Linux Parallel CPU Start-Up Restored For AMD CPUs To Yield Faster Boot Times

Written by Michael Larabel in AMD on 8 February 2023 at 07:30 AM EST. 5 Comments
The very promising work around parallel CPU bring-up to speed-up Linux kernel boot times with today's high core count servers and HEDT systems has been revised once more. Notable with the v7 patches is re-enabling support for this time-savings boot feature for AMD processors.

This work to bring-up secondary CPU cores in parallel than sequentially as currently done by the Linux kernel has shown to provide significant time savings for initial boot times on x86_64 systems and servers.

The AMD support though for this boot-time savings was disabled over hitting issues with some older AMD platforms. Fortunately, that appears to be all addressed with the updated patches and AMD CPUs are no longer black-listed from this feature. With the v7 patches, the parallel start-up of secondary CPUs is only disabled though if AMD SEV-ES is activated or other certain conditions around X2APIC.

AMD EPYC processors

Usama Arif of Bytedance sent out the v7 patches on Tuesday with the work that was started by Amazon's David Woodhouse and Intel/Linutronix's Thomas Gleixner. Aside from working out the AMD support, the v7 patches also have other minor changes.

The v7 patches are still tested to yield around an 85% improvement in boot speed when testing with 128 CPU cores split across two NUMA nodes. Now with AMD support restored, it will be fun to see the start-up improvements when dealing with EPYC 9004 "Genoa" that have up to 96 physical cores per socket or Begamo coming with 128 cores per socket.
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