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Date: Mon, 11 Feb 2013 12:09:58 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Rusty Russell <rusty@...tcorp.com.au>,
"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
Arjan van de Veen <arjan@...radead.org>,
Paul Turner <pjt@...gle.com>,
Richard Weinberger <rw@...utronix.de>,
Magnus Damm <magnus.damm@...il.com>
Subject: Re: [patch 07/40] cpu: hotplug: Convert to a state machine for the
control processor
On Thu, Jan 31, 2013 at 12:11:17PM -0000, Thomas Gleixner wrote:
> Move the split out steps into a callback array and let the cpu_up/down
> code iterate through the array functions. For now most of the
> callbacks are asymetric to resemble the current hotplug maze.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
> include/linux/cpu.h | 4 +
> include/linux/cpuhotplug.h | 16 ++++
> init/main.c | 15 ---
> kernel/cpu.c | 180 ++++++++++++++++++++++++++++++++++++---------
> kernel/smpboot.c | 6 +
> kernel/smpboot.h | 4 -
> 6 files changed, 173 insertions(+), 52 deletions(-)
>
> Index: linux-2.6/include/linux/cpu.h
> ===================================================================
> --- linux-2.6.orig/include/linux/cpu.h
> +++ linux-2.6/include/linux/cpu.h
> @@ -26,6 +26,9 @@ struct cpu {
> struct device dev;
> };
>
> +extern void boot_cpu_init(void);
> +extern void boot_cpu_state_init(void);
> +
> extern int register_cpu(struct cpu *cpu, int num);
> extern struct device *get_cpu_device(unsigned cpu);
> extern bool cpu_is_hotpluggable(unsigned cpu);
> @@ -112,6 +115,7 @@ enum {
>
>
> #ifdef CONFIG_SMP
> +extern bool cpuhp_tasks_frozen;
> /* Need to know about CPUs going up/down? */
> #if defined(CONFIG_HOTPLUG_CPU) || !defined(MODULE)
> #define cpu_notifier(fn, pri) { \
> Index: linux-2.6/include/linux/cpuhotplug.h
> ===================================================================
> --- /dev/null
> +++ linux-2.6/include/linux/cpuhotplug.h
> @@ -0,0 +1,16 @@
> +#ifndef __CPUHOTPLUG_H
> +#define __CPUHOTPLUG_H
> +
> +enum cpuhp_states {
> + CPUHP_OFFLINE,
> + CPUHP_CREATE_THREADS,
> + CPUHP_NOTIFY_PREPARE,
> + CPUHP_NOTIFY_DEAD,
> + CPUHP_BRINGUP_CPU,
> + CPUHP_TEARDOWN_CPU,
> + CPUHP_PERCPU_THREADS,
> + CPUHP_NOTIFY_ONLINE,
> + CPUHP_NOTIFY_DOWN_PREPARE,
> + CPUHP_MAX,
> +};
> +#endif
> Index: linux-2.6/init/main.c
> ===================================================================
> --- linux-2.6.orig/init/main.c
> +++ linux-2.6/init/main.c
> @@ -424,20 +424,6 @@ void __init parse_early_param(void)
> done = 1;
> }
>
> -/*
> - * Activate the first processor.
> - */
> -
> -static void __init boot_cpu_init(void)
> -{
> - int cpu = smp_processor_id();
> - /* Mark the boot cpu "present", "online" etc for SMP and UP case */
> - set_cpu_online(cpu, true);
> - set_cpu_active(cpu, true);
> - set_cpu_present(cpu, true);
> - set_cpu_possible(cpu, true);
> -}
> -
> void __init __weak smp_setup_processor_id(void)
> {
> }
> @@ -502,6 +488,7 @@ asmlinkage void __init start_kernel(void
> setup_command_line(command_line);
> setup_nr_cpu_ids();
> setup_per_cpu_areas();
> + boot_cpu_state_init();
> smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
>
> build_all_zonelists(NULL, NULL);
> Index: linux-2.6/kernel/cpu.c
> ===================================================================
> --- linux-2.6.orig/kernel/cpu.c
> +++ linux-2.6/kernel/cpu.c
> @@ -19,13 +19,24 @@
> #include <linux/mutex.h>
> #include <linux/gfp.h>
> #include <linux/suspend.h>
> +#include <linux/cpuhotplug.h>
>
> #include "smpboot.h"
>
> +/* CPU state */
> +static DEFINE_PER_CPU(enum cpuhp_states, cpuhp_state);
> +
> +struct cpuhp_step {
> + int (*startup)(unsigned int cpu);
> + int (*teardown)(unsigned int cpu);
> +};
> +
> +static struct cpuhp_step cpuhp_bp_states[];
> +
> #ifdef CONFIG_SMP
> /* Serializes the updates to cpu_online_mask, cpu_present_mask */
> static DEFINE_MUTEX(cpu_add_remove_lock);
> -static bool cpuhp_tasks_frozen;
> +bool cpuhp_tasks_frozen;
>
> /*
> * The following two API's must be used when attempting
> @@ -310,13 +321,10 @@ static int __ref take_cpu_down(void *_pa
>
> static int takedown_cpu(unsigned int cpu)
> {
> - int err;
> + int err = __stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
>
> - smpboot_park_threads(cpu);
> - err = __stop_machine(take_cpu_down, NULL, cpumask_of(cpu));
> if (err) {
> /* CPU didn't die: tell everyone. Can't complain. */
> - smpboot_unpark_threads(cpu);
> cpu_notify_nofail(CPU_DOWN_FAILED, cpu);
> return err;
> }
> @@ -345,10 +353,32 @@ static int notify_dead(unsigned int cpu)
> return 0;
> }
>
> +#else
> +#define notify_down_prepare NULL
> +#define takedown_cpu NULL
> +#define notify_dead NULL
> +#endif
> +
> +#ifdef CONFIG_HOTPLUG_CPU
> +static void undo_cpu_down(unsigned int cpu, int step)
> +{
> + while (step++ < CPUHP_MAX) {
> + /*
> + * Transitional check. Will be removed when we have a
> + * fully symetric mechanism
> + */
> + if (!cpuhp_bp_states[step].teardown)
> + continue;
> +
> + if (cpuhp_bp_states[step].startup)
> + cpuhp_bp_states[step].startup(cpu);
> + }
> +}
> +
> /* Requires cpu_add_remove_lock to be held */
> static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
> {
> - int err;
> + int ret = 0, step;
>
> if (num_online_cpus() == 1)
> return -EBUSY;
> @@ -360,20 +390,23 @@ static int __ref _cpu_down(unsigned int
>
> cpuhp_tasks_frozen = tasks_frozen;
>
> - err = notify_down_prepare(cpu);
> - if (err)
> - goto out_release;
> - err = takedown_cpu(cpu);
> - if (err)
> - goto out_release;
> -
> - notify_dead(cpu);
> + for (step = per_cpu(cpuhp_state, cpu); step > 0; step--) {
> + if (cpuhp_bp_states[step].teardown) {
> + ret = cpuhp_bp_states[step].teardown(cpu);
> + if (ret) {
> + undo_cpu_down(cpu, step + 1);
> + step = CPUHP_MAX;
> + break;
> + }
> + }
> + }
> + /* Store the current cpu state */
> + per_cpu(cpuhp_state, cpu) = step;
>
> -out_release:
> cpu_hotplug_done();
> - if (!err)
> + if (!ret)
> cpu_notify_nofail(CPU_POST_DEAD, cpu);
> - return err;
> + return ret;
> }
>
> int __ref cpu_down(unsigned int cpu)
> @@ -396,11 +429,25 @@ out:
> EXPORT_SYMBOL(cpu_down);
> #endif /*CONFIG_HOTPLUG_CPU*/
>
> +static void undo_cpu_up(unsigned int cpu, int step)
> +{
> + while (step--) {
> + /*
> + * Transitional check. Will be removed when we have a
> + * fully symetric mechanism
> + */
> + if (!cpuhp_bp_states[step].startup)
> + continue;
> + if (cpuhp_bp_states[step].teardown)
> + cpuhp_bp_states[step].teardown(cpu);
> + }
> +}
> +
> /* Requires cpu_add_remove_lock to be held */
> static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
> {
> + int ret = 0, step;
> struct task_struct *idle;
> - int ret;
>
> cpu_hotplug_begin();
>
> @@ -409,6 +456,7 @@ static int __cpuinit _cpu_up(unsigned in
> goto out;
> }
>
> + /* Let it fail before we try to bring the cpu up */
> idle = idle_thread_get(cpu);
> if (IS_ERR(idle)) {
> ret = PTR_ERR(idle);
> @@ -417,24 +465,20 @@ static int __cpuinit _cpu_up(unsigned in
>
> cpuhp_tasks_frozen = tasks_frozen;
>
> - ret = smpboot_create_threads(cpu);
> - if (ret)
> - goto out;
> -
> - ret = notify_prepare(cpu);
> - if (ret)
> - goto out;
> -
> - ret = bringup_cpu(cpu);
> - if (ret)
> - goto out;
> -
> - /* Wake the per cpu threads */
> - smpboot_unpark_threads(cpu);
> - notify_online(cpu);
> + for (step = per_cpu(cpuhp_state, cpu); step < CPUHP_MAX; step++) {
> + if (cpuhp_bp_states[step].startup) {
> + ret = cpuhp_bp_states[step].startup(cpu);
> + if (ret) {
> + undo_cpu_up(cpu, step - 1);
> + step = 0;
> + break;
> + }
> + }
> + }
> + /* Store the current cpu state */
> + per_cpu(cpuhp_state, cpu) = step;
> out:
> cpu_hotplug_done();
> -
> return ret;
> }
>
> @@ -674,6 +718,52 @@ void __cpuinit notify_cpu_starting(unsig
>
> #endif /* CONFIG_SMP */
>
> +/* Boot processor state steps */
> +static struct cpuhp_step cpuhp_bp_states[] = {
> + [CPUHP_OFFLINE] = {
> + .startup = NULL,
> + .teardown = NULL,
> + },
> +#ifdef CONFIG_SMP
> + [CPUHP_CREATE_THREADS] = {
> + .startup = smpboot_create_threads,
> + .teardown = NULL,
> + },
> + [CPUHP_NOTIFY_PREPARE] = {
> + .startup = notify_prepare,
> + .teardown = NULL,
> + },
> + [CPUHP_NOTIFY_DEAD] = {
> + .startup = NULL,
> + .teardown = notify_dead,
> + },
> + [CPUHP_BRINGUP_CPU] = {
> + .startup = bringup_cpu,
> + .teardown = NULL,
> + },
> + [CPUHP_TEARDOWN_CPU] = {
> + .startup = NULL,
> + .teardown = takedown_cpu,
> + },
> + [CPUHP_PERCPU_THREADS] = {
> + .startup = smpboot_unpark_threads,
> + .teardown = smpboot_park_threads,
> + },
> + [CPUHP_NOTIFY_ONLINE] = {
> + .startup = notify_online,
> + .teardown = NULL,
> + },
> + [CPUHP_NOTIFY_DOWN_PREPARE] = {
> + .startup = NULL,
> + .teardown = notify_down_prepare,
> + },
> +#endif
> + [CPUHP_MAX] = {
> + .startup = NULL,
> + .teardown = NULL,
> + },
> +};
> +
> /*
> * cpu_bit_bitmap[] is a special, "compressed" data structure that
> * represents all NR_CPUS bits binary values of 1<<nr.
> @@ -769,3 +859,25 @@ void init_cpu_online(const struct cpumas
> {
> cpumask_copy(to_cpumask(cpu_online_bits), src);
> }
> +
> +/*
> + * Activate the first processor.
> + */
> +void __init boot_cpu_init(void)
> +{
> + int cpu = smp_processor_id();
> +
> + /* Mark the boot cpu "present", "online" etc for SMP and UP case */
> + set_cpu_online(cpu, true);
> + set_cpu_active(cpu, true);
> + set_cpu_present(cpu, true);
> + set_cpu_possible(cpu, true);
> +}
> +
> +/*
> + * Must be called _AFTER_ setting up the per_cpu areas
> + */
> +void __init boot_cpu_state_init(void)
> +{
> + per_cpu(cpuhp_state, smp_processor_id()) = CPUHP_MAX;
> +}
> Index: linux-2.6/kernel/smpboot.c
> ===================================================================
> --- linux-2.6.orig/kernel/smpboot.c
> +++ linux-2.6/kernel/smpboot.c
> @@ -212,7 +212,7 @@ static void smpboot_unpark_thread(struct
> kthread_unpark(tsk);
> }
>
> -void smpboot_unpark_threads(unsigned int cpu)
> +int smpboot_unpark_threads(unsigned int cpu)
> {
> struct smp_hotplug_thread *cur;
>
> @@ -220,6 +220,7 @@ void smpboot_unpark_threads(unsigned int
> list_for_each_entry(cur, &hotplug_threads, list)
> smpboot_unpark_thread(cur, cpu);
> mutex_unlock(&smpboot_threads_lock);
> + return 0;
> }
>
> static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
> @@ -230,7 +231,7 @@ static void smpboot_park_thread(struct s
> kthread_park(tsk);
> }
>
> -void smpboot_park_threads(unsigned int cpu)
> +int smpboot_park_threads(unsigned int cpu)
> {
> struct smp_hotplug_thread *cur;
>
> @@ -238,6 +239,7 @@ void smpboot_park_threads(unsigned int c
> list_for_each_entry_reverse(cur, &hotplug_threads, list)
> smpboot_park_thread(cur, cpu);
> mutex_unlock(&smpboot_threads_lock);
> + return 0;
> }
>
> static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
> Index: linux-2.6/kernel/smpboot.h
> ===================================================================
> --- linux-2.6.orig/kernel/smpboot.h
> +++ linux-2.6/kernel/smpboot.h
> @@ -14,7 +14,7 @@ static inline void idle_threads_init(voi
> #endif
>
> int smpboot_create_threads(unsigned int cpu);
> -void smpboot_park_threads(unsigned int cpu);
> -void smpboot_unpark_threads(unsigned int cpu);
> +int smpboot_park_threads(unsigned int cpu);
> +int smpboot_unpark_threads(unsigned int cpu);
>
> #endif
>
>
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