RDS: only put sockets that have seen congestion on the poll_waitq

rds_poll_waitq's listeners will be awoken if we receive a congestion
notification. Bad performance may result because *all* polled sockets
contend for this single lock. However, it should not be necessary to
wake pollers when a congestion update arrives if they have never
experienced congestion, and not putting these on the waitq will
hopefully greatly reduce contention.

Signed-off-by: Andy Grover <andy.grover@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 11 insertions, 2 deletions

diff --git a/net/rds/af_rds.c b/net/rds/af_rds.c
index 853c52be781f..937ecda4abe7 100644
--- a/net/rds/af_rds.c
+++ b/net/rds/af_rds.c
@@ -159,7 +159,8 @@ static unsigned int rds_poll(struct file *file, struct socket *sock,
 
         poll_wait(file, sk->sk_sleep, wait);
 
-        poll_wait(file, &rds_poll_waitq, wait);
+        if (rs->rs_seen_congestion)
+                poll_wait(file, &rds_poll_waitq, wait);
 
         read_lock_irqsave(&rs->rs_recv_lock, flags);
         if (!rs->rs_cong_monitor) {
@@ -181,6 +182,10 @@ static unsigned int rds_poll(struct file *file, struct socket *sock,
                 mask |= (POLLOUT | POLLWRNORM);
         read_unlock_irqrestore(&rs->rs_recv_lock, flags);
 
+        /* clear state any time we wake a seen-congested socket */
+        if (mask)
+                rs->rs_seen_congestion = 0;
+
         return mask;
 }
 
diff --git a/net/rds/rds.h b/net/rds/rds.h
index 85d6f897ecc7..4bec6e2ed495 100644
--- a/net/rds/rds.h
+++ b/net/rds/rds.h
@@ -388,6 +388,8 @@ struct rds_sock {
 
         /* flag indicating we were congested or not */
         int                     rs_congested;
+        /* seen congestion (ENOBUFS) when sending? */
+        int                     rs_seen_congestion;
 
         /* rs_lock protects all these adjacent members before the newline */
         spinlock_t              rs_lock;
diff --git a/net/rds/send.c b/net/rds/send.c
index 192a480076d0..51e2def50b12 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -894,8 +894,10 @@ int rds_sendmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
                 queue_delayed_work(rds_wq, &conn->c_conn_w, 0);
 
         ret = rds_cong_wait(conn->c_fcong, dport, nonblock, rs);
-        if (ret)
+        if (ret) {
+                rs->rs_seen_congestion = 1;
                 goto out;
+        }
 
         while (!rds_send_queue_rm(rs, conn, rm, rs->rs_bound_port,
                                   dport, &queued)) {