Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967148Ab0GSWvQ (ORCPT ); Mon, 19 Jul 2010 18:51:16 -0400 Received: from mail-vw0-f46.google.com ([209.85.212.46]:63681 "EHLO mail-vw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966620Ab0GSWvP convert rfc822-to-8bit (ORCPT ); Mon, 19 Jul 2010 18:51:15 -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=kbPGYjOvZeRPLhlvxohUR5NcRzZzQYT+VLa6G5Fd+6qm30h1nbeRExl4cJZgYPwPoa lkVMr8YaKs9X1RLQ2SHWZdIqeyxSWy8jbuJcqN2oNuJ6adzs/n2fN93GVnDcxsYpRUv4 uZClDHaioUPkEDMkDGPD/W5HjYlw4FFIRMEZU= MIME-Version: 1.0 In-Reply-To: <4C448688.1070507@hp.com> References: <4C3D94E3.9080103@wildgooses.com> <4C3DD5EB.9070908@tmr.com> <20100714.111553.104052157.davem@davemloft.net> <1279299709.2156.5814.camel@tng> <4C448688.1070507@hp.com> Date: Mon, 19 Jul 2010 15:51:13 -0700 Message-ID: Subject: Re: Raise initial congestion window size / speedup slow start? From: "H.K. Jerry Chu" To: Rick Jones Cc: Patrick McManus , David Miller , davidsen@tmr.com, lists@wildgooses.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: 2036 Lines: 50 Mon, Jul 19, 2010 at 10:08 AM, Rick Jones wrote: > H.K. Jerry Chu wrote: >> >> On Fri, Jul 16, 2010 at 10:01 AM, Patrick McManus >> wrote: >>> >>> can you tell us more about the impl concerns of initcwnd stored on the >>> route? >> >> >> We have found two issues when altering initcwnd through the ip route cmd: >> 1. initcwnd is actually capped by sndbuf (i.e., tcp_wmem[1], which is >> defaulted to a small value of 16KB). This problem has been made obscured >> by the TSO code, which fudges the flow control limit (and could be a bug >> by >> itself). > > I'll ask my Emily Litella question of the day and inquire as to why that > would be unique to altering initcwnd via the route? > > The slightly less Emily Litella-esque question is why an appliction with a > desire to know it could send more than 16K at one time wouldn't have either > asked via its install docs to have the minimum tweaked (certainly if one is > already tweaking routes...), or "gone all the way" and made an explicit > setsockopt(SO_SNDBUF) call? ?We are in a realm of applications for which > there was a proposal to allow them to pick their own initcwnd right? ?Having Per app setting of initcwnd is just one case. Another is per route setting of initcwnd basis through the ip route cmd. For the latter the initcwnd change is more or less supposed to be transparent to apps. This wasn't a big issue and can probably be easily fixed by initializing sk_sndbuf to max(tcp_wmem[1], initcwnd) as you alluded to below. It is just our experiements got hindered by this little bug but we weren't aware of it sooner due to TSO fudging sndbuf. Jerry > them pick an SO_SNDBUF size would seem to be no more to ask. > > rick jones > > sendbuf_init = max(tcp_mem,initcwnd)? > -- 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/