Faster Booting Via Parallel CPU Bringup Hits A Snag With Older AMD CPUs
Going back to last December when that latest code was posted for supporting parallel CPU bring-up on x86_64, there were reports of problems for some AMD hardware. However, debugging the issue is a challenge with the system getting stuck early on in the boot process with minimal information available and completely crashes/hangs the system.
Finally today is an update on that matter - confirming from additional testing that Zen/Zen+ CPUs appear affected by this issue with parallel CPU bring-up while newer Zen 2 and Zen 3 processors appear to behave fine. Debugging the Zen/Zen+ issues remains a challenge due to failing quickly and not getting any output from the system at boot. Besides Zen/Zen+ being botched with this parallel CPU boot code, previously it was also reported pre-Zen APUs/CPUs having trouble too.
So while this CPU parallel boot support for Intel/AMD x86_64 is promising especially for significant boot time savings with higher core count systems, given the lack of notable progress in recent months it doesn't appear to be much of a priority and also remains complicated by this AMD issue and going through the mailing list there may be some other quirks/issues too. Hopefully they'll be able to sort through these problems otherwise if/when these patches move forward could end up having to blacklist/whitelist CPUs for enjoying this functionality.