From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailout-de.gmx.net (mailout-de.gmx.net [213.165.64.23]) by huchra.bufferbloat.net (Postfix) with SMTP id C3B7421F0C3 for ; Sun, 5 Aug 2012 10:04:09 -0700 (PDT) Received: (qmail invoked by alias); 05 Aug 2012 17:04:08 -0000 Received: from unknown (EHLO srichardlxp2) [213.143.107.142] by mail.gmx.net (mp071) with SMTP; 05 Aug 2012 19:04:08 +0200 X-Authenticated: #20720068 X-Provags-ID: V01U2FsdGVkX18gGYV0B3sgnYpTq7Irq2+7XhlX1SEyGz1i7t/Rsw S9IQOS8/i3leyj Message-ID: <4A256974B5054317913BC067C4E5FAE1@srichardlxp2> From: "Richard Scheffenegger" To: "Eric Dumazet" , "Andrew McGregor" References: <1344048299-26267-1-git-send-email-dave.taht@bufferbloat.net><1344062738.9299.1453.camel@edumazet-glaptop><501D99C4.20902@pollere.com><7EB59257-1A8E-4567-8AD3-5016594565CC@gmail.com> <1344144623.9299.1557.camel@edumazet-glaptop> Date: Sun, 5 Aug 2012 18:54:34 +0200 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5931 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 X-Y-GMX-Trusted: 0 Cc: codel@lists.bufferbloat.net Subject: Re: [Codel] [RFC PATCH] codel: ecn mark at target X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 05 Aug 2012 17:04:10 -0000 Hi Eric, ----- Original Message ----- From: "Eric Dumazet" To: "Andrew McGregor" Cc: Sent: Sunday, August 05, 2012 7:30 AM Subject: Re: [Codel] [RFC PATCH] codel: ecn mark at target > On Sat, 2012-08-04 at 20:06 -0700, Andrew McGregor wrote: >> Well, thanks Eric for trying it. >> >> Hmm. How was I that wrong? Because I was supporting that idea. >> >> Time to think. > > No problem Andrew ;) > > Its seems ECN is not well enough understood. > > ECN marking a packet has the same effect for the sender : reducing cwnd > exactly like a packet drop. Only difference is avoiding the > retransmit[s]. That's true for the first mark; any subsequent mark (during the same window) should have no effect - thus a high marking rate (marking fraction per window) should not be that much worse... Of course, the queue can never know the effective window of the tcp stream it is marking... As a test, when the marking is done really instead of drop, do you see fairness betwenn the ecn and legacy tcp flows? (if not, the ecn implementation may be faulty). > > It cannot be used only to send a 'small' warning, while other competing > non ECN flows have no signal. > > As far as packet schedulers are concerned, there should be no difference > in ECN marking and dropping a packet. I believe linux packet schedulers > are fine in this area. > > Now, there are fundamental issues with ECN itself, out of Codel scope, > thats for sure. > > How widely has been RFC 3540 deployed, anybody knows ? Virtually not; even if the end hosts negotiate ECN, the network doesn't do any marking (rendering ecn mood). See Bauer and Beverly, "Measuring the current state of ECN support in server, clients, and routers", http://mirrors.bufferbloat.net/Talks/AIMS2011/bauer-ecn-aims-2011.pdf > > > > _______________________________________________ > Codel mailing list > Codel@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/codel