Experimental Patches Allow Much Faster AArch64 & RISC-V Kexec Kernel Reboots

Written by Michael Larabel in Linux Kernel on 22 August 2022 at 04:57 AM EDT. 1 Comment
For those making use of Kexec reboots for booting to a new kernel without fully bringing down the system to reduce the server downtime from POST'ing and other hardware initialization tasks, Kexec reboots may soon be much faster on 64-bit Arm and RISC-V systems.

Currently carrying out a Kexec reboot on RISC-V and 64-bit Arm can be rather slow for high core count systems since the code path taken on those architectures ends up tearing down the CPUs serially.

Patches sent out today clean-up the code taken on those architectures for bringing CPU cores down and allow for parallelism. With these patches and an 80-core Arm server, a Kexec reboot can go from taking around 15 seconds to now just around one second.

Ampere Altra Max and other high core count 64-bit ARM and RISC-V systems could soon enjoy faster Kexec reboots. On a 80-core system it can mean the difference of 15 seconds vs. 1 second.

The patches working on this greater parallelism for Kexec reboots on 64-bitArm and RISC-V is currently under a "request for comments" flag on the kernel mailing list. Other CPU architectures like x86_64 and POWER already take a different route during Kexec reboots that aren't currently bottlenecked by the serialized shutdown of the CPU cores. With a bit of luck, these 10 patches to speed-up Kexec reboots could soon be mainlined.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter, LinkedIn, or contacted via MichaelLarabel.com.

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