netdev - Re: [PATCH net-next] tcp: TSO packets automatic sizing

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Date:	Sun, 25 Aug 2013 19:22:39 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	Neal Cardwell <ncardwell@...gle.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Van Jacobson <vanj@...gle.com>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: [PATCH net-next] tcp: TSO packets automatic sizing

On Sun, 2013-08-25 at 17:37 -0700, Eric Dumazet wrote:
> On Sun, 2013-08-25 at 15:01 -0700, Yuchung Cheng wrote:
> 
> > Any idea to get rid of this undesirable extra RTT delay?
> 
> Its probably a bug in the push code.

For exact write/send of a multiple of MSS, I think following patch
should fix the bug.

If we filled a packet, we must send it.

For the other problem, I think its related to Nagle.

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index ab64eea..dd326f4 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1187,7 +1187,8 @@ new_segment:
 
 			from += copy;
 			copied += copy;
-			if ((seglen -= copy) == 0 && iovlen == 0)
+			seglen -= copy;
+			if (seglen == 0 && iovlen == 0 && skb->len < max)
 				goto out;
 
 			if (skb->len < max || (flags & MSG_OOB) || unlikely(tp->repair))


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