block cfq: don't use atomic_t for cfq_group
Shaohua Li [Fri, 7 Jan 2011 07:48:28 +0000 (08:48 +0100)]
cfq_group->ref is used with queue_lock hold, the only exception is
cfq_set_request, which looks like a bug to me, so ref doesn't need
to be an atomic and atomic operation is slower.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

block/cfq-iosched.c

index 4cb4cf7..f083bda 100644 (file)
@@ -207,7 +207,7 @@ struct cfq_group {
        struct blkio_group blkg;
 #ifdef CONFIG_CFQ_GROUP_IOSCHED
        struct hlist_node cfqd_node;
-       atomic_t ref;
+       int ref;
 #endif
        /* number of requests that are on the dispatch list or inside driver */
        int dispatched;
@@ -1014,7 +1014,7 @@ cfq_find_alloc_cfqg(struct cfq_data *cfqd, struct cgroup *cgroup, int create)
         * elevator which will be dropped by either elevator exit
         * or cgroup deletion path depending on who is exiting first.
         */
-       atomic_set(&cfqg->ref, 1);
+       cfqg->ref = 1;
 
        /*
         * Add group onto cgroup list. It might happen that bdi->dev is
@@ -1059,7 +1059,7 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
 
 static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg)
 {
-       atomic_inc(&cfqg->ref);
+       cfqg->ref++;
        return cfqg;
 }
 
@@ -1071,7 +1071,7 @@ static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
 
        cfqq->cfqg = cfqg;
        /* cfqq reference on cfqg */
-       atomic_inc(&cfqq->cfqg->ref);
+       cfqq->cfqg->ref++;
 }
 
 static void cfq_put_cfqg(struct cfq_group *cfqg)
@@ -1079,8 +1079,9 @@ static void cfq_put_cfqg(struct cfq_group *cfqg)
        struct cfq_rb_root *st;
        int i, j;
 
-       BUG_ON(atomic_read(&cfqg->ref) <= 0);
-       if (!atomic_dec_and_test(&cfqg->ref))
+       BUG_ON(cfqg->ref <= 0);
+       cfqg->ref--;
+       if (cfqg->ref)
                return;
        for_each_cfqg_st(cfqg, i, j, st)
                BUG_ON(!RB_EMPTY_ROOT(&st->rb));
@@ -1188,7 +1189,7 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                        cfq_group_service_tree_del(cfqd, cfqq->cfqg);
                cfqq->orig_cfqg = cfqq->cfqg;
                cfqq->cfqg = &cfqd->root_group;
-               atomic_inc(&cfqd->root_group.ref);
+               cfqd->root_group.ref++;
                group_changed = 1;
        } else if (!cfqd->cfq_group_isolation
                   && cfqq_type(cfqq) == SYNC_WORKLOAD && cfqq->orig_cfqg) {
@@ -3681,12 +3682,12 @@ new_queue:
 
        cfqq->allocated[rw]++;
        cfqq->ref++;
-
-       spin_unlock_irqrestore(q->queue_lock, flags);
-
        rq->elevator_private = cic;
        rq->elevator_private2 = cfqq;
        rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg);
+
+       spin_unlock_irqrestore(q->queue_lock, flags);
+
        return 0;
 
 queue_fail:
@@ -3884,7 +3885,7 @@ static void *cfq_init_queue(struct request_queue *q)
         * Take a reference to root group which we never drop. This is just
         * to make sure that cfq_put_cfqg() does not try to kfree root group
         */
-       atomic_set(&cfqg->ref, 1);
+       cfqg->ref = 1;
        rcu_read_lock();
        cfq_blkiocg_add_blkio_group(&blkio_root_cgroup, &cfqg->blkg,
                                        (void *)cfqd, 0);