[PATCH] RPC: separate xprt_timer implementations

 Allow transports to hook the retransmit timer interrupt.  Some transports
 calculate their congestion window here so that a retransmit timeout has
 immediate effect on the congestion window.

 Test-plan:
 Use WAN simulation to cause sporadic bursty packet loss.  Look for significant
 regression in performance or client stability.

 Signed-off-by: Chuck Lever <cel@netapp.com>
 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

3 files changed, 34 insertions, 25 deletions

diff --git a/include/linux/sunrpc/xprt.h b/include/linux/sunrpc/xprt.h
index 86833b725bb5..443c3f984cf9 100644
--- a/include/linux/sunrpc/xprt.h
+++ b/include/linux/sunrpc/xprt.h
@@ -137,6 +137,7 @@ struct rpc_xprt_ops {
         void            (*connect)(struct rpc_task *task);
         int             (*send_request)(struct rpc_task *task);
         void            (*set_retrans_timeout)(struct rpc_task *task);
+        void            (*timer)(struct rpc_task *task);
         void            (*close)(struct rpc_xprt *xprt);
         void            (*destroy)(struct rpc_xprt *xprt);
 };
@@ -257,6 +258,7 @@ void			xprt_set_retrans_timeout_rtt(struct rpc_task *task);
 void                    xprt_wake_pending_tasks(struct rpc_xprt *xprt, int status);
 void                    xprt_wait_for_buffer_space(struct rpc_task *task);
 void                    xprt_write_space(struct rpc_xprt *xprt);
+void                    xprt_adjust_cwnd(struct rpc_task *task, int result);
 struct rpc_rqst *       xprt_lookup_rqst(struct rpc_xprt *xprt, u32 xid);
 void                    xprt_complete_rqst(struct rpc_xprt *xprt, struct rpc_rqst *req, int copied);
 void                    xprt_disconnect(struct rpc_xprt *xprt);
diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index e92ea99dd318..ffc595592af3 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -289,16 +289,19 @@ __xprt_put_cong(struct rpc_xprt *xprt, struct rpc_rqst *req)
         __xprt_lock_write_next_cong(xprt);
 }
 
-/*
- * Adjust RPC congestion window
+/**
+ * xprt_adjust_cwnd - adjust transport congestion window
+ * @task: recently completed RPC request used to adjust window
+ * @result: result code of completed RPC request
+ *
  * We use a time-smoothed congestion estimator to avoid heavy oscillation.
  */
-static void
-xprt_adjust_cwnd(struct rpc_xprt *xprt, int result)
+void xprt_adjust_cwnd(struct rpc_task *task, int result)
 {
-        unsigned long   cwnd;
+        struct rpc_rqst *req = task->tk_rqstp;
+        struct rpc_xprt *xprt = task->tk_xprt;
+        unsigned long cwnd = xprt->cwnd;
 
-        cwnd = xprt->cwnd;
         if (result >= 0 && cwnd <= xprt->cong) {
                 /* The (cwnd >> 1) term makes sure
                  * the result gets rounded properly. */
@@ -314,6 +317,7 @@ xprt_adjust_cwnd(struct rpc_xprt *xprt, int result)
         dprintk("RPC:      cong %ld, cwnd was %ld, now %ld\n",
                         xprt->cong, xprt->cwnd, cwnd);
         xprt->cwnd = cwnd;
+        __xprt_put_cong(xprt, req);
 }
 
 /**
@@ -602,8 +606,7 @@ void xprt_complete_rqst(struct rpc_xprt *xprt, struct rpc_rqst *req, int copied)
         /* Adjust congestion window */
         if (!xprt->nocong) {
                 unsigned timer = task->tk_msg.rpc_proc->p_timer;
-                xprt_adjust_cwnd(xprt, copied);
-                __xprt_put_cong(xprt, req);
+                xprt_adjust_cwnd(task, copied);
                 if (timer) {
                         if (req->rq_ntrans == 1)
                                 rpc_update_rtt(clnt->cl_rtt, timer,
@@ -640,27 +643,19 @@ void xprt_complete_rqst(struct rpc_xprt *xprt, struct rpc_rqst *req, int copied)
         return;
 }
 
-/*
- * RPC receive timeout handler.
- */
-static void
-xprt_timer(struct rpc_task *task)
+static void xprt_timer(struct rpc_task *task)
 {
-        struct rpc_rqst *req = task->tk_rqstp;
+        struct rpc_rqst *req = task->tk_rqstp;
         struct rpc_xprt *xprt = req->rq_xprt;
 
-        spin_lock(&xprt->transport_lock);
-        if (req->rq_received)
-                goto out;
-
-        xprt_adjust_cwnd(req->rq_xprt, -ETIMEDOUT);
-        __xprt_put_cong(xprt, req);
+        dprintk("RPC: %4d xprt_timer\n", task->tk_pid);
 
-        dprintk("RPC: %4d xprt_timer (%s request)\n",
-                task->tk_pid, req ? "pending" : "backlogged");
-
-        task->tk_status  = -ETIMEDOUT;
-out:
+        spin_lock(&xprt->transport_lock);
+        if (!req->rq_received) {
+                if (xprt->ops->timer)
+                        xprt->ops->timer(task);
+                task->tk_status = -ETIMEDOUT;
+        }
         task->tk_timeout = 0;
         rpc_wake_up_task(task);
         spin_unlock(&xprt->transport_lock);
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
index 8589c1ad55e3..c3658ff027a6 100644
--- a/net/sunrpc/xprtsock.c
+++ b/net/sunrpc/xprtsock.c
@@ -860,6 +860,17 @@ static void xs_tcp_set_buffer_size(struct rpc_xprt *xprt)
         return;
 }
 
+/**
+ * xs_udp_timer - called when a retransmit timeout occurs on a UDP transport
+ * @task: task that timed out
+ *
+ * Adjust the congestion window after a retransmit timeout has occurred.
+ */
+static void xs_udp_timer(struct rpc_task *task)
+{
+        xprt_adjust_cwnd(task, -ETIMEDOUT);
+}
+
 static int xs_bindresvport(struct rpc_xprt *xprt, struct socket *sock)
 {
         struct sockaddr_in myaddr = {
@@ -1050,6 +1061,7 @@ static struct rpc_xprt_ops xs_udp_ops = {
         .connect                = xs_connect,
         .send_request           = xs_udp_send_request,
         .set_retrans_timeout    = xprt_set_retrans_timeout_rtt,
+        .timer                  = xs_udp_timer,
         .close                  = xs_close,
         .destroy                = xs_destroy,
 };