From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Heffner Subject: Re: SWS for rcvbuf < MTU Date: Fri, 02 Mar 2007 16:16:39 -0500 Message-ID: <45E89437.3000902@psc.edu> References: <200703021128.29208.alexandre.sidorenko@hp.com> <20070302.112542.18305896.davem@davemloft.net> <200703021521.58821.alexandre.sidorenko@hp.com> <20070302.123325.28790131.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: alexandre.sidorenko@hp.com, netdev@vger.kernel.org To: David Miller Return-path: Received: from mailer2.psc.edu ([128.182.66.106]:55557 "EHLO mailer2.psc.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965640AbXCBVQr (ORCPT ); Fri, 2 Mar 2007 16:16:47 -0500 In-Reply-To: <20070302.123325.28790131.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org David Miller wrote: > From: Alex Sidorenko > Date: Fri, 2 Mar 2007 15:21:58 -0500 > >> they told us that they use small rcvbuf to throttle bandwidth for this >> application. I explained it would be better to use TC for this purpose. They >> agreed and will probably redesign their application in the future, but they >> cannot do it right now. For the same reason they have to use the old 2.4.20 >> for a while - in big companies the important production software cannot be >> changed quickly. >> >> The fix I suggested is trivial and should have no impact the case of >> rcvfbuf>mtu, so I think it makes sense to include it in upstream kernel. > > I have no objection to the fix, especially John's version. > > I was just curious about the app, thanks for the info :) Please don't apply the patch I sent. I've been thinking about this a bit harder, and it may not fix this particular problem. (Hard to say without knowing exactly what it is.) As the comment above __tcp_select_window() states, we do not do full receive-side SWS avoidance because of header prediction. Alex, you're right I missed that special zero-window case. I'm still not quite sure I'm completely happy with this patch. I'd like to think about this a little bit harder... Thanks, -John