Solved How to make sure that Core Boost is enabled on AMD EPYC?

[wichtounet]

Hi,

I am currently experimenting with an AMD EPYC 7302 on a two-sockets system with FreeBSD 12.1.

l need to check if Core Performance Boost is working on this system.
I checked the frequency levels that are available:

dev.cpu.0.freq_levels: 3000/3300 2400/2400 1500/1350
dev.cpu.0.freq: 3000

I was actually expecting to see a 3001 indicating the Core Boost but maybe my expectations are incorrect.

So, how to make sure that Core Performance Boost is enabled and active on FreeBSD 12.1?

Thanks

Baptiste

 

[Mjölnir]

sysrc economy_cx_lowest=Cmax
sysrc performance_cx_lowest=Cmax
sysctl hw.acpi.cpu.cx_lowest to see your current setting (mine is C8 on an Intel machine).
grep -i cx /etc/sysctl.conf /boot/loader.conf just to make shure these are not set there.
The frequency boost is done via CX CPU state transitions. C1, C2 & C3 are power saving modes, higher values are for the frequency boost. So you need to make shure the power saving modes do no harm. On decent modern systems, this should be ok. https://duckduckgo.com/?q=CPU+state

 

[wichtounet]

Thanks for your answer mjollnir !

This is very helpful! In the meantime, I have found another solution that is to use performance counters and only one CPU-application and I could see that frequency rise to the correct Core Boost Frequency!

 

[Eric A. Borisch]

Thanks for your answer mjollnir !

This is very helpful! In the meantime, I have found another solution that is to use performance counters and only one CPU-application and I could see that frequency rise to the correct Core Boost Frequency!

Did you need to do anything to enable it, or is the core boost self-managed by the CPU?

 

[wichtounet]

Did you need to do anything to enable it, or is the core boost self-managed by the CPU?

In my case, it was already enabled by the CPU. But I could disable it in the BIOS. So, it could be disabled by default on some computers.

 

[Eric A. Borisch]

I finally ran some compiled tests to determine that, and I could see that boost was working. If I lowered the base rate (dev.cpu.0.freq) it tracked correctly, but I had to patch the kernel to be able to raise the rate back up without a reboot.