[PATCH net-next 02/10] tipc: eliminate aggregate sk_receive_queue limit

[Paul Gortmaker <paul.gortmaker@windriver.com>]

From: Ying Xue <ying.xue@windriver.com>

As a complement to the per-socket sk_recv_queue limit, TIPC keeps a
global atomic counter for the sum of sk_recv_queue sizes across all
tipc sockets. When incremented, the counter is compared to an upper
threshold value, and if this is reached, the message is rejected
with error code TIPC_OVERLOAD.

This check was originally meant to protect the node against
buffer exhaustion and general CPU overload. However, all experience
indicates that the feature not only is redundant on Linux, but even
harmful. Users run into the limit very often, causing disturbances
for their applications, while removing it seems to have no negative
effects at all. We have also seen that overall performance is
boosted significantly when this bottleneck is removed.

Furthermore, we don't see any other network protocols maintaining
such a mechanism, something strengthening our conviction that this
control can be eliminated.

Signed-off-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
---
 net/tipc/socket.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index 1a720c8..a059ed0 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -2,7 +2,7 @@
  * net/tipc/socket.c: TIPC socket API
  *
  * Copyright (c) 2001-2007, Ericsson AB
- * Copyright (c) 2004-2008, 2010-2011, Wind River Systems
+ * Copyright (c) 2004-2008, 2010-2012, Wind River Systems
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -1241,11 +1241,6 @@ static u32 filter_rcv(struct sock *sk, struct sk_buff *buf)
 	}
 
 	/* Reject message if there isn't room to queue it */
-	recv_q_len = (u32)atomic_read(&tipc_queue_size);
-	if (unlikely(recv_q_len >= OVERLOAD_LIMIT_BASE)) {
-		if (rx_queue_full(msg, recv_q_len, OVERLOAD_LIMIT_BASE))
-			return TIPC_ERR_OVERLOAD;
-	}
 	recv_q_len = skb_queue_len(&sk->sk_receive_queue);
 	if (unlikely(recv_q_len >= (OVERLOAD_LIMIT_BASE / 2))) {
 		if (rx_queue_full(msg, recv_q_len, OVERLOAD_LIMIT_BASE / 2))
-- 
1.7.12.1