RE: [PATCH RFC 0/3] arm64: Add HOTPLUG_PARALLEL support for secondary CPUs

[Michael Kelley]

From: Jinjie Ruan <ruanjinjie@xxxxxxxxxx> Sent: Thursday, June 11, 2026 6:38 AM
> 
> Support for parallel secondary CPU bringup is already utilized by x86,
> MIPS, and RISC-V. This patch brings this capability to the arm64
> architecture.
> 
> Introduce CONFIG_PARALLEL_SMT_PRIMARY_FIRST to avoid primary SMT threads
> to boot first constraint.
> 
> And Add a 'cpu' parameter to update_cpu_boot_status() to allow updating the
> boot status at a per-CPU granularity during parallel bringup.
> 
> Rework the global `secondary_data` accessed during early boot into
> a per-CPU array. This array maps logical CPU IDs to MPIDR_EL1 values,
> enabling the early boot code in head.S to resolve each secondary CPU's
> logical ID concurrently.

I tested the series on an ARM64 VM running on Hyper-V in the Azure cloud.
Tested with 16 vCPUs in the VM and with 96 vCPUs in the VM. No issues.
I mainly wanted to make sure nothing expected happened with Hyper-V as
the host.

With 96 vCPUs, the secondary CPU startup time drops from ~140 milliseconds
to ~130 milliseconds. That improvement is not as dramatic as you saw on
QEMU, so I presume the difference is due to the hypervisor implementation
of the PSCI calls.

Tested-by: Michael Kelley <mhklinux@xxxxxxxxxxx>

> 
> Jinjie Ruan (3):
>   cpu/hotplug: Introduce CONFIG_PARALLEL_SMT_PRIMARY_FIRST
>   arm64: smp: Pass CPU ID to update_cpu_boot_status()
>   arm64: Add HOTPLUG_PARALLEL support for secondary CPUs
> 
>  arch/Kconfig                   |  4 ++++
>  arch/arm64/Kconfig             |  1 +
>  arch/arm64/include/asm/smp.h   | 14 +++++++++++---
>  arch/arm64/kernel/cpufeature.c |  2 +-
>  arch/arm64/kernel/head.S       | 23 ++++++++++++++++++++++
>  arch/arm64/kernel/smp.c        | 35 ++++++++++++++++++++++++++++++----
>  arch/arm64/mm/context.c        |  2 +-
>  arch/mips/Kconfig              |  1 +
>  arch/riscv/Kconfig             |  1 +
>  arch/x86/Kconfig               |  1 +
>  kernel/cpu.c                   |  6 +++++-
>  11 files changed, 80 insertions(+), 10 deletions(-)
> 
> --
> 2.34.1
>