Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932279Ab0GODtW (ORCPT ); Wed, 14 Jul 2010 23:49:22 -0400 Received: from elasmtp-kukur.atl.sa.earthlink.net ([209.86.89.65]:36383 "EHLO elasmtp-kukur.atl.sa.earthlink.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932260Ab0GODtV (ORCPT ); Wed, 14 Jul 2010 23:49:21 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=mindspring.com; b=ESxIuLgMu0l1cWxma2lplBsz0Tdnt8cXpMwjg39L9+aYz9CmU7S+NH9tIIKmzUN+; h=Received:Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References:X-Mailer:Mime-Version:Content-Type:Content-Transfer-Encoding:X-ELNK-Trace:X-Originating-IP; Date: Wed, 14 Jul 2010 23:49:17 -0400 From: Bill Fink To: Hagen Paul Pfeifer Cc: David Miller , rick.jones2@hp.com, lists@wildgooses.com, davidsen@tmr.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: Raise initial congestion window size / speedup slow start? Message-Id: <20100714234917.924f420d.billfink@mindspring.com> In-Reply-To: <20100714221301.GI6682@nuttenaction> References: <4C3E0684.5060409@wildgooses.com> <4C3E1B54.40604@hp.com> <20100714203919.GD6682@nuttenaction> <20100714.145547.102555471.davem@davemloft.net> <20100714221301.GI6682@nuttenaction> X-Mailer: Sylpheed 2.6.0 (GTK+ 2.16.6; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-ELNK-Trace: c598f748b88b6fd49c7f779228e2f6aeda0071232e20db4d813b51c1c624ff355949692513d24cab350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 71.166.62.12 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1894 Lines: 41 On Thu, 15 Jul 2010, Hagen Paul Pfeifer wrote: > * David Miller | 2010-07-14 14:55:47 [-0700]: > > >Although section 3 of RFC 5681 is a great text, it does not say at all > >that increasing the initial CWND would lead to fairness issues. > > Because it is only one side of the medal, probing conservative the available > link capacity in conjunction with n simultaneous probing TCP/SCTP/DCCP > instances is another. > > >To be honest, I think google's proposal holds a lot of weight. If > >over time link sizes and speeds are increasing (they are) then nudging > >the initial CWND every so often is a legitimate proposal. Were > >someone to claim that utilization is lower than it could be because of > >the currenttly specified initial CWND, I would have no problem > >believing them. > > > >And I'm happy to make Linux use an increased value once it has > >traction in the standardization community. > > Currently I know no working link capacity probing approach, without active > network feedback, to conservatively probing the available link capacity with a > high CWND. I am curious about any future trends. A long, long time ago, I suggested a Path BW Discovery mechanism to the IETF, analogous to the Path MTU Discovery mechanism, but it didn't get any traction. Such information could be extremely useful to TCP endpoints, to determine a maximum window size to use, to effectively rate limit a much stronger sender from overpowering a much weaker receiver (for example 10-GigE -> GigE), resulting in abominable performance across large RTT paths (as low as 12 Mbps), even in the absence of any real network contention. -Bill -- 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/