On Wed, Jun 30, 2010 at 2:03 PM, Ben Hutchings
[off-list ref] wrote:

On Wed, 2010-06-30 at 11:04 -0700, Ivan Novick wrote:

quoted

Hello all,

Attached is a packet capture from my application that is running on
RedHat Enterprise Linux 5.4

I am seeing a Retransmission timeout but I was hoping this case would
go into fast retransmit and not RTO.

I am wondering why did the sender not send more data?  If the sender
was to send more data and extend the window then it would seem the
duplicate acks or SACKS should trigger fast retransmit.

[...]

In that packet capture I see TCP payload lengths which are 2, 3 and 4
times the usual MSS of 1448 bytes, which implies that GRO or LRO is in
use.  In RHEL 5.4 the TCP stack does not ACK often enough in this case
because it is missing this change:

commit ff9b5e0f08cb650d113eef0c654f931c0a7ae730
Author: Herbert Xu [off-list ref]
Date:   Thu Aug 31 15:11:02 2006 -0700

   [TCP]: Fix rcv mss estimate for LRO

Wow, Thanks! Is this the patch you are talking about:
http://www.mail-archive.com/netdev@vger.kernel.org/msg21151.html  ?

It looks like a one liner.   I could apply it and rebuild my RHEL 5.4
to see if it helps.

Cheers,
Ivan Novick