Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754591Ab0BRJSx (ORCPT ); Thu, 18 Feb 2010 04:18:53 -0500 Received: from mail-forward2.uio.no ([129.240.10.71]:59784 "EHLO mail-forward2.uio.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753530Ab0BRJSt (ORCPT ); Thu, 18 Feb 2010 04:18:49 -0500 Message-ID: <4B7D05ED.4060900@simula.no> Date: Thu, 18 Feb 2010 10:18:37 +0100 From: Andreas Petlund User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9pre) Gecko/20100209 Shredder/3.0.2pre MIME-Version: 1.0 To: =?ISO-8859-1?Q?Ilpo_J=E4rvinen?= CC: Franco Fichtner , 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 References: <4B7AAE69.8020701@simula.no> <20100217.163255.133898079.davem@davemloft.net> <4B7CFDE4.4010003@simula.no> <4B7D01CE.1030101@lastsummer.de> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-UiO-Ratelimit-Test: rcpts/h 11 msgs/h 1 sum rcpts/h 17 sum msgs/h 2 total rcpts 879 max rcpts/h 40 ratelimit 0 X-UiO-Spam-info: not spam, SpamAssassin (score=-5.0, required=5.0, autolearn=disabled, UIO_MAIL_IS_INTERNAL=-5, uiobl=NO, uiouri=NO) X-UiO-Scanned: FA37B42F033C1506F435C0F93AD1F5D0AC1A1F64 X-UiO-SPAM-Test: remote_host: 128.39.37.254 spam_score: -49 maxlevel 80 minaction 2 bait 0 mail/h: 13 total 20662 max/h 66 blacklist 0 greylist 0 ratelimit 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2674 Lines: 80 On 02/18/2010 10:09 AM, Ilpo J?rvinen wrote: > On Thu, 18 Feb 2010, Franco Fichtner wrote: > >> Andreas Petlund wrote: >>> On 02/18/2010 09:41 AM, Ilpo J?rvinen 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. I think nonagle uses 4 bits: ====== #define TCP_NAGLE_OFF 1 /* Nagle's algo is disabled */ #define TCP_NAGLE_CORK 2 /* Socket is corked */ #define TCP_NAGLE_PUSH 4 /* Cork is overridden for already queued data */ ====== > However, I'm unsure if compiler is > nowadays wise enough to handle bitfields in some not all so stupid way. Would you then recommend to use a byte for each value, thus avoiding the bitfields? Cheers, Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/