[PATCHv3 4/5] arm64: add CPU_HOTPLUG infrastructure
Nicolas Pitre
nicolas.pitre at linaro.org
Wed Aug 14 13:53:07 EDT 2013
On Wed, 14 Aug 2013, 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 <mark.rutland at arm.com>
Acked-by: Nicolas Pitre <nico at linaro.org>
> ---
> 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();
> --
> 1.8.1.1
>
More information about the linux-arm-kernel
mailing list