From: Mark Rutland mark.rutland@arm.com
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@arm.com --- 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 db8ad10..e285ba1 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -183,6 +183,13 @@ 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 2a7a649..b05026c 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 a30ac03..f074292 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -171,6 +171,103 @@ 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();