kernel: use lockless list for smp_call_function_single

Make smp_call_function_single and friends more efficient by using a
lockless list.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 38 deletions

diff --git a/kernel/smp.c b/kernel/smp.c
index bd9f94028838..4ad913e7c253 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -28,12 +28,7 @@ struct call_function_data {
 
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
 
-struct call_single_queue {
-        struct list_head        list;
-        raw_spinlock_t          lock;
-};
-
-static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_queue, call_single_queue);
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue);
 
 static int
 hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
@@ -85,12 +80,8 @@ void __init call_function_init(void)
         void *cpu = (void *)(long)smp_processor_id();
         int i;
 
-        for_each_possible_cpu(i) {
-                struct call_single_queue *q = &per_cpu(call_single_queue, i);
-
-                raw_spin_lock_init(&q->lock);
-                INIT_LIST_HEAD(&q->list);
-        }
+        for_each_possible_cpu(i)
+                init_llist_head(&per_cpu(call_single_queue, i));
 
         hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
         register_cpu_notifier(&hotplug_cfd_notifier);
@@ -141,18 +132,9 @@ static void csd_unlock(struct call_single_data *csd)
  */
 static void generic_exec_single(int cpu, struct call_single_data *csd, int wait)
 {
-        struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
-        unsigned long flags;
-        int ipi;
-
         if (wait)
                 csd->flags |= CSD_FLAG_WAIT;
 
-        raw_spin_lock_irqsave(&dst->lock, flags);
-        ipi = list_empty(&dst->list);
-        list_add_tail(&csd->list, &dst->list);
-        raw_spin_unlock_irqrestore(&dst->lock, flags);
-
         /*
          * The list addition should be visible before sending the IPI
          * handler locks the list to pull the entry off it because of
@@ -164,7 +146,7 @@ static void generic_exec_single(int cpu, struct call_single_data *csd, int wait)
          * locking and barrier primitives. Generic code isn't really
          * equipped to do the right thing...
          */
-        if (ipi)
+        if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
                 arch_send_call_function_single_ipi(cpu);
 
         if (wait)
@@ -177,27 +159,26 @@ static void generic_exec_single(int cpu, struct call_single_data *csd, int wait)
  */
 void generic_smp_call_function_single_interrupt(void)
 {
-        struct call_single_queue *q = &__get_cpu_var(call_single_queue);
-        LIST_HEAD(list);
+        struct llist_node *entry, *next;
 
         /*
          * Shouldn't receive this interrupt on a cpu that is not yet online.
          */
         WARN_ON_ONCE(!cpu_online(smp_processor_id()));
 
-        raw_spin_lock(&q->lock);
-        list_replace_init(&q->list, &list);
-        raw_spin_unlock(&q->lock);
+        entry = llist_del_all(&__get_cpu_var(call_single_queue));
+        entry = llist_reverse_order(entry);
 
-        while (!list_empty(&list)) {
+        while (entry) {
                 struct call_single_data *csd;
 
-                csd = list_entry(list.next, struct call_single_data, list);
-                list_del(&csd->list);
+                next = entry->next;
 
+                csd = llist_entry(entry, struct call_single_data, llist);
                 csd->func(csd->info);
-
                 csd_unlock(csd);
+
+                entry = next;
         }
 }
 
@@ -411,17 +392,11 @@ void smp_call_function_many(const struct cpumask *mask,
 
         for_each_cpu(cpu, cfd->cpumask) {
                 struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
-                struct call_single_queue *dst =
-                                        &per_cpu(call_single_queue, cpu);
-                unsigned long flags;
 
                 csd_lock(csd);
                 csd->func = func;
                 csd->info = info;
-
-                raw_spin_lock_irqsave(&dst->lock, flags);
-                list_add_tail(&csd->list, &dst->list);
-                raw_spin_unlock_irqrestore(&dst->lock, flags);
+                llist_add(&csd->llist, &per_cpu(call_single_queue, cpu));
         }
 
         /* Send a message to all CPUs in the map */