just that, and either relegates CPU-hogging processes to the icestorm cpus or just kill -stop <process id> them

juliusgeo3• 4 years ago

I tried to implement what you said on my M1 2020 MBP. Heres's the one liner (albeit using 0% of CPU as the cutoff, and only throttling Safari processes):

  ps axo pid,%cpu,command -r | awk '{ if ($2 >= 0 && $3~/WebContent/ )   { print $1 } }' | xargs -L 1 taskpolicy -b -p

You could set this up to run at whatever interval, and it should work. Using browserbench.org/Speedometer2.0/, before running this one liner I get a score of 274. Afterwards, I get a score of 33.6.

EDIT: Fixed url

dsnr2• 4 years ago

One thing I noticed is that browser tabs each have their own process id. Would applying the policy on the main process affect each child tab process?

AA-BA-94-2A-56• 4 years ago

I had a piece of software that did this, and it turned out the energy-efficient cores are still really fast.

enoch2090• 4 years ago

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.

timwis• 4 years ago

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

timeimp• 4 years ago

Put it in an oven and wait a bit.

0xCAP• 4 years ago

Ever heard of Docker?

booleanbetrayal• 4 years ago

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...

capableweb3• 4 years ago

AFAIK Docker doesn't run natively on macOS so it's running via a VM. And since you're already running it via a VM, might just lose the additional abstraction of Docker and set the limits on the VM directly.

TheRealPomax4• 4 years ago

Why try to mid-optimize though? Even when running with Rosetta, Docker's still faster than an 2015/2016 macbook pro (since we're talking about mid tier machines) so being able to throttle it even further is pretty useful.

usefulcat• 4 years ago

Use a profiler?

bluedino2• 4 years ago

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

marginalia_nu• 4 years ago

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.

bombcar4• 4 years ago

This is 100% true (and different "high performance" machines can operate differently, too).

Some people like to develop on a slower machine (do all their development work on the slow machine) so they catch things, others like to do all the work on the fastest machine they have, and only when nearing completion test things on the slower one. Both have arguments in favor - a decent compromise can be a "build on fast, deploy on slow" where it may be as simple as a shared folder between the two machines with Synergy or even Ventura's built-in equivalent for running the app.

reacharavindh• 4 years ago

This.

Crippling a high Mac is still not going to effectively mimic a low end system. An end user device is a system of queues if you will think like that. The slowest/smallest/busiest link in the system determines the overall experience. Sounds like for your needs, you’re going to need a real low-end system that has real bottlenecks in CPU(speeds, caches, accelerators), mem(capacity and speeds), IO(capacity and speeds).

locutous• 4 years ago

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

gok• 4 years ago

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

xenonite2• 4 years ago

Thank you for your suggestion, but I do not succeed with it.

I fail to take a CPU offline on my M1 mac: "cpuctl: processor_exit(i) failed"

Moreover, I can't discern the core type from the cpuctl list since all cpus are of the same "type".

I assume it is easier to activate the "power safe mode" then. Of course, the disadvantage of these approaches is that the whole system gets slower.

zffr• 4 years ago

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.

londons_explore• 4 years ago

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.

jspash• 4 years ago

something something Electron.

TheRealPomax4• 4 years ago

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

mrlonglong• 4 years ago

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

Tagbert• 4 years ago

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.

factorialboy• 4 years ago

I use Zoom. CPU and battery drain.

Ask HN: How to intentionally throttle CPU on a M1 MacBook?

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