[PATCH] RPC over UDP congestion control updates [8/8]

When determining who gets access to the socket, give priority to
requests that are being resent. Despite the fact that congestion
control now applies to resends, we still want to ensure that resends
get ACKed as soon as possible (and before we start sending off new
requests).

include/linux/sunrpc/xprt.h

@@ -123,6 +123,7 @@ struct rpc_xprt {
 	unsigned long		cwnd;		/* congestion window */
 
 	struct rpc_wait_queue	sending;	/* requests waiting to send */
+	struct rpc_wait_queue	resend;		/* requests waiting to resend */
 	struct rpc_wait_queue	pending;	/* requests in flight */
 	struct rpc_wait_queue	backlog;	/* waiting for slot */
 	struct rpc_rqst *	free;		/* free slots */

net/sunrpc/xprt.c

@@ -150,7 +150,10 @@ xprt_lock_write(struct rpc_xprt *xprt, struct rpc_task *task)
 			task->tk_pid, xprt->snd_task->tk_pid);
 		task->tk_timeout = 0;
 		task->tk_status = -EAGAIN;
-		rpc_sleep_on(&xprt->sending, task, NULL, NULL);
+		if (task->tk_rqstp->rq_nresend)
+			rpc_sleep_on(&xprt->resend, task, NULL, NULL);
+		else
+			rpc_sleep_on(&xprt->sending, task, NULL, NULL);
 	}
 	retval = xprt->snd_task == task;
 	spin_unlock_bh(&xprt->sock_lock);
@@ -166,9 +169,12 @@ __xprt_lock_write_next(struct rpc_xprt *xprt)
 		return;
 	if (!xprt->nocong && RPCXPRT_CONGESTED(xprt))
 		return;
-	task = rpc_wake_up_next(&xprt->sending);
-	if (!task)
-		return;
+	task = rpc_wake_up_next(&xprt->resend);
+	if (!task) {
+		task = rpc_wake_up_next(&xprt->sending);
+		if (!task)
+			return;
+	}
 	if (xprt->nocong || __xprt_get_cong(xprt, task))
 		xprt->snd_task = task;
 }
@@ -1346,6 +1352,7 @@ xprt_setup(struct socket *sock, int proto,
 
 	INIT_RPC_WAITQ(&xprt->pending, "xprt_pending");
 	INIT_RPC_WAITQ(&xprt->sending, "xprt_sending");
+	INIT_RPC_WAITQ(&xprt->resend, "xprt_resend");
 	INIT_RPC_WAITQ(&xprt->backlog, "xprt_backlog");
 
 	/* initialize free list */
@@ -1477,6 +1484,7 @@ xprt_shutdown(struct rpc_xprt *xprt)
 {
 	xprt->shutdown = 1;
 	rpc_wake_up(&xprt->sending);
+	rpc_wake_up(&xprt->resend);
 	rpc_wake_up(&xprt->pending);
 	rpc_wake_up(&xprt->backlog);
 	if (waitqueue_active(&xprt->cong_wait))