block/rnbd: Remove all likely and unlikely

The IO performance test with fio after removing the likely and
unlikely macros in all if-statement shows no performance drop.
They do not help for the performance of rnbd.

The fio test did random read on 32 rnbd devices and 64 processes.
Test environment:
- AMD Opteron(tm) Processor 6386 SE
- 125G memory
- kernel version: 5.4.86
- gcc version: gcc (Debian 8.3.0-6) 8.3.0
- Infiniband controller: InfiniBand: Mellanox Technologies MT26428
[ConnectX VPI PCIe 2.0 5GT/s - IB QDR / 10GigE] (rev b0)

before
read: IOPS=549k, BW=2146MiB/s
read: IOPS=544k, BW=2125MiB/s
read: IOPS=553k, BW=2158MiB/s
read: IOPS=535k, BW=2089MiB/s
read: IOPS=543k, BW=2122MiB/s
read: IOPS=552k, BW=2154MiB/s
average: IOPS=546k, BW=2132MiB/s

after
read: IOPS=556k, BW=2172MiB/s
read: IOPS=561k, BW=2191MiB/s
read: IOPS=552k, BW=2156MiB/s
read: IOPS=551k, BW=2154MiB/s
read: IOPS=562k, BW=2194MiB/s
-----------
average: IOPS=556k, BW=2173MiB/s

The IOPS and bandwidth got better slightly after removing
likely/unlikely. (IOPS= +1.8% BW= +1.9%) But we cannot make sure
that removing the likely/unlikely help the performance because it
depends on various situations. We only make sure that removing the
likely/unlikely does not drop the performance.

Signed-off-by: Gioh Kim <[email protected]>
Reviewed-by: Md Haris Iqbal <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Gioh Kim

drivers/block/rnbd/rnbd-clt.c

@@ -241,7 +241,7 @@ static bool rnbd_rerun_if_needed(struct rnbd_clt_session *sess)
 	     cpu_q = rnbd_get_cpu_qlist(sess, nxt_cpu(cpu_q->cpu))) {
 		if (!spin_trylock_irqsave(&cpu_q->requeue_lock, flags))
 			continue;
-		if (unlikely(!test_bit(cpu_q->cpu, sess->cpu_queues_bm)))
+		if (!test_bit(cpu_q->cpu, sess->cpu_queues_bm))
 			goto unlock;
 		q = list_first_entry_or_null(&cpu_q->requeue_list,
 					     typeof(*q), requeue_list);
@@ -320,7 +320,7 @@ static struct rtrs_permit *rnbd_get_permit(struct rnbd_clt_session *sess,
 	struct rtrs_permit *permit;
 
 	permit = rtrs_clt_get_permit(sess->rtrs, con_type, wait);
-	if (likely(permit))
+	if (permit)
 		/* We have a subtle rare case here, when all permits can be
 		 * consumed before busy counter increased.  This is safe,
 		 * because loser will get NULL as a permit, observe 0 busy
@@ -355,7 +355,7 @@ static struct rnbd_iu *rnbd_get_iu(struct rnbd_clt_session *sess,
 		return NULL;
 
 	permit = rnbd_get_permit(sess, con_type, wait);
-	if (unlikely(!permit)) {
+	if (!permit) {
 		kfree(iu);
 		return NULL;
 	}
@@ -1050,7 +1050,7 @@ static int rnbd_client_xfer_request(struct rnbd_clt_dev *dev,
 	};
 	err = rtrs_clt_request(rq_data_dir(rq), &req_ops, rtrs, permit,
 			       &vec, 1, size, iu->sgt.sgl, sg_cnt);
-	if (unlikely(err)) {
+	if (err) {
 		rnbd_clt_err_rl(dev, "RTRS failed to transfer IO, err: %d\n",
 				 err);
 		return err;
@@ -1081,7 +1081,7 @@ static bool rnbd_clt_dev_add_to_requeue(struct rnbd_clt_dev *dev,
 	cpu_q = get_cpu_ptr(sess->cpu_queues);
 	spin_lock_irqsave(&cpu_q->requeue_lock, flags);
 
-	if (likely(!test_and_set_bit_lock(0, &q->in_list))) {
+	if (!test_and_set_bit_lock(0, &q->in_list)) {
 		if (WARN_ON(!list_empty(&q->requeue_list)))
 			goto unlock;
 
@@ -1093,7 +1093,7 @@ static bool rnbd_clt_dev_add_to_requeue(struct rnbd_clt_dev *dev,
 			 */
 			smp_mb__before_atomic();
 		}
-		if (likely(atomic_read(&sess->busy))) {
+		if (atomic_read(&sess->busy)) {
 			list_add_tail(&q->requeue_list, &cpu_q->requeue_list);
 		} else {
 			/* Very unlikely, but possible: busy counter was
@@ -1121,7 +1121,7 @@ static void rnbd_clt_dev_kick_mq_queue(struct rnbd_clt_dev *dev,
 
 	if (delay != RNBD_DELAY_IFBUSY)
 		blk_mq_delay_run_hw_queue(hctx, delay);
-	else if (unlikely(!rnbd_clt_dev_add_to_requeue(dev, q)))
+	else if (!rnbd_clt_dev_add_to_requeue(dev, q))
 		/*
 		 * If session is not busy we have to restart
 		 * the queue ourselves.
@@ -1138,12 +1138,12 @@ static blk_status_t rnbd_queue_rq(struct blk_mq_hw_ctx *hctx,
 	int err;
 	blk_status_t ret = BLK_STS_IOERR;
 
-	if (unlikely(dev->dev_state != DEV_STATE_MAPPED))
+	if (dev->dev_state != DEV_STATE_MAPPED)
 		return BLK_STS_IOERR;
 
 	iu->permit = rnbd_get_permit(dev->sess, RTRS_IO_CON,
 				      RTRS_PERMIT_NOWAIT);
-	if (unlikely(!iu->permit)) {
+	if (!iu->permit) {
 		rnbd_clt_dev_kick_mq_queue(dev, hctx, RNBD_DELAY_IFBUSY);
 		return BLK_STS_RESOURCE;
 	}
@@ -1165,9 +1165,9 @@ static blk_status_t rnbd_queue_rq(struct blk_mq_hw_ctx *hctx,
 
 	blk_mq_start_request(rq);
 	err = rnbd_client_xfer_request(dev, rq, iu);
-	if (likely(err == 0))
+	if (err == 0)
 		return BLK_STS_OK;
-	if (unlikely(err == -EAGAIN || err == -ENOMEM)) {
+	if (err == -EAGAIN || err == -ENOMEM) {
 		rnbd_clt_dev_kick_mq_queue(dev, hctx, 10/*ms*/);
 		ret = BLK_STS_RESOURCE;
 	}
@@ -1584,7 +1584,7 @@ struct rnbd_clt_dev *rnbd_clt_map_device(const char *sessname,
 	struct rnbd_clt_dev *dev;
 	int ret;
 
-	if (unlikely(exists_devpath(pathname, sessname)))
+	if (exists_devpath(pathname, sessname))
 		return ERR_PTR(-EEXIST);
 
 	sess = find_and_get_or_create_sess(sessname, paths, path_cnt, port_nr, nr_poll_queues);

drivers/block/rnbd/rnbd-srv.c

@@ -104,7 +104,7 @@ rnbd_get_sess_dev(int dev_id, struct rnbd_srv_session *srv_sess)
 
 	rcu_read_lock();
 	sess_dev = xa_load(&srv_sess->index_idr, dev_id);
-	if (likely(sess_dev))
+	if (sess_dev)
 		ret = kref_get_unless_zero(&sess_dev->kref);
 	rcu_read_unlock();