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>

1 files changed, 6 insertions, 1 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;
 }