Score:4

I changed cpus from a 3900X to a 3950X but now Ubuntu will only use the original 24 cores. Cores 24-31 are permanently offline after each reboot

ca flag

I changed cpus from a 3900X to a 3950X but now Ubuntu will only use the original 24 cores. Cores 24-31 are permanently offline after each reboot.

I have tried multiple times to change the online file from 0 to 1 for cores 24-31. I edit the file as root and save it.

I have echoed 1 to each cpu file. Same difference.

Lscpu then shows all the 32 cores available.

But after a reboot those online file have reverted to 0. What is changing those files back after I change them to 1?

I don't want to have to edit those files after each reboot. I want them permanently enabled.

So what can I do? Or what mechanism is changing the files automatically so I can stop that?

Nmath avatar
ng flag
Boot into a live session from installation media to see if the problem still exists. If all cores are utilized in the live session, you should reinstall the OS. This is best practice anyway: your OS was installed on different hardware.
Keith avatar
ca flag
I will try that. Strange. . I have swapped cpus many times before. Even between vendors from Intel to AMD on the same software installation and never had one issue where Linux didn't just pick right off from where I left it before the upgrade. This is the first time it has not detected the change in cpu and made adjustments on its own automatically during the first reboot after the change.
Keith avatar
ca flag
Booted a Ubuntu 20.04.1 LTS installation media image and lscpu reports all 32 cores there and available. So will have to reinstall the OS. Downloading 20.04.2 LTS now. Wish there was an easier fix.
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