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>

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 0375654..8678c43 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -95,10 +95,7 @@ enum rq_cmd_type_bits {
  * as well!
  */
 struct request {
-       union {
-               struct list_head queuelist;
-               struct llist_node ll_list;
-       };
+       struct list_head queuelist;
        union {
                struct call_single_data csd;
                struct work_struct mq_flush_data;

diff --git a/include/linux/smp.h b/include/linux/smp.h
index 5da22ee..3834f43 100644 (file)
--- a/include/linux/smp.h
+++ b/include/linux/smp.h
@@ -11,12 +11,16 @@
 #include <linux/list.h>
 #include <linux/cpumask.h>
 #include <linux/init.h>
+#include <linux/llist.h>
 
 extern void cpu_idle(void);
 
 typedef void (*smp_call_func_t)(void *info);
 struct call_single_data {
-       struct list_head list;
+       union {
+               struct list_head list;
+               struct llist_node llist;
+       };
        smp_call_func_t func;
        void *info;
        u16 flags;

diff --git a/kernel/smp.c b/kernel/smp.c
index bd9f940..4ad913e 100644 (file)
--- 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 */