[ARM SMP] Add hotplug CPU infrastructure

This patch adds the infrastructure to support hotplug CPU on ARM
platforms.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index dc6d834..6b12d71 100644 (file)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -349,6 +349,13 @@ config NR_CPUS
        depends on SMP
        default "4"
 
+config HOTPLUG_CPU
+       bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
+       depends on SMP && HOTPLUG && EXPERIMENTAL
+       help
+         Say Y here to experiment with turning CPUs off and on.  CPUs
+         can be controlled through /sys/devices/system/cpu.
+
 config PREEMPT
        bool "Preemptible Kernel (EXPERIMENTAL)"
        depends on EXPERIMENTAL

diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 3284118..9def440 100644 (file)
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -1050,3 +1050,34 @@ static int __init noirqdebug_setup(char *str)
 }
 
 __setup("noirqdebug", noirqdebug_setup);
+
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * The 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.
+ */
+void migrate_irqs(void)
+{
+       unsigned int i, cpu = smp_processor_id();
+
+       for (i = 0; i < NR_IRQS; i++) {
+               struct irqdesc *desc = irq_desc + i;
+
+               if (desc->cpu == cpu) {
+                       unsigned int newcpu = any_online_cpu(desc->affinity);
+
+                       if (newcpu == NR_CPUS) {
+                               if (printk_ratelimit())
+                                       printk(KERN_INFO "IRQ%u no longer affine to CPU%u\n",
+                                              i, cpu);
+
+                               cpus_setall(desc->affinity);
+                               newcpu = any_online_cpu(desc->affinity);
+                       }
+
+                       route_irq(desc, i, newcpu);
+               }
+       }
+}
+#endif /* CONFIG_HOTPLUG_CPU */

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 409db6d..ba29827 100644 (file)
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -26,6 +26,7 @@
 #include <linux/interrupt.h>
 #include <linux/kallsyms.h>
 #include <linux/init.h>
+#include <linux/cpu.h>
 
 #include <asm/system.h>
 #include <asm/io.h>
@@ -105,6 +106,14 @@ void cpu_idle(void)
        /* endless idle loop with no priority at all */
        while (1) {
                void (*idle)(void) = pm_idle;
+
+#ifdef CONFIG_HOTPLUG_CPU
+               if (cpu_is_offline(smp_processor_id())) {
+                       leds_event(led_idle_start);
+                       cpu_die();
+               }
+#endif
+
                if (!idle)
                        idle = default_idle;
                preempt_disable();

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index b40915d..edb5a40 100644 (file)
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -159,6 +159,91 @@ int __cpuinit __cpu_up(unsigned int cpu)
        return ret;
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * __cpu_disable runs on the processor to be shutdown.
+ */
+int __cpuexit __cpu_disable(void)
+{
+       unsigned int cpu = smp_processor_id();
+       struct task_struct *p;
+       int ret;
+
+       ret = mach_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.
+        */
+       cpu_clear(cpu, cpu_online_map);
+
+       /*
+        * OK - migrate IRQs away from this CPU
+        */
+       migrate_irqs();
+
+       /*
+        * Flush user cache and TLB mappings, and then remove this CPU
+        * from the vm mask set of all processes.
+        */
+       flush_cache_all();
+       local_flush_tlb_all();
+
+       read_lock(&tasklist_lock);
+       for_each_process(p) {
+               if (p->mm)
+                       cpu_clear(cpu, p->mm->cpu_vm_mask);
+       }
+       read_unlock(&tasklist_lock);
+
+       return 0;
+}
+
+/*
+ * called on the thread which is asking for a CPU to be shutdown -
+ * waits until shutdown has completed, or it is timed out.
+ */
+void __cpuexit __cpu_die(unsigned int cpu)
+{
+       if (!platform_cpu_kill(cpu))
+               printk("CPU%u: unable to kill\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 __cpuexit cpu_die(void)
+{
+       unsigned int cpu = smp_processor_id();
+
+       local_irq_disable();
+       idle_task_exit();
+
+       /*
+        * actual CPU shutdown procedure is at least platform (if not
+        * CPU) specific
+        */
+       platform_cpu_die(cpu);
+
+       /*
+        * Do not return to the idle loop - jump back to the secondary
+        * cpu initialisation.  There's some initialisation which needs
+        * to be repeated to undo the effects of taking the CPU offline.
+        */
+       __asm__("mov    sp, %0\n"
+       "       b       secondary_start_kernel"
+               :
+               : "r" ((void *)current->thread_info + THREAD_SIZE - 8));
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
 /*
  * This is the secondary CPU boot entry.  We're using this CPUs
  * idle thread stack, but a set of temporary page tables.

diff --git a/include/asm-arm/irq.h b/include/asm-arm/irq.h
index f97912f..59975ee 100644 (file)
--- a/include/asm-arm/irq.h
+++ b/include/asm-arm/irq.h
@@ -47,5 +47,6 @@ struct irqaction;
 struct pt_regs;
 int handle_IRQ_event(unsigned int, struct pt_regs *, struct irqaction *);
 
+extern void migrate_irqs(void);
 #endif
 

diff --git a/include/asm-arm/smp.h b/include/asm-arm/smp.h
index dbb4d85..551cd3c 100644 (file)
--- a/include/asm-arm/smp.h
+++ b/include/asm-arm/smp.h
@@ -66,4 +66,14 @@ struct secondary_data {
 };
 extern struct secondary_data secondary_data;
 
+extern int __cpu_disable(void);
+extern int mach_cpu_disable(unsigned int cpu);
+
+extern void __cpu_die(unsigned int cpu);
+extern void cpu_die(void);
+
+extern void platform_cpu_die(unsigned int cpu);
+extern int platform_cpu_kill(unsigned int cpu);
+extern void platform_cpu_enable(unsigned int cpu);
+
 #endif /* ifndef __ASM_ARM_SMP_H */