From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-03-ewr.dyndns.com (mxout-078-ewr.mailhop.org [216.146.33.78]) by lists.bufferbloat.net (Postfix) with ESMTP id CA55B2E0271 for ; Mon, 14 Mar 2011 13:24:42 -0700 (PDT) Received: from scan-02-ewr.mailhop.org (scan-02-ewr.local [10.0.141.224]) by mail-03-ewr.dyndns.com (Postfix) with ESMTP id C3548788313 for ; Mon, 14 Mar 2011 20:24:41 +0000 (UTC) X-Spam-Score: -1.0 (-) X-Mail-Handler: MailHop by DynDNS X-Originating-IP: 209.85.161.43 Received: from mail-fx0-f43.google.com (mail-fx0-f43.google.com [209.85.161.43]) by mail-03-ewr.dyndns.com (Postfix) with ESMTP id 53BFD787D86; Mon, 14 Mar 2011 20:24:41 +0000 (UTC) Received: by fxm3 with SMTP id 3so4150138fxm.16 for ; Mon, 14 Mar 2011 13:24:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:subject:from:to:cc:in-reply-to:references :content-type:date:message-id:mime-version:x-mailer :content-transfer-encoding; bh=yGZr5uryOltN1nlZ0Ciqma0STV2YVIGt+Osl4omI68k=; b=vnBI1WAtHSKOSMH41aoX002ELSqls3IUV5k4ZnfSH6Ju1/pq+SB/HhCDe9VaP1AVIC 59/ZOicBz1xBkQ8rcRMD96mAOnEKFqSlHYmlRk4KMdx/AhuiIEPxjh6ac52Ntk+CmA8+ BOxGf6f2hpUUuROGGRKgGUJt5tNgtrrx2ztdA= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:in-reply-to:references:content-type:date :message-id:mime-version:x-mailer:content-transfer-encoding; b=bw6eAVMiSkwiwJx2RDYZSRUcb1NZRB1vgSHHyS+aCPYObn1s3oG+xw1FPQdR5fv2NG f4ZXoX9mjsvOtNjoULloWYmEgVfbStQlxeH2iMm5NwxE2UD2xvRq+D9F+58D3QD0ONZ0 aiLzNL+y6uzaWoZ7UQQCKNq0g7wTFE94EfZC0= Received: by 10.223.127.210 with SMTP id h18mr2698810fas.73.1300134280526; Mon, 14 Mar 2011 13:24:40 -0700 (PDT) Received: from [10.150.51.211] (gw0.net.jmsp.net [212.23.165.14]) by mx.google.com with ESMTPS id 21sm7441fav.17.2011.03.14.13.24.38 (version=SSLv3 cipher=OTHER); Mon, 14 Mar 2011 13:24:39 -0700 (PDT) From: Eric Dumazet To: Jonathan Morton In-Reply-To: <5BC42741-852B-4699-BA5D-D70B8D610D96@gmail.com> References: <87wrk1a4gx.fsf@cruithne.co.teklibre.org> <5BC42741-852B-4699-BA5D-D70B8D610D96@gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 14 Mar 2011 21:24:37 +0100 Message-ID: <1300134277.2649.19.camel@edumazet-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Cc: netdev , bloat-devel , bloat Subject: Re: [Bloat] shaper team forming up X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 14 Mar 2011 20:24:43 -0000 Le lundi 14 mars 2011 à 21:55 +0200, Jonathan Morton a écrit : > On 14 Mar, 2011, at 9:26 pm, Dave Täht wrote: > > > Over the weekend, Dan Siemons uncovered a possible bad interaction > > between ECN and the default pfifo_fast qdisc in Linux. > > > > http://www.coverfire.com/archives/2011/03/13/pfifo_fast-and-ecn/ > > This seems to be more complicated that it appears. It looks as though > Linux has re-used the LSB of the old TOS field for some "link local" > flag which is used by routing. > > It's not immediately obvious whether pfifo_fast is using this new > interpretation though. If it isn't, the fix should be to remove the > RTO_ONLINK bit from the mask it's using on the tos field. The other > half of the mask correctly excludes the ECN bits from the field. > CC netdev, where linux network dev can take a look. I would say that this is a wrong analysis : 1) ECN uses two low order bits of TOS byte 2) pfifo_fast uses skb->priority skb->priority = rt_tos2priority(iph->tos); #define IPTOS_TOS_MASK 0x1E #define IPTOS_TOS(tos) ((tos)&IPTOS_TOS_MASK) static inline char rt_tos2priority(u8 tos) { return ip_tos2prio[IPTOS_TOS(tos)>>1]; } No interference between two mechanisms, unless sysadmin messed up things (skb_edit)