Faster Booting Via Parallel CPU Bringup Hits A Snag With Older AMD CPUs

At the end of last year you may recall the talked about Linux kernel patches for booting systems faster by allowing the parallel bring-up of secondary CPU cores. It's been a while since hearing much about that effort but seems to have hit a snag in that the code is running into problems on early Zen CPUs and older.

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.