CONFIG_RCU_FAST_NO_HZ: Accelerate last non-dyntick-idle CPU's grace periods

General informations

The Linux kernel configuration item CONFIG_RCU_FAST_NO_HZ has multiple definitions:

Accelerate last non-dyntick-idle CPU's grace periods found in kernel/rcu/Kconfig

The configuration item CONFIG_RCU_FAST_NO_HZ:

• prompt: Accelerate last non-dyntick-idle CPU's grace periods
• type: bool
• depends on: CONFIG_NO_HZ_COMMON && CONFIG_SMP && CONFIG_RCU_EXPERT
• defined in kernel/rcu/Kconfig
• found in Linux kernels: 4.13–4.20, 5.0–5.16

Help text

This option permits CPUs to enter dynticks-idle state even if they have RCU callbacks queued, and prevents RCU from waking these CPUs up more than roughly once every four jiffies (by default, you can adjust this using the rcutree.rcu_idle_gp_delay parameter), thus improving energy efficiency. On the other hand, this option increases the duration of RCU grace periods, for example, slowing down synchronize_rcu().

Say Y if energy efficiency is critically important, and you don't care about increased grace-period durations.

Say N if you are unsure.

Accelerate last non-dyntick-idle CPU's grace periods found in init/Kconfig

The configuration item CONFIG_RCU_FAST_NO_HZ:

• prompt: Accelerate last non-dyntick-idle CPU's grace periods
• type: bool
• depends on: CONFIG_NO_HZ_COMMON && CONFIG_SMP && CONFIG_RCU_EXPERT
• defined in init/Kconfig
• found in Linux kernels: 2.6.34–2.6.39, 3.0–3.19, 4.0–4.12

Help text

This option permits CPUs to enter dynticks-idle state even if they have RCU callbacks queued, and prevents RCU from waking these CPUs up more than roughly once every four jiffies (by default, you can adjust this using the rcutree.rcu_idle_gp_delay parameter), thus improving energy efficiency. On the other hand, this option increases the duration of RCU grace periods, for example, slowing down synchronize_rcu().

Say Y if energy efficiency is critically important, and you don't care about increased grace-period durations.

Say N if you are unsure.

Hardware

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Sources

This page is automaticly generated with free (libre, open) software lkddb(see lkddb-sources).

The data is retrived from:

• Linux kernel
• Linux Kernel Driver DataBase (LKDDb)

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