CONFIG_RISCV_BOOT_SPINWAIT: Spinwait booting method

General informations

The Linux kernel configuration item CONFIG_RISCV_BOOT_SPINWAIT:

• prompt: Spinwait booting method
• type: bool
• depends on: ( CONFIG_SMP ) && ( CONFIG_RISCV_SBI_V01 || CONFIG_RISCV_M_MODE )
• defined in arch/riscv/Kconfig
• found in Linux kernels: 5.17–5.19, 6.0–6.12, 6.13-rc+HEAD

Help text

This enables support for booting Linux via spinwait method. In the spinwait method, all cores randomly jump to Linux. One of the cores gets chosen via lottery and all other keep spinning on a percpu variable. This method cannot support CPU hotplug and sparse hartid scheme. It should be only enabled for M-mode Linux or platforms relying on older firmware without SBI HSM extension. All other platforms should rely on ordered booting via SBI HSM extension which gets chosen dynamically at runtime if the firmware supports it.

Since spinwait is incompatible with sparse hart IDs, it requires NR_CPUS be large enough to contain the physical hart ID of the first hart to enter Linux.

If unsure what to do here, say N.

Hardware

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The data is retrived from:

• Linux kernel
• Linux Kernel Driver DataBase (LKDDb)

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