From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754183Ab0BRJJ4 (ORCPT ); Thu, 18 Feb 2010 04:09:56 -0500 Received: from courier.cs.helsinki.fi ([128.214.9.1]:44589 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753280Ab0BRJJx (ORCPT ); Thu, 18 Feb 2010 04:09:53 -0500 Date: Thu, 18 Feb 2010 11:09:51 +0200 (EET) From: "=?ISO-8859-15?Q?Ilpo_J=E4rvinen?=" X-X-Sender: ijjarvin@melkinpaasi.cs.helsinki.fi To: Franco Fichtner cc: Andreas Petlund , Netdev , eric.dumazet@gmail.com, hannemann@nets.rwth-aachen.de, LKML , shemminger@vyatta.com, william.allen.simpson@gmail.com, damian@tvk.rwth-aachen.de, ebiederm@xmission.com, David Miller Subject: Re: [net-next PATCH v4 2/3] net: TCP thin linear timeouts In-Reply-To: <4B7D01CE.1030101@lastsummer.de> Message-ID: References: <4B7AAE69.8020701@simula.no> <20100217.163255.133898079.davem@davemloft.net> <4B7CFDE4.4010003@simula.no> <4B7D01CE.1030101@lastsummer.de> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: MULTIPART/MIXED; BOUNDARY="-696230645-1275017534-1266484191=:9961" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This message is in MIME format. The first part should be readable text, while the remaining parts are likely unreadable without MIME-aware tools. ---696230645-1275017534-1266484191=:9961 Content-Type: TEXT/PLAIN; charset=iso-8859-1 Content-Transfer-Encoding: 8BIT On Thu, 18 Feb 2010, Franco Fichtner wrote: > Andreas Petlund wrote: > > On 02/18/2010 09:41 AM, Ilpo Järvinen wrote: > > > > > On Wed, 17 Feb 2010, David Miller wrote: > > > > > > > > > > From: Andreas Petlund > > > > Date: Tue, 16 Feb 2010 15:40:41 +0100 > > > > > > > > > > > > > @@ -341,6 +342,8 @@ struct tcp_sock { > > > > > u16 advmss; /* Advertised MSS > > > > > */ > > > > > u8 frto_counter; /* Number of new acks after RTO */ > > > > > u8 nonagle; /* Disable Nagle algorithm? > > > > > */ > > > > > + u8 thin_lto : 1,/* Use linear timeouts for thin > > > > > streams */ > > > > > + thin_undef : 7; > > > > > > > > > There is now a gap of 3 unused bytes here in this critical > > > > core TCP socket data structure. > > > > > > > > Please either find a way to avoid this hole, or document > > > > it with a comment. > > > > > > > There would be multiple bits free for use in both frto_counter and nonagle > > > byte. > > > > > > > > > > I was playing aroud with this setup: > > > > ========= > > u8 nonagle : 4,/* Disable Nagle algorithm? */ > > thin_lto : 1,/* Use linear timeouts for thin streams */ > > thin_dupack : 1,/* Fast retransmit on first dupack */ > > thin_undef : 2; > > ========= > > > > Do you think that would do the trick? > > > > According to Ilpo, it would be ok to reduce both ftro_counter and > nonagle, so why not join all these into u16 and leave the remaining > free bits documented for other people. Like this: > > u16 frto_counter:x; /* Number of new acks after RTO */ > u16 nonagle:y; /* Disable Nagle algorithm? */ > u16 thin_lto:1; /* Use linear timeouts for thin streams */ > u16 unused:15-x-y; > > Not sure about the y and x. Ilpo, can you comment on those values? I don't remember top of the hat how much of nonagle used, but for frto_counter max value was 3 iirc. However, I'm unsure if compiler is nowadays wise enough to handle bitfields in some not all so stupid way. Btw, also in ecn_flags we have some empty space. But all in all that didn't vacate enough to get 4 bytes so I haven't taken effort of combining. -- i. ---696230645-1275017534-1266484191=:9961--