Btrfs: reduce worker thread spin_lock_irq hold times

This changes the btrfs worker threads to batch work items
into a local list.  It allows us to pull work items in
large chunks and significantly reduces the number of times we
need to take the worker thread spinlock.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c
index 4b4372df3b6d3b14e813cf1db8b530c94080482a..6ea5cd0a595fd165b6d24c38e644e195fe69930f 100644 (file)
--- a/fs/btrfs/async-thread.c
+++ b/fs/btrfs/async-thread.c
@@ -196,31 +196,73 @@ static int try_worker_shutdown(struct btrfs_worker_thread *worker)
        return freeit;
 }
 
+static struct btrfs_work *get_next_work(struct btrfs_worker_thread *worker,
+                                       struct list_head *prio_head,
+                                       struct list_head *head)
+{
+       struct btrfs_work *work = NULL;
+       struct list_head *cur = NULL;
+
+       if(!list_empty(prio_head))
+               cur = prio_head->next;
+
+       smp_mb();
+       if (!list_empty(&worker->prio_pending))
+               goto refill;
+
+       if (!list_empty(head))
+               cur = head->next;
+
+       if (cur)
+               goto out;
+
+refill:
+       spin_lock_irq(&worker->lock);
+       list_splice_tail_init(&worker->prio_pending, prio_head);
+       list_splice_tail_init(&worker->pending, head);
+
+       if (!list_empty(prio_head))
+               cur = prio_head->next;
+       else if (!list_empty(head))
+               cur = head->next;
+       spin_unlock_irq(&worker->lock);
+
+       if (!cur)
+               goto out_fail;
+
+out:
+       work = list_entry(cur, struct btrfs_work, list);
+
+out_fail:
+       return work;
+}
+
 /*
  * main loop for servicing work items
  */
 static int worker_loop(void *arg)
 {
        struct btrfs_worker_thread *worker = arg;
-       struct list_head *cur;
+       struct list_head head;
+       struct list_head prio_head;
        struct btrfs_work *work;
+
+       INIT_LIST_HEAD(&head);
+       INIT_LIST_HEAD(&prio_head);
+
        do {
-               spin_lock_irq(&worker->lock);
-again_locked:
+again:
                while (1) {
-                       if (!list_empty(&worker->prio_pending))
-                               cur = worker->prio_pending.next;
-                       else if (!list_empty(&worker->pending))
-                               cur = worker->pending.next;
-                       else
+
+
+                       work = get_next_work(worker, &prio_head, &head);
+                       if (!work)
                                break;
 
-                       work = list_entry(cur, struct btrfs_work, list);
                        list_del(&work->list);
                        clear_bit(WORK_QUEUED_BIT, &work->flags);
 
                        work->worker = worker;
-                       spin_unlock_irq(&worker->lock);
 
                        work->func(work);
 
@@ -233,9 +275,11 @@ again_locked:
 
                        check_pending_worker_creates(worker);
 
-                       spin_lock_irq(&worker->lock);
-                       check_idle_worker(worker);
                }
+
+               spin_lock_irq(&worker->lock);
+               check_idle_worker(worker);
+
                if (freezing(current)) {
                        worker->working = 0;
                        spin_unlock_irq(&worker->lock);
@@ -274,8 +318,10 @@ again_locked:
                                spin_lock_irq(&worker->lock);
                                set_current_state(TASK_INTERRUPTIBLE);
                                if (!list_empty(&worker->pending) ||
-                                   !list_empty(&worker->prio_pending))
-                                       goto again_locked;
+                                   !list_empty(&worker->prio_pending)) {
+                                       spin_unlock_irq(&worker->lock);
+                                       goto again;
+                               }
 
                                /*
                                 * this makes sure we get a wakeup when someone