From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.toke.dk (mail.toke.dk [IPv6:2001:470:dc45:1000::1]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 19DF53B2A4 for ; Wed, 2 May 2018 12:16:01 -0400 (EDT) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=toke.dk; s=20161023; t=1525277759; bh=wmGqk7OKFUhWZmql/29WEZGahCoOkNyP8s5ePi7DPFg=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=ABExFjy9drgcx1We49LkpAVQ6Fp+GHMeDbLO6pr2KXVMGX1siFkLpOLyPeeo1IAmu GstpBEV9ObUcNqoSbc0X2QlQ2A9hmpiznuKFGUO5IsebBCmd4QUw5o0q0NvYNOXoHH 9cOXTDn3qrGnZyJ9YQ4IktwRv6jl8A9YQTlFskPDfYd1tMV7qCPaN650PAv8lMpebe T5ePtqYTCvehYGPDZ3FzsDL0u4yfJW9bDmxcWgAZSQEG6388+JJrys0ZQgfAbLA2l6 HoeIw2jnbJLR9oC3iW5xmvXQvCtF+bti5thdIJPjEeV3/2RxzZMgv/0TcjY8AvvYjq pLd+2d+eg4k0g== To: Sebastian Moeller Cc: Cake List In-Reply-To: <6CAF0E83-68A8-450B-9C78-F00C81B037A4@gmx.de> References: <152527385803.14936.8396262019181995139.stgit@alrua-kau> <152527388834.14936.16168261814447709834.stgit@alrua-kau> <7A6AB93A-565B-4251-B0A8-90631A9A152B@gmx.de> <87k1sm13e1.fsf@toke.dk> <6CAF0E83-68A8-450B-9C78-F00C81B037A4@gmx.de> Date: Wed, 02 May 2018 18:15:59 +0200 X-Clacks-Overhead: GNU Terry Pratchett Message-ID: <87efiu11a8.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Cake] [PATCH net-next v7 6/7] sch_cake: Add overhead compensation support to the rate shaper X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 02 May 2018 16:16:01 -0000 Sebastian Moeller writes: > Hi Toke, > > > >> On May 2, 2018, at 17:30, Toke H=C3=B8iland-J=C3=B8rgensen wrote: >>=20 >> Sebastian Moeller writes: >>=20 >>>> On May 2, 2018, at 17:11, Toke H=C3=B8iland-J=C3=B8rgensen wrote: >>>>=20 >>>> + /* The last segment may be shorter; we ignore this, which means >>>> + * that we will over-estimate the size of the whole GSO segment >>>> + * by the difference in size. This is conservative, so we live >>>> + * with that to avoid the complexity of dealing with it. >>>> + */ >>>> + len =3D shinfo->gso_size + hdr_len; >>>> + } >>>=20 >>>=20 >>> Hi Toke, >>>=20 >>> so I am on the fence with this one, as the extreme case is having a >>> super packet consisting out of 1 full-MTU packet plus a tiny leftover >>> in that case we pay a 50% bandwidth sacrifice which seems a bit high. >>> Nowm I have no real feling how likely this full MTU plus 64 byte >>> packet issue is in real life, but in the past I often saw maximum >>> packetsizes of around 3K bytes on my router indicating that having a >>> sup packet consisting just out of two segments might not be that rare. >>> So is there an easy way for me to measure the probability of seeing >>> that issue? >>>=20 >>> I am all for sacrificing some bandwidth for better latency under load, >>> but few users will be happy with a 50% loss of bandwidth... >>=20 >> Well, in most cases such GSO segments will be split anyway (we split if >> <=3D 1 Gbps). So this inaccuracy will only hit someone who enables the >> shaper *and sets it to a rate rate > 1Gbps*. Which is not a deployment >> mode we have seen a lot of, I think? > > Oh, I agree with that rationale; I was still under the impression that > we want to go back to a (configurable) serialization delay based > segmentation threshold and then this might become an issue (especially > on puny routers will profit from the reduced routing cost* of > GSO/GRO). Also I fear that 1Gbps service will become an issue rather > sooner than later, even though I would assume that then dual segment > super-packets should really be rare... Sure, let's go back and revisit if and when we do that :) -Toke