Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932449Ab0GOF30 (ORCPT ); Thu, 15 Jul 2010 01:29:26 -0400 Received: from mail-vw0-f46.google.com ([209.85.212.46]:45030 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932267Ab0GOF3Y convert rfc822-to-8bit (ORCPT ); Thu, 15 Jul 2010 01:29:24 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=V8xbL6OID1/5AOf1rSYhEfeR/lYIaphfM6aUoaxNFIz1zGygRoiRjrObWUnBna1k67 cyhRTDZ/4O0zari70knBnEdyjvkA8RyQJVz6holXDCMMDi6L1Gmt+KYsmt9OVdMgRomX PU8Q7b3lD4XLdrQLk2UFj04R1/v64Sz2e7zfM= MIME-Version: 1.0 In-Reply-To: <20100714234917.924f420d.billfink@mindspring.com> References: <4C3E0684.5060409@wildgooses.com> <4C3E1B54.40604@hp.com> <20100714203919.GD6682@nuttenaction> <20100714.145547.102555471.davem@davemloft.net> <20100714221301.GI6682@nuttenaction> <20100714234917.924f420d.billfink@mindspring.com> Date: Wed, 14 Jul 2010 22:29:21 -0700 Message-ID: Subject: Re: Raise initial congestion window size / speedup slow start? From: "H.K. Jerry Chu" To: Bill Fink Cc: Hagen Paul Pfeifer , David Miller , rick.jones2@hp.com, lists@wildgooses.com, davidsen@tmr.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2465 Lines: 54 On Wed, Jul 14, 2010 at 8:49 PM, Bill Fink wrote: > 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. Unfortunately that is not going to help initcwnd (unless one can invent a PBWD protocol from just 3WHS), and the web is dominated by short-lived connections so the small initcwnd becomes a choke point. Jerry > > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?-Bill > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at ?http://vger.kernel.org/majordomo-info.html > -- 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/