PC Processors

[Teadrinker]

Hello

I am a 7900X3D user who uses Linux as OS. This CPU has been very good yet when compared to Windows, it seems its 3d v-cache technology is non-existent on Linux! Is AMD aware? 

I personally have tried disabling CCD1 through BIOS (6 cores without 3d v-cahce) and testing game performances and noticed 0 improvement in all the games that I tried.

Can AMD please support Linux 7900X3D users?

Thank you very much.

Here is some 7900X3D benchmarks (from Phoronix.com):

https://www.phoronix.com/review/ryzen9-7900x3d-gaming/6

As you can see, 7950X3D and 7900X3D have weaker performance than non-3d v-cache CPUs like 7700X for example.

[FunkZ]

The Dual CCD X3D chips have some tweaks that are required to get the best performance. This is due to only one CCD having the extra V-cache. Since the tweaks seem to be Windows-centric, requiring Windows Game Mode and Xbox Game Bar, this optimization may not be available in Linux?

https://community.amd.com/t5/gaming/how-to-set-up-your-system-with-a-new-amd-ryzen-9-7950x3d-or/ba-p...

[tim-rex]

As an indie/aspiring game dev, I really wish AMD provided a path to support optimal usage of the dual CCD layout for gaming (and game development) on Linux platforms

For pure gaming the 7800X3D seems the better option across windows and Linux, but of course I’d like to ensure my code runs optimally on any and all target systems.

For game dev specifically, the 7950X3D probably makes more sense for the additional cores alone (additional overhead of debugging etc) but the picture is unclear where Linux is concerned

[Teadrinker · Accepted solution]

After about 8 months of using 7900X3D on Linux, I've finally learned how to make it's 3D V-Cache cores work on Linux (thanks to CachyOS developer ptr1337 who told me)
You can use Hotplug to disable CCD1 cores (cores without extra cache) using terminal:

echo 0 > /sys/devices/system/cpu/cpu6/online
...
echo 0 > /sys/devices/system/cpu/cpu11/online
echo 0 > /sys/devices/system/cpu/cpu18/online
...
echo 0 > /sys/devices/system/cpu/cpu23/online

When you do this, it is as you have disabled CCD1 using BIOS. You can use this command even in middle of the game! Also you can re-enable all those cores (again, you can alt-tab even in middle of the game) by replacing "0"s with "1" in code above! Hotplug already exists in Linux Kernel code BTW, you don't need to install anything.

You can use "lstopo" command on Linux to find out which cores (and threads) have extra cache. For 7900X3D, it is cores 0 to 5 and threads 12 to 17. Therefore you need to disable all the other cores (6 to 11 and 18 to 23).
This will massively increase CPU gaming performance (depending on the game ofc. For some games you notice no difference and some games for example Starfield HATE extra cache lol) and will truly make use of 3D Cache technology of this CPU under Linux. It turns out this CPU works perfectly on Linux, it was just sad that AMD didn't even bother to make such basic information public for beginner Linux users..