Parallel CPU Bringup Lands For Linux 6.5 To Shorten Boot/Reboot Time On Large Servers

Written by Michael Larabel in Linux Kernel on 27 June 2023 at 05:43 AM EDT. 3 Comments
The work originating in late 2021 for bringing up secondary CPU cores in parallel at boot-time to help shorten boot/reboot times for large core count servers has finally landed with the in-development Linux 6.5 kernel.

This parallel CPU bring-up is intended to help shave off boot times for large servers, particularly for Kexec reboots commonly used by hyperscalers and other cloud providers to already shorten reboot times in order to bypass the usual and time consuming POST process. Linux already boots quite quickly but this can be all the more important for maximizing the uptime of VMs.

The parallel CPU bring-up code was submitted yesterday via the smp/core pull and has already been accepted into the mainline kernel. It's great to see this work finally land so less of the boot process is locked up in a serialized bring-up.

The code is currently fully-enabled on x86-based platforms. There is the new cpuhp.parallel= kernel parameter if wishing to enable/disable the parallel bring-up. The default handling is set via the CONFIG_HOTPLUG_PARALLEL=
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