A kernel built with RCU_NOCB_CPU_ALL build time option will offload callbacks from all CPUs. The user cannot override this behavior without recompiling the kernel with the RCU_NOCB_CPU_ALL option turned off.
This commit allows the user to override the build-time option by using the rcu_nocbs= boot time option without needing to recompile the kernel. Please note that this is how NO_HZ_FULL_ALL build time option works and this commit makes it work similar to that. Signed-off-by: Pranith Kumar <[email protected]> --- init/Kconfig | 14 +++++++------- kernel/rcu/tree_plugin.h | 8 ++++---- 2 files changed, 11 insertions(+), 11 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 41066e4..7d363a4 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -768,13 +768,13 @@ config RCU_NOCB_CPU_ALL bool "All CPUs are build_forced no-CBs CPUs" depends on RCU_NOCB_CPU help - This option forces all CPUs to be no-CBs CPUs. The rcu_nocbs= - boot parameter will be ignored. All CPUs' RCU callbacks will - be executed in the context of per-CPU rcuo kthreads created for - this purpose. Assuming that the kthreads whose names start with - "rcuo" are bound to "housekeeping" CPUs, this reduces OS jitter - on the remaining CPUs, but might decrease memory locality during - RCU-callback invocation, thus potentially degrading throughput. + If the user doesn't pass the rcu_nocbs= boot option, force all CPUs + to be no-CBs CPUs. All CPUs' RCU callbacks will be executed in the + context of per-CPU rcuo kthreads created for this purpose. Assuming + that the kthreads whose names start with "rcuo" are bound to + "housekeeping" CPUs, this reduces OS jitter on the remaining CPUs, but + might decrease memory locality during RCU-callback invocation, thus + potentially degrading throughput. Select this if all CPUs need to be no-CBs CPUs for real-time or energy-efficiency reasons. diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index a2113f6..b97a939 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -92,15 +92,15 @@ static void __init rcu_bootup_announce_oddness(void) if (!have_rcu_nocb_mask) { zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL); have_rcu_nocb_mask = true; +#ifdef CONFIG_RCU_NOCB_CPU_ALL + pr_info("\tOffload RCU callbacks from all CPUs\n"); + cpumask_copy(rcu_nocb_mask, cpu_possible_mask); +#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ } #ifdef CONFIG_RCU_NOCB_CPU_ZERO pr_info("\tOffload RCU callbacks from CPU 0\n"); cpumask_set_cpu(0, rcu_nocb_mask); #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ -#ifdef CONFIG_RCU_NOCB_CPU_ALL - pr_info("\tOffload RCU callbacks from all CPUs\n"); - cpumask_copy(rcu_nocb_mask, cpu_possible_mask); -#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ if (have_rcu_nocb_mask) { if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
