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Commit 911af505 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

rcu: Provide compile-time control for no-CBs CPUs 



Currently, the only way to specify no-CBs CPUs is via the rcu_nocbs
kernel command-line parameter.  This is inconvenient in some cases,
particularly for randconfig testing, so this commit adds a new set of
kernel configuration parameters.  CONFIG_RCU_NOCB_CPU_NONE (the default)
retains the old behavior, CONFIG_RCU_NOCB_CPU_ZERO offloads callback
processing from CPU 0 (along with any other CPUs specified by the
rcu_nocbs boot-time parameter), and CONFIG_RCU_NOCB_CPU_ALL offloads
callback processing from all CPUs.

Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 34ed6246

init/Kconfig

+39 −0
Original line number Diff line number Diff line
@@ -676,6 +676,45 @@ config RCU_NOCB_CPU 
	  Say Y here if you want to help to debug reduced OS jitter.

	  Say N here if you are unsure.



choice

	prompt "Build-forced no-CBs CPUs"

	default RCU_NOCB_CPU_NONE

	help

	  This option allows no-CBs CPUs to be specified at build time.

	  Additional no-CBs CPUs may be specified by the rcu_nocbs=

	  boot parameter.



config RCU_NOCB_CPU_NONE

	bool "No build_forced no-CBs CPUs"

	depends on RCU_NOCB_CPU

	help

	  This option does not force any of the CPUs to be no-CBs CPUs.

	  Only CPUs designated by the rcu_nocbs= boot parameter will be

	  no-CBs CPUs.



config RCU_NOCB_CPU_ZERO

	bool "CPU 0 is a build_forced no-CBs CPU"

	depends on RCU_NOCB_CPU

	help

	  This option forces CPU 0 to be a no-CBs CPU.  Additional CPUs

	  may be designated as no-CBs CPUs using the rcu_nocbs= boot

	  parameter will be no-CBs CPUs.



	  Select this if CPU 0 needs to be a no-CBs CPU for real-time

	  or energy-efficiency reasons.



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.



	  Select this if all CPUs need to be no-CBs CPUs for real-time

	  or energy-efficiency reasons.



endchoice



endmenu # "RCU Subsystem"



config IKCONFIG

kernel/rcutree_plugin.h

+14 −0
Original line number Diff line number Diff line
@@ -85,6 +85,20 @@ static void __init rcu_bootup_announce_oddness(void) 
	if (nr_cpu_ids != NR_CPUS)

		printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);

#ifdef CONFIG_RCU_NOCB_CPU

#ifndef CONFIG_RCU_NOCB_CPU_NONE

	if (!have_rcu_nocb_mask) {

		alloc_bootmem_cpumask_var(&rcu_nocb_mask);

		have_rcu_nocb_mask = true;

	}

#ifdef CONFIG_RCU_NOCB_CPU_ZERO

	pr_info("\tExperimental no-CBs 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("\tExperimental no-CBs for all CPUs\n");

	cpumask_setall(rcu_nocb_mask);

#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */

#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */

	if (have_rcu_nocb_mask) {

		cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);

		pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf);