From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.15.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 38BDD3B2A4 for ; Wed, 2 May 2018 12:08:35 -0400 (EDT) Received: from [172.16.11.125] ([134.76.241.253]) by mail.gmx.com (mrgmx001 [212.227.17.190]) with ESMTPSA (Nemesis) id 0M9sa0-1f2slE474q-00B3B0; Wed, 02 May 2018 18:08:33 +0200 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.3 \(3445.6.18\)) From: Sebastian Moeller In-Reply-To: <87k1sm13e1.fsf@toke.dk> Date: Wed, 2 May 2018 18:08:31 +0200 Cc: Cake List Content-Transfer-Encoding: quoted-printable Message-Id: <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> To: =?utf-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= X-Mailer: Apple Mail (2.3445.6.18) X-Provags-ID: V03:K1:lmlDSPTLXkt0eGEKmHMviWMVWLGvI9lUq1pdwluPKAkfLcNXDyG GNO8XbAl7QZaO45L4CWLepgH1XqdaGeP/AndHMwd6Qg5R7yImh9SHJ/gu9LkaM7OGcFYRE2 hkqnOyXPA/IwckDfjBhFv/rFCVFtFXsl/NHyXORg3+JVZypUjrN3aNCKM/TcPjaNVgNfoEL ZOKDCWzrJncaPlGUZq17g== X-UI-Out-Filterresults: notjunk:1;V01:K0:WBiAeStVC9U=:GLG9OX33E1CNVAtQOglGoh G3yG59/wTyllPZsovIuoSQVd/tw/DBK2CashAcGyBYDtRzrRfLLpRJO0OGl+z+8zDhG8IR6TD O6tnowGF0/FUWGzoh99bY45nfvgdMwYtnJqybyqqdn6Kecr+9z2V9ToIClLkWcmUJ++51o0FD KtGp2Yo3ODAy6Enacokqh6T0Pi927IfxY4x2937Awl6Q3sp8gWFPx9gjsOtwEIyWZ2Df85e9k rFp+F+6Y5fWLkRe4Ro4QDH4C3S+SsXNX6vmk0ea7JFNHCTbqyvZ5nVE06C88197WxDdlBl5F2 t95M7vZxTjv+8AUjAcBF5v6dxfefli/IkCqgyVDkTU/nDt3r6E2IY8YBfmusRm+ZIvxy8EgQJ SPkPpBosjtz0GvdIycwzBQViWgmqTrnMDdwbFcFziMGCEGRgmbl7ZX97bollECEEsXDreW67R swZ9wdUM30O5UnT5e3qG98ostyfAT1uKFncvo/n3Vam0vvFU0kUgpXRZNY8tyrFBYFVS6AxAI OyCquvUCU7lF4Q7i2jTV45R1vE6gQ62NfRJct6Ia+An8x3M/etsugChMNDKmVHDctkSpLZtvf 4xX57A/88vAq4sJUr498OMHEqwlfSd7azRPv7AdPcGs/cSSSJeeOyQiZ6dNkQsWNwlt5BBqFG BmOzNfV3ZEDxSSwiyLBSUgYVtfAeOfjBoKL6PW2uY/92N4RNWF+cK3QxO6M8XqELjiHV/28nT 0xPkbiopFg16JOHFHiWihp2zbe3AiO7HNnzl6LjoxmgI4RWu4feCRnAW0CGTTtH9pbL0i+s7r cnswJKA 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 16:08:35 -0000 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... >=20 > 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 ;) Again, I agree without proof that this is more than a = theoretical issue, let's ignore this for now (especially since this is = going to interfere with ATM encapsulation, but on ATM the bandwidth = should always merit a segmentataion of supers (sorry, ISPs cake is not = designed as the customer facing shaper on the DSLAM ;) )) Best Regards Sebastian >=20 > -Toke *) I guess the kernel's routing codsts pales in comparison with the = actual shaping cost, so this might be a bad idea.=