Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753784Ab1ETMjF (ORCPT ); Fri, 20 May 2011 08:39:05 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:50771 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751725Ab1ETMjD (ORCPT ); Fri, 20 May 2011 08:39:03 -0400 Date: Fri, 20 May 2011 13:37:47 +0100 From: Alan Cox To: Hagen Paul Pfeifer Cc: "H.K. Jerry Chu" , David Miller , , , , , , , , Subject: Re: [PATCH] tcp: Expose the initial RTO via a new sysctl. Message-ID: <20110520133747.2b8fb2b0@lxorguk.ukuu.org.uk> In-Reply-To: References: <1305715384-81716-1-git-send-email-tsunanet@gmail.com> <20110518.152653.1486764697527722925.davem@davemloft.net> <20110518.155200.801089483916944725.davem@davemloft.net> <20110518202025.GC4175@nuttenaction> X-Mailer: Claws Mail 3.7.8 (GTK+ 2.22.0; x86_64-redhat-linux-gnu) Face: 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 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1644 Lines: 30 > For our environment it hurts because we _always_ have an initial RTO >1. I > understand and accept that 98% will benefit of this modification, no doubt > Jerry! Try to put yourself in our situation: imaging a proposal of an init > RTO modification to 0.5 seconds. Maybe because 98% of Internet traffic is > now localized and the RTO is average now 0.2 seconds. Anyway, this will > penalize your network always and this will be the situation for one of my > customer. I can live with that, I see the benefits for the rest of the > world. But I am happy to see a knob where I can restore the old behavior. > Maybe some other environments will benefit from a even lower or higher > initial RTO. AX.25 is definitely happier with a multi-second round trip but it's a special case. Some X.25 networks are going to have similar behaviour. It shouldn't be penalising each connection (and it's worse than that of course because each node on a shared media network gets in the way of the rest, plus the queueing effect of all the extra blockages) because done right multiple connections to the same host can use the previous connections as estimates (and indeed for the initial RTO there's a good argument for treating estimates as 'host, then x.y.z.* match, then average of previous except the x.y.z.* match, then unknown') The latter would fix an awful lot of the weird cases pretty effectively. Alan -- 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/