softirq: Add support for triggering softirq work on softirqs.

This is basically a genericization of Jens Axboe's block layer
remote softirq changes.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 153 insertions, 1 deletions

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 54b3623434ec..35a61dc60d51 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -11,6 +11,8 @@
 #include <linux/hardirq.h>
 #include <linux/sched.h>
 #include <linux/irqflags.h>
+#include <linux/smp.h>
+#include <linux/percpu.h>
 #include <asm/atomic.h>
 #include <asm/ptrace.h>
 #include <asm/system.h>
@@ -273,6 +275,25 @@ extern void softirq_init(void);
 extern void raise_softirq_irqoff(unsigned int nr);
 extern void raise_softirq(unsigned int nr);
 
+/* This is the worklist that queues up per-cpu softirq work.
+ *
+ * send_remote_sendirq() adds work to these lists, and
+ * the softirq handler itself dequeues from them.  The queues
+ * are protected by disabling local cpu interrupts and they must
+ * only be accessed by the local cpu that they are for.
+ */
+DECLARE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
+
+/* Try to send a softirq to a remote cpu.  If this cannot be done, the
+ * work will be queued to the local cpu.
+ */
+extern void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq);
+
+/* Like send_remote_softirq(), but the caller must disable local cpu interrupts
+ * and compute the current cpu, passed in as 'this_cpu'.
+ */
+extern void __send_remote_softirq(struct call_single_data *cp, int cpu,
+                                  int this_cpu, int softirq);
 
 /* Tasklets --- multithreaded analogue of BHs.
 
diff --git a/include/linux/smp.h b/include/linux/smp.h
index 66484d4a8459..2e4d58b26c06 100644
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -7,6 +7,7 @@
  */
 
 #include <linux/errno.h>
+#include <linux/types.h>
 #include <linux/list.h>
 #include <linux/cpumask.h>
 
@@ -16,7 +17,8 @@ struct call_single_data {
         struct list_head list;
         void (*func) (void *info);
         void *info;
-        unsigned int flags;
+        u16 flags;
+        u16 priv;
 };
 
 #ifdef CONFIG_SMP
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 37d67aa2d56f..83ba21a13bd4 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -6,6 +6,8 @@
  *      Distribute under GPLv2.
  *
  *      Rewritten. Old one was good in 2.2, but in 2.3 it was immoral. --ANK (990903)
+ *
+ *      Remote softirq infrastructure is by Jens Axboe.
  */
 
 #include <linux/module.h>
@@ -474,17 +476,144 @@ void tasklet_kill(struct tasklet_struct *t)
 
 EXPORT_SYMBOL(tasklet_kill);
 
+DEFINE_PER_CPU(struct list_head [NR_SOFTIRQS], softirq_work_list);
+EXPORT_PER_CPU_SYMBOL(softirq_work_list);
+
+static void __local_trigger(struct call_single_data *cp, int softirq)
+{
+        struct list_head *head = &__get_cpu_var(softirq_work_list[softirq]);
+
+        list_add_tail(&cp->list, head);
+
+        /* Trigger the softirq only if the list was previously empty.  */
+        if (head->next == &cp->list)
+                raise_softirq_irqoff(softirq);
+}
+
+#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
+static void remote_softirq_receive(void *data)
+{
+        struct call_single_data *cp = data;
+        unsigned long flags;
+        int softirq;
+
+        softirq = cp->priv;
+
+        local_irq_save(flags);
+        __local_trigger(cp, softirq);
+        local_irq_restore(flags);
+}
+
+static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
+{
+        if (cpu_online(cpu)) {
+                cp->func = remote_softirq_receive;
+                cp->info = cp;
+                cp->flags = 0;
+                cp->priv = softirq;
+
+                __smp_call_function_single(cpu, cp);
+                return 0;
+        }
+        return 1;
+}
+#else /* CONFIG_USE_GENERIC_SMP_HELPERS */
+static int __try_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
+{
+        return 1;
+}
+#endif
+
+/**
+ * __send_remote_softirq - try to schedule softirq work on a remote cpu
+ * @cp: private SMP call function data area
+ * @cpu: the remote cpu
+ * @this_cpu: the currently executing cpu
+ * @softirq: the softirq for the work
+ *
+ * Attempt to schedule softirq work on a remote cpu.  If this cannot be
+ * done, the work is instead queued up on the local cpu.
+ *
+ * Interrupts must be disabled.
+ */
+void __send_remote_softirq(struct call_single_data *cp, int cpu, int this_cpu, int softirq)
+{
+        if (cpu == this_cpu || __try_remote_softirq(cp, cpu, softirq))
+                __local_trigger(cp, softirq);
+}
+EXPORT_SYMBOL(__send_remote_softirq);
+
+/**
+ * send_remote_softirq - try to schedule softirq work on a remote cpu
+ * @cp: private SMP call function data area
+ * @cpu: the remote cpu
+ * @softirq: the softirq for the work
+ *
+ * Like __send_remote_softirq except that disabling interrupts and
+ * computing the current cpu is done for the caller.
+ */
+void send_remote_softirq(struct call_single_data *cp, int cpu, int softirq)
+{
+        unsigned long flags;
+        int this_cpu;
+
+        local_irq_save(flags);
+        this_cpu = smp_processor_id();
+        __send_remote_softirq(cp, cpu, this_cpu, softirq);
+        local_irq_restore(flags);
+}
+EXPORT_SYMBOL(send_remote_softirq);
+
+static int __cpuinit remote_softirq_cpu_notify(struct notifier_block *self,
+                                               unsigned long action, void *hcpu)
+{
+        /*
+         * If a CPU goes away, splice its entries to the current CPU
+         * and trigger a run of the softirq
+         */
+        if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
+                int cpu = (unsigned long) hcpu;
+                int i;
+
+                local_irq_disable();
+                for (i = 0; i < NR_SOFTIRQS; i++) {
+                        struct list_head *head = &per_cpu(softirq_work_list[i], cpu);
+                        struct list_head *local_head;
+
+                        if (list_empty(head))
+                                continue;
+
+                        local_head = &__get_cpu_var(softirq_work_list[i]);
+                        list_splice_init(head, local_head);
+                        raise_softirq_irqoff(i);
+                }
+                local_irq_enable();
+        }
+
+        return NOTIFY_OK;
+}
+
+static struct notifier_block __cpuinitdata remote_softirq_cpu_notifier = {
+        .notifier_call  = remote_softirq_cpu_notify,
+};
+
 void __init softirq_init(void)
 {
         int cpu;
 
         for_each_possible_cpu(cpu) {
+                int i;
+
                 per_cpu(tasklet_vec, cpu).tail =
                         &per_cpu(tasklet_vec, cpu).head;
                 per_cpu(tasklet_hi_vec, cpu).tail =
                         &per_cpu(tasklet_hi_vec, cpu).head;
+                for (i = 0; i < NR_SOFTIRQS; i++)
+                        INIT_LIST_HEAD(&per_cpu(softirq_work_list[i], cpu));
         }
 
+        register_hotcpu_notifier(&remote_softirq_cpu_notifier);
+
         open_softirq(TASKLET_SOFTIRQ, tasklet_action);
         open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 }