netdev - [PATCH V2 net-next] tcp: increase size at which tcp_bound_to_half_wnd bounds to > TCP_MSS

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Message-ID: <CS1PR84MB0295BC70B8ACF200C11B5E25FD220@CS1PR84MB0295.NAMPRD84.PROD.OUTLOOK.COM>
Date:	Tue, 28 Jun 2016 23:06:48 +0000
From:	"Seymour, Shane M" <shane.seymour@....com>
To:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	Eric Dumazet <eric.dumazet@...il.com>
Subject: [PATCH V2 net-next] tcp: increase size at which tcp_bound_to_half_wnd
 bounds to > TCP_MSS_DEFAULT

In previous commit 01f83d69844d307be2aa6fea88b0e8fe5cbdb2f4
the following comments were added:

"When peer uses tiny windows, there is no use in packetizing to sub-MSS
pieces for the sake of SWS or making sure there are enough packets in
the pipe for fast recovery."

The test should be > TCP_MSS_DEFAULT not >= 512. This allows low end
devices that send an MSS of 536 (TCP_MSS_DEFAULT) to see better network
performance by sending it 536 bytes of data at a time instead of bounding
to half window size (268). Other network stacks work this way, e.g. HP-UX.

Signed-off-by: Shane Seymour <shane.seymour@....com>
---
Changed from V1 - patch reversed, Doh!, corrected patch.
--- a/include/net/tcp.h	2016-06-15 17:19:21.964821477 -0500
+++ b/include/net/tcp.h	2016-06-23 20:59:14.521686048 -0500
@@ -589,7 +589,7 @@ static inline int tcp_bound_to_half_wnd(
 	 * On the other hand, for extremely large MSS devices, handling
 	 * smaller than MSS windows in this way does make sense.
 	 */
-	if (tp->max_window >= 512)
+	if (tp->max_window > TCP_MSS_DEFAULT)
 		cutoff = (tp->max_window >> 1);
 	else
 		cutoff = tp->max_window;