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 583203B2A4 for ; Wed, 2 May 2018 11:30:33 -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=1525275031; bh=R44xuaQs0qgu47SvgZPusocEW63sb9TCLxF7a8jxi1Q=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=Y28l8njEE7nwoPv+UcveMc5rvWWbbh/+xJQH07ZwsnD1vTZ+O1isNeCXUJMnzOzfU eUlr9yqNZQmXwueDVUgcA0u6ejBdYRgYkcBFTBUJQuEnIcjCBv7V0URthMbD3k6tDN YE7WpuffbWf1MghjFd//MGXEanNQrg/1M9wg9k0L8coWfVYKJPng0YHg0XjnzbnZ4S fSd4N9K3MiYlamYFzS6BGcJyKcH2vJ/w/bdx0AJ9ieecE2/nNiNS7H5HWY1CRNeRoc CZfMLq8EOpoaWHMb/KabB5G5NP1mRifJKGQVx0RYiqrG6lPo18H9YDDfytrKAdp+GR /GVbr56Rq2DIA== To: Sebastian Moeller Cc: Cake List In-Reply-To: <7A6AB93A-565B-4251-B0A8-90631A9A152B@gmx.de> References: <152527385803.14936.8396262019181995139.stgit@alrua-kau> <152527388834.14936.16168261814447709834.stgit@alrua-kau> <7A6AB93A-565B-4251-B0A8-90631A9A152B@gmx.de> Date: Wed, 02 May 2018 17:30:30 +0200 X-Clacks-Overhead: GNU Terry Pratchett Message-ID: <87k1sm13e1.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 15:30:33 -0000 Sebastian Moeller writes: >> 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; >> + } > > > Hi Toke, > > 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? > > I am all for sacrificing some bandwidth for better latency under load, > but few users will be happy with a 50% loss of bandwidth... 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? But sure, in principle you are right; I have no idea how to measure the probability, though. We could conceivably add another statistic, but, well, not sure it's worth it... I am certainly not going to do it ;) -Toke