[PATCH] as-iosched: use new io context counting mechanism

It's ok if the read path is a lot more costly, as long as inc/dec is
really cheap. The inc/dec will happen for each created/freed io context,
while the reading only happens when a disk queue exits.
Signed-off-by: Jens Axboe <axboe@suse.de>

block/as-iosched.c

@@ -149,7 +149,7 @@ enum arq_state {
 #define RQ_STATE(rq)	((enum arq_state)(rq)->elevator_private2)
 #define RQ_SET_STATE(rq, state)	((rq)->elevator_private2 = (void *) state)
 
-static atomic_t ioc_count = ATOMIC_INIT(0);
+static DEFINE_PER_CPU(unsigned long, ioc_count);
 static struct completion *ioc_gone;
 
 static void as_move_to_dispatch(struct as_data *ad, struct request *rq);
@@ -163,7 +163,8 @@ static void as_antic_stop(struct as_data *ad);
 static void free_as_io_context(struct as_io_context *aic)
 {
 	kfree(aic);
-	if (atomic_dec_and_test(&ioc_count) && ioc_gone)
+	elv_ioc_count_dec(ioc_count);
+	if (ioc_gone && !elv_ioc_count_read(ioc_count))
 		complete(ioc_gone);
 }
 
@@ -199,7 +200,7 @@ static struct as_io_context *alloc_as_io_context(void)
 		ret->seek_total = 0;
 		ret->seek_samples = 0;
 		ret->seek_mean = 0;
-		atomic_inc(&ioc_count);
+		elv_ioc_count_inc(ioc_count);
 	}
 
 	return ret;
@@ -1484,7 +1485,7 @@ static void __exit as_exit(void)
 	ioc_gone = &all_gone;
 	/* ioc_gone's update must be visible before reading ioc_count */
 	smp_wmb();
-	if (atomic_read(&ioc_count))
+	if (elv_ioc_count_read(ioc_count))
 		wait_for_completion(ioc_gone);
 	synchronize_rcu();
 }