Can a multi-core CPU be run in single-core mode?

[wstrohm]

Is there an accessible command by a user that can cause a multi-core CPU to run on a single core? I'd like to try an experiment. Note that Geekbench 4.2.3 returns both single-core and multi-core test results. How do they do that?

My PPC G5 with dual CPUs can be set to run using only one of the two CPUs, by using a development app from Apple. Is there something that can do the same for an Intel multi-core (i7 8700) CPU?

 

[P1LGRIM]

Is there an accessible command by a user that can cause a multi-core CPU to run on a single core?

cpus=1.

 

[wstrohm]

cpus=1.

Via Terminal? Is that the complete syntax? Thanks!
Oh, and what is the command to return to multi-core operation? cpus=6?

 

[P1LGRIM]

Via Terminal? Is that the complete syntax? Thanks!
Oh, and what is the command to return to multi-core operation? cpus=6?

It is a boot argument you can add it to your config.plist or enter it from the Clover menu.

 

[wstrohm]

Ah, thanks much! (It didn't work using Terminal.)
[Edit: Adding cpus=1 to the Clover menu seems to have worked. At least Geekbench returns no "results" display after running the CPU test... guess it doesn't like failing to see multiple cores on this CPU, so it just puts up its main screen when the test is finished.]

 

[markpotter]

Also - any application that isn't multithreaded is running in single cpu mode.. Thats how geekbench tests it. Most benchmarks have a setting to be run in one thread, as do most of the virtualization packages ... Oracle VirtualBox, Parallels, VMWare etc..

most of these can be forced into single thread mode, so something like
sysbench --cpu-max-prime=XXXXX --threads=1

(homebrew - calculates prime numbers to whatever you put in XXXXX force to 1 thread for single core work.. this syntax is the old setup, and I don't remember how it changed, but, its along these lines.. )