[PATCH 6/8] nvme-tcp: reduce callback lock contention

[Hannes Reinecke]

From: Hannes Reinecke <hare at suse.de>

We have heavily queued tx and rx flows, so callbacks might happen
at the same time. As the callbacks influence the state machine we
really should remove contention here to not impact I/O performance.

Signed-off-by: Hannes Reinecke <hare at kernel.org>
---
 drivers/nvme/host/tcp.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index a758fbb3f9bb..9634c16d7bc0 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -1153,28 +1153,28 @@ static void nvme_tcp_data_ready(struct sock *sk)
 
 	trace_sk_data_ready(sk);
 
-	read_lock_bh(&sk->sk_callback_lock);
-	queue = sk->sk_user_data;
+	rcu_read_lock();
+	queue = rcu_dereference_sk_user_data(sk);
 	if (likely(queue && queue->rd_enabled) &&
 	    !test_bit(NVME_TCP_Q_POLLING, &queue->flags)) {
 		queue_work_on(queue->io_cpu, nvme_tcp_wq, &queue->io_work);
 		queue->data_ready_cnt++;
 	}
-	read_unlock_bh(&sk->sk_callback_lock);
+	rcu_read_unlock();
 }
 
 static void nvme_tcp_write_space(struct sock *sk)
 {
 	struct nvme_tcp_queue *queue;
 
-	read_lock_bh(&sk->sk_callback_lock);
-	queue = sk->sk_user_data;
+	rcu_read_lock();
+	queue = rcu_dereference_sk_user_data(sk);
 	if (likely(queue && sk_stream_is_writeable(sk))) {
 		clear_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 		queue_work_on(queue->io_cpu, nvme_tcp_wq, &queue->io_work);
 		queue->write_space_cnt++;
 	}
-	read_unlock_bh(&sk->sk_callback_lock);
+	rcu_read_unlock();
 }
 
 static void nvme_tcp_state_change(struct sock *sk)
@@ -2076,6 +2076,7 @@ static void nvme_tcp_restore_sock_ops(struct nvme_tcp_queue *queue)
 	sock->sk->sk_state_change = queue->state_change;
 	sock->sk->sk_write_space  = queue->write_space;
 	write_unlock_bh(&sock->sk->sk_callback_lock);
+	synchronize_rcu();
 }
 
 static void __nvme_tcp_stop_queue(struct nvme_tcp_queue *queue)
@@ -2115,6 +2116,7 @@ static void nvme_tcp_setup_sock_ops(struct nvme_tcp_queue *queue)
 	queue->sock->sk->sk_ll_usec = 1;
 #endif
 	write_unlock_bh(&queue->sock->sk->sk_callback_lock);
+	synchronize_rcu();
 }
 
 static int nvme_tcp_start_queue(struct nvme_ctrl *nctrl, int idx)
-- 
2.35.3