Subject: [PATCHv3 4/5] arm64: add CPU_HOTPLUG infrastructure

From: [email-masked] (Santosh Shilimkar)
Date: Wed, 14 Aug 2013 15:24:38 -0400

On Wednesday 14 August 2013 12:20 PM, Mark Rutland wrote:
> This patch adds the basic infrastructure necessary to support
> CPU_HOTPLUG on arm64, based on the arm implementation. Actual hotplug
> support will depend on an implementation's smp_operations (e.g. PSCI).
> 
> Signed-off-by: Mark Rutland <[email-masked]>
> ---
>  arch/arm64/Kconfig           |  7 ++++
>  arch/arm64/include/asm/irq.h |  1 +
>  arch/arm64/include/asm/smp.h | 14 +++++++
>  arch/arm64/kernel/cputable.c |  2 +-
>  arch/arm64/kernel/irq.c      | 61 ++++++++++++++++++++++++++++
>  arch/arm64/kernel/process.c  |  7 ++++
>  arch/arm64/kernel/smp.c      | 97 ++++++++++++++++++++++++++++++++++++++++++++
>  7 files changed, 188 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 9737e97..5ce4ccb 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -158,6 +158,13 @@ config NR_CPUS
>  	default "8" if ARCH_XGENE
>  	default "4"
>  
> +config HOTPLUG_CPU
> +	bool "Support for hot-pluggable CPUs"
> +	depends on SMP
> +	help
> +	  Say Y here to experiment with turning CPUs off and on.  CPUs
> +	  can be controlled through /sys/devices/system/cpu.
> +
>  source kernel/Kconfig.preempt
>  
>  config HZ
> diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h
> index 0332fc0..e1f7ecd 100644
> --- a/arch/arm64/include/asm/irq.h
> +++ b/arch/arm64/include/asm/irq.h
> @@ -4,6 +4,7 @@
>  #include <asm-generic/irq.h>
>  
>  extern void (*handle_arch_irq)(struct pt_regs *);
> +extern void migrate_irqs(void);
>  extern void set_handle_irq(void (*handle_irq)(struct pt_regs *));
>  
>  #endif
> diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h
> index 831090a..d2ef02e 100644
> --- a/arch/arm64/include/asm/smp.h
> +++ b/arch/arm64/include/asm/smp.h
> @@ -67,6 +67,11 @@ extern void arch_send_call_function_ipi_mask(const struct cpumask *mask);
>  
>  struct device_node;
>  
> +extern int __cpu_disable(void);
> +
> +extern void __cpu_die(unsigned int cpu);
> +extern void cpu_die(void);
> +
>  /**
>   * struct smp_operations - Callback operations for hotplugging CPUs.
>   *
> @@ -80,6 +85,11 @@ struct device_node;
>   * @cpu_boot:	Boots a cpu into the kernel.
>   * @cpu_postboot: Optionally, perform any post-boot cleanup or necesary
>   *		synchronisation. Called from the cpu being booted.
> + * @cpu_disable: Prepares a cpu to die. May fail for some mechanism-specific
> + * 		reason, which will cause the hot unplug to be aborted. Called
> + * 		from the cpu to be killed.
> + * @cpu_die:	Makes the a leave the kernel. Must not fail. Called from the
> + *		cpu being killed.
>   */
>  struct smp_operations {
>  	const char	*name;
> @@ -87,6 +97,10 @@ struct smp_operations {
>  	int		(*cpu_prepare)(unsigned int);
>  	int		(*cpu_boot)(unsigned int);
>  	void		(*cpu_postboot)(void);
> +#ifdef CONFIG_HOTPLUG_CPU
> +	int  (*cpu_disable)(unsigned int cpu);
> +	void (*cpu_die)(unsigned int cpu);
> +#endif
>  };
>  
>  extern const struct smp_operations smp_spin_table_ops;
> diff --git a/arch/arm64/kernel/cputable.c b/arch/arm64/kernel/cputable.c
> index 63cfc4a..fd3993c 100644
> --- a/arch/arm64/kernel/cputable.c
> +++ b/arch/arm64/kernel/cputable.c
> @@ -22,7 +22,7 @@
>  
>  extern unsigned long __cpu_setup(void);
>  
> -struct cpu_info __initdata cpu_table[] = {
> +struct cpu_info cpu_table[] = {
>  	{
>  		.cpu_id_val	= 0x000f0000,
>  		.cpu_id_mask	= 0x000f0000,
> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
> index ecb3354..473e5db 100644
> --- a/arch/arm64/kernel/irq.c
> +++ b/arch/arm64/kernel/irq.c
> @@ -81,3 +81,64 @@ void __init init_IRQ(void)
>  	if (!handle_arch_irq)
>  		panic("No interrupt controller found.");
>  }
> +
> +#ifdef CONFIG_HOTPLUG_CPU
> +static bool migrate_one_irq(struct irq_desc *desc)
> +{
> +	struct irq_data *d = irq_desc_get_irq_data(desc);
> +	const struct cpumask *affinity = d->affinity;
> +	struct irq_chip *c;
> +	bool ret = false;
> +
> +	/*
> +	 * If this is a per-CPU interrupt, or the affinity does not
> +	 * include this CPU, then we have nothing to do.
> +	 */
> +	if (irqd_is_per_cpu(d) || !cpumask_test_cpu(smp_processor_id(), affinity))
> +		return false;
> +
> +	if (cpumask_any_and(affinity, cpu_online_mask) >= nr_cpu_ids) {
> +		affinity = cpu_online_mask;
> +		ret = true;
> +	}
> +
> +	c = irq_data_get_irq_chip(d);
> +	if (!c->irq_set_affinity)
> +		pr_debug("IRQ%u: unable to set affinity\n", d->irq);
> +	else if (c->irq_set_affinity(d, affinity, true) == IRQ_SET_MASK_OK && ret)
> +		cpumask_copy(d->affinity, affinity);
> +
> +	return ret;
> +}
> +
> +/*
> + * The current CPU has been marked offline.  Migrate IRQs off this CPU.
> + * If the affinity settings do not allow other CPUs, force them onto any
> + * available CPU.
> + *
> + * Note: we must iterate over all IRQs, whether they have an attached
> + * action structure or not, as we need to get chained interrupts too.
> + */
> +void migrate_irqs(void)
> +{
> +	unsigned int i;
> +	struct irq_desc *desc;
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +
> +	for_each_irq_desc(i, desc) {
> +		bool affinity_broken;
> +
> +		raw_spin_lock(&desc->lock);
> +		affinity_broken = migrate_one_irq(desc);
> +		raw_spin_unlock(&desc->lock);
> +
> +		if (affinity_broken)
> +			pr_warn_ratelimited("IRQ%u no longer affine to CPU%u\n",
> +					    i, smp_processor_id());
> +	}
> +
> +	local_irq_restore(flags);
> +}
> +#endif /* CONFIG_HOTPLUG_CPU */
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 57fb55c..19f17ec 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -102,6 +102,13 @@ void arch_cpu_idle(void)
>  	local_irq_enable();
>  }
>  
> +#ifdef CONFIG_HOTPLUG_CPU
> +void arch_cpu_idle_dead(void)
> +{
> +       cpu_die();
> +}
> +#endif
> +
>  void machine_shutdown(void)
>  {
>  #ifdef CONFIG_SMP
> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> index f6ce2ae..51c1acd 100644
> --- a/arch/arm64/kernel/smp.c
> +++ b/arch/arm64/kernel/smp.c
> @@ -168,6 +168,103 @@ asmlinkage void secondary_start_kernel(void)
>  	cpu_startup_entry(CPUHP_ONLINE);
>  }
>  
> +#ifdef CONFIG_HOTPLUG_CPU
> +static int op_cpu_disable(unsigned int cpu)
> +{
> +	/*
> +	 * If we don't have a cpu_die method, abort before we reach the point
> +	 * of no return. CPU0 may not have an smp_ops, so test for it.
> +	 */
> +	if (!smp_ops[cpu] || !smp_ops[cpu]->cpu_die)
> +		return -EOPNOTSUPP;
> +
> +	/*
> +	 * We may need to abort a hot unplug for some other mechanism-specific
> +	 * reason.
> +	 */
> +	if (smp_ops[cpu]->cpu_disable)
> +		return smp_ops[cpu]->cpu_disable(cpu);
> +
> +	return 0;
> +}
> +
> +/*
> + * __cpu_disable runs on the processor to be shutdown.
> + */
> +int __cpu_disable(void)
> +{
> +	unsigned int cpu = smp_processor_id();
> +	int ret;
> +
> +	ret = op_cpu_disable(cpu);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Take this CPU offline.  Once we clear this, we can't return,
> +	 * and we must not schedule until we're ready to give up the cpu.
> +	 */
> +	set_cpu_online(cpu, false);
> +
> +	/*
> +	 * OK - migrate IRQs away from this CPU
> +	 */
> +	migrate_irqs();
> +
> +	/*
> +	 * Remove this CPU from the vm mask set of all processes.
> +	 */
> +	clear_tasks_mm_cpumask(cpu);
> +
> +	return 0;
> +}
> +
> +static DECLARE_COMPLETION(cpu_died);
> +
> +/*
> + * called on the thread which is asking for a CPU to be shutdown -
> + * waits until shutdown has completed, or it is timed out.
> + */
> +void __cpu_die(unsigned int cpu)
> +{
> +	if (!wait_for_completion_timeout(&cpu_died, msecs_to_jiffies(5000))) {
> +		pr_crit("CPU%u: cpu didn't die\n", cpu);
> +		return;
> +	}
> +	pr_notice("CPU%u: shutdown\n", cpu);
> +}
> +
> +/*
> + * Called from the idle thread for the CPU which has been shutdown.
> + *
> + * Note that we disable IRQs here, but do not re-enable them
> + * before returning to the caller. This is also the behaviour
> + * of the other hotplug-cpu capable cores, so presumably coming
> + * out of idle fixes this.
> + */
> +void __ref cpu_die(void)
> +{
> +	unsigned int cpu = smp_processor_id();
> +
> +	idle_task_exit();
> +
> +	local_irq_disable();
> +	mb();
> +
> +	/* Tell __cpu_die() that this CPU is now safe to dispose of */
> +	complete(&cpu_died);
> +
> +	/*
> +	 * Actually shutdown the CPU. This must never fail. The specific hotplug
> +	 * mechanism must perform all required cache maintenance to ensure that
> +	 * no dirty lines are lost in the process of shutting down the CPU.
> +	 */
> +	smp_ops[cpu]->cpu_die(cpu);
> +
> +	BUG();
> +}
> +#endif
> +
>  void __init smp_cpus_done(unsigned int max_cpus)
>  {
>  	unsigned long bogosum = loops_per_jiffy * num_online_cpus();
> 
Above code looks like direct re-use from arm32 bit port.
I don't know whether its worth trouble to abstract but at least code
looks pretty same.

Other than the patch looks fine.
Acked-by: Santosh Shilimkar <[email-masked]>