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Date: Fri, 8 Feb 2013 16:39:00 -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 03/40] stop_machine: Use smpboot threads
On Thu, Jan 31, 2013 at 12:11:14PM -0000, Thomas Gleixner wrote:
> Use the smpboot thread infrastructure. Mark the stopper thread
> selfparking and park it after it has finished the take_cpu_down()
> work.
>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
One grammar nit, other than that:
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
> kernel/cpu.c | 2
> kernel/stop_machine.c | 134 ++++++++++++++++++--------------------------------
> 2 files changed, 51 insertions(+), 85 deletions(-)
>
> Index: linux-2.6/kernel/cpu.c
> ===================================================================
> --- linux-2.6.orig/kernel/cpu.c
> +++ linux-2.6/kernel/cpu.c
> @@ -254,6 +254,8 @@ static int __ref take_cpu_down(void *_pa
> return err;
>
> cpu_notify(CPU_DYING | param->mod, param->hcpu);
> + /* Park the stopper thread */
> + kthread_park(current);
> return 0;
> }
>
> Index: linux-2.6/kernel/stop_machine.c
> ===================================================================
> --- linux-2.6.orig/kernel/stop_machine.c
> +++ linux-2.6/kernel/stop_machine.c
> @@ -18,7 +18,7 @@
> #include <linux/stop_machine.h>
> #include <linux/interrupt.h>
> #include <linux/kallsyms.h>
> -
> +#include <linux/smpboot.h>
> #include <linux/atomic.h>
>
> /*
> @@ -245,20 +245,25 @@ int try_stop_cpus(const struct cpumask *
> return ret;
> }
>
> -static int cpu_stopper_thread(void *data)
> +static int cpu_stop_should_run(unsigned int cpu)
> +{
> + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
> + unsigned long flags;
> + int run;
> +
> + spin_lock_irqsave(&stopper->lock, flags);
> + run = !list_empty(&stopper->works);
> + spin_unlock_irqrestore(&stopper->lock, flags);
> + return run;
> +}
> +
> +static void cpu_stopper_thread(unsigned int cpu)
> {
> - struct cpu_stopper *stopper = data;
> + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
> struct cpu_stop_work *work;
> int ret;
>
> repeat:
> - set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
> -
> - if (kthread_should_stop()) {
> - __set_current_state(TASK_RUNNING);
> - return 0;
> - }
> -
> work = NULL;
> spin_lock_irq(&stopper->lock);
> if (!list_empty(&stopper->works)) {
> @@ -274,8 +279,6 @@ repeat:
> struct cpu_stop_done *done = work->done;
> char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
>
> - __set_current_state(TASK_RUNNING);
> -
> /* cpu stop callbacks are not allowed to sleep */
> preempt_disable();
>
> @@ -291,87 +294,55 @@ repeat:
> ksym_buf), arg);
>
> cpu_stop_signal_done(done, true);
> - } else
> - schedule();
> -
> - goto repeat;
> + goto repeat;
> + }
> }
>
> extern void sched_set_stop_task(int cpu, struct task_struct *stop);
>
> -/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
> -static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
> - unsigned long action, void *hcpu)
> +static void cpu_stop_create(unsigned int cpu)
> +{
> + sched_set_stop_task(cpu, per_cpu(cpu_stopper_task, cpu));
> +}
> +
> +static void cpu_stop_park(unsigned int cpu)
> {
> - unsigned int cpu = (unsigned long)hcpu;
> struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
> - struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
> + struct cpu_stop_work *work;
> + unsigned long flags;
>
> - switch (action & ~CPU_TASKS_FROZEN) {
> - case CPU_UP_PREPARE:
> - BUG_ON(p || stopper->enabled || !list_empty(&stopper->works));
> - p = kthread_create_on_node(cpu_stopper_thread,
> - stopper,
> - cpu_to_node(cpu),
> - "migration/%d", cpu);
> - if (IS_ERR(p))
> - return notifier_from_errno(PTR_ERR(p));
> - get_task_struct(p);
> - kthread_bind(p, cpu);
> - sched_set_stop_task(cpu, p);
> - per_cpu(cpu_stopper_task, cpu) = p;
> - break;
> + /* drain remaining works */
s/works/work/
> + spin_lock_irqsave(&stopper->lock, flags);
> + list_for_each_entry(work, &stopper->works, list)
> + cpu_stop_signal_done(work->done, false);
> + stopper->enabled = false;
> + spin_unlock_irqrestore(&stopper->lock, flags);
> +}
>
> - case CPU_ONLINE:
> - /* strictly unnecessary, as first user will wake it */
> - wake_up_process(p);
> - /* mark enabled */
> - spin_lock_irq(&stopper->lock);
> - stopper->enabled = true;
> - spin_unlock_irq(&stopper->lock);
> - break;
> -
> -#ifdef CONFIG_HOTPLUG_CPU
> - case CPU_UP_CANCELED:
> - case CPU_POST_DEAD:
> - {
> - struct cpu_stop_work *work;
> -
> - sched_set_stop_task(cpu, NULL);
> - /* kill the stopper */
> - kthread_stop(p);
> - /* drain remaining works */
> - spin_lock_irq(&stopper->lock);
> - list_for_each_entry(work, &stopper->works, list)
> - cpu_stop_signal_done(work->done, false);
> - stopper->enabled = false;
> - spin_unlock_irq(&stopper->lock);
> - /* release the stopper */
> - put_task_struct(p);
> - per_cpu(cpu_stopper_task, cpu) = NULL;
> - break;
> - }
> -#endif
> - }
> +static void cpu_stop_unpark(unsigned int cpu)
> +{
> + struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
>
> - return NOTIFY_OK;
> + spin_lock_irq(&stopper->lock);
> + stopper->enabled = true;
> + spin_unlock_irq(&stopper->lock);
> }
>
> -/*
> - * Give it a higher priority so that cpu stopper is available to other
> - * cpu notifiers. It currently shares the same priority as sched
> - * migration_notifier.
> - */
> -static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
> - .notifier_call = cpu_stop_cpu_callback,
> - .priority = 10,
> +static struct smp_hotplug_thread cpu_stop_threads = {
> + .store = &cpu_stopper_task,
> + .thread_should_run = cpu_stop_should_run,
> + .thread_fn = cpu_stopper_thread,
> + .thread_comm = "migration/%u",
> + .create = cpu_stop_create,
> + .setup = cpu_stop_unpark,
> + .park = cpu_stop_park,
> + .unpark = cpu_stop_unpark,
> + .selfparking = true,
> };
>
> static int __init cpu_stop_init(void)
> {
> - void *bcpu = (void *)(long)smp_processor_id();
> unsigned int cpu;
> - int err;
>
> for_each_possible_cpu(cpu) {
> struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
> @@ -380,15 +351,8 @@ static int __init cpu_stop_init(void)
> INIT_LIST_HEAD(&stopper->works);
> }
>
> - /* start one for the boot cpu */
> - err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
> - bcpu);
> - BUG_ON(err != NOTIFY_OK);
> - cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
> - register_cpu_notifier(&cpu_stop_cpu_notifier);
> -
> + BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
> stop_machine_initialized = true;
> -
> return 0;
> }
> early_initcall(cpu_stop_init);
>
>
--
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