SUNRPC: Replace dprintk() call site in xprt_prepare_transmit

Generate a trace event when an RPC request is queued without being
sent immediately.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/trace/events/sunrpc.h

@@ -1093,6 +1093,7 @@ DECLARE_EVENT_CLASS(xprt_writelock_event,
 
 DEFINE_WRITELOCK_EVENT(reserve_xprt);
 DEFINE_WRITELOCK_EVENT(release_xprt);
+DEFINE_WRITELOCK_EVENT(transmit_queued);
 
 DECLARE_EVENT_CLASS(xprt_cong_event,
 	TP_PROTO(

net/sunrpc/xprt.c

@@ -1408,9 +1408,9 @@ bool xprt_prepare_transmit(struct rpc_task *task)
 	struct rpc_rqst	*req = task->tk_rqstp;
 	struct rpc_xprt	*xprt = req->rq_xprt;
 
-	dprintk("RPC: %5u xprt_prepare_transmit\n", task->tk_pid);
-
 	if (!xprt_lock_write(xprt, task)) {
+		trace_xprt_transmit_queued(xprt, task);
+
 		/* Race breaker: someone may have transmitted us */
 		if (!test_bit(RPC_TASK_NEED_XMIT, &task->tk_runstate))
 			rpc_wake_up_queued_task_set_status(&xprt->sending,