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On Thu, 2010-12-23 at 23:18 +0800, Vivek Goyal wrote:sure, it's harmless anyway and more readable. Updated the patch. 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> --- block/cfq-iosched.c | 23 ++++++++++++----------- 1 file changed, 12 insertions(+), 11 deletions(-) Index: linux/block/cfq-iosched.c =================================================================== --- linux.orig/block/cfq-iosched.c 2010-12-24 08:32:19.000000000 +0800 +++ linux/block/cfq-iosched.c 2010-12-24 08:33:10.000000000 +0800 @@ -209,7 +209,7 @@ 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; @@ -1026,7 +1026,7 @@ cfq_find_alloc_cfqg(struct cfq_data *cfq * 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 @@ -1071,7 +1071,7 @@ static struct cfq_group *cfq_get_cfqg(st static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg) { - atomic_inc(&cfqg->ref); + cfqg->ref++; return cfqg; } @@ -1083,7 +1083,7 @@ static void cfq_link_cfqq_cfqg(struct cf cfqq->cfqg = cfqg; /* cfqq reference on cfqg */ - atomic_inc(&cfqq->cfqg->ref); + cfqq->cfqg->ref++; } static void cfq_put_cfqg(struct cfq_group *cfqg) @@ -1091,8 +1091,9 @@ static void cfq_put_cfqg(struct cfq_grou 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) || st->active != NULL); @@ -1200,7 +1201,7 @@ static void cfq_service_tree_add(struct 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) { @@ -3683,12 +3684,12 @@ 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: @@ -3886,7 +3887,7 @@ static void *cfq_init_queue(struct reque * 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); --