From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.15.19]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mout.gmx.net", Issuer "TeleSec ServerPass DE-1" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id D271121F52F for ; Mon, 2 Nov 2015 03:29:42 -0800 (PST) Received: from u-089-d061.biologie.uni-tuebingen.de ([134.2.89.61]) by mail.gmx.com (mrgmx002) with ESMTPSA (Nemesis) id 0MBFgr-1Zj4oj0XVV-00AE5y; Mon, 02 Nov 2015 12:29:40 +0100 Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) From: Sebastian Moeller In-Reply-To: Date: Mon, 2 Nov 2015 12:29:42 +0100 Content-Transfer-Encoding: quoted-printable Message-Id: <2BF7D1AC-1D4B-48BD-AA67-D58A2F997916@gmx.de> References: To: Alan Jenkins X-Mailer: Apple Mail (2.1878.6) X-Provags-ID: V03:K0:WwRDpNkPykESMbZqag+mEoCNu4HOx1s0U0ofiYbLMyeihdGW1T2 nAjsAm5WbC7w6ay2OdIxGuXSCCL4LzUv5KgEiF9MIdjzlgg+BS+shAPRTLdBA2K0ioRdB58 Sxv4HmlnLcLH0Av2VYwtQiunphKRNmjA3Ci/INF6FWCmNnKXHqtXkxhB/Q3RQndH9x/UBw7 7i9N3d9t3heuKwhZsz2aw== X-UI-Out-Filterresults: notjunk:1;V01:K0:kX6tjKsJd6g=:SFFEYqBI6n3KlksP4yi4Qx Rwu6rIlPxN9DVROuyxNdiGWOMGJbaTR16VgNDKmBlVGUZyKK8fscse064Qxm68XsZsZoOfX/B 5VTlYElVwlaDuzX7iEQ7UqhdbtaNuDBaKf6rX5PgooLkyN8t76QWUi0XwRGlemzjp4l7TIbWR RleNRIC3F6I5eI66nN2BQBf1bJtR1WQOpfbn/6pqA961ePy4nT0jm0054Crp2rVr8RMLGo4V8 mH44pn/JgMRsmjoRfHhr6pgUeTg2uXzGkgNzjutrgDwBsqu4Q9zcrpqnKR/z10lM36vVpNve5 yFkUBIpxZdS6GZgqdNZvNzWwQKvtEqQb7uEixAY7julAcCSY2NzVa32DKNeMmuMpLQYE6yRK8 42qar5+rF2w2FNq/IbwOCAL0CZzVbbeYhJeTjLwm656T1cPnkfCAXi+SMmEte7JipROmHv7aN AHjPCdh1FiZ78+0Dyy7eRcyMbN18wEXjw7U39mPHXWqk349EY2Q09BuhwH/qbtfyFYWJh6oXW 5RnEzYy9YZStIXkuJ+txY35tAhWN9IZXtSUrbR4UJpQhOPc/4akmvjQbU1RAfWHf6oWu6UVsR PzeMAvfHfX0uFi4MaQ4nsx/GRkgOnQp3/IsdpS11sKxV14ckEhCALl56iGxFdb9778mCNmRqa Pf5RD5cyNr5feq4QIx696y8ECskzezghbS+vuz+kIHB/I9x0CjzvS9GK55zuI2pHH1JQd/lLU mx48FNvYUdt5Tm4sjyD3ISA+w6tSK2gU5/hNls8XlCK+QYxJwOqy+FGKgmwufFzopU4OHoZvk XDmeyoI Cc: cake@lists.bufferbloat.net Subject: Re: [Cake] cake target corner cases? X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 02 Nov 2015 11:30:05 -0000 Hi Alan, On Nov 1, 2015, at 21:58 , Alan Jenkins = wrote: > On 01/11/2015, Sebastian Moeller wrote: >> Dear cake committee, >>=20 >> I just played around with the most recent sch_cake and noticed: >>=20 >> user@computer:~/CODE/tc-adv/tc> sudo tc-adv qdisc del dev eth0 root >> user@computer:~/CODE/tc-adv/tc> sudo tc-adv qdisc replace dev eth0 = root cake >> bandwidth 1Mbit ; sudo tc-adv -s qdisc >> qdisc cake 8005: dev eth0 root refcnt 6 bandwidth 1Mbit diffserv4 = flows rtt >> 100.0ms raw >> Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0) >> backlog 0b 0p requeues 0 >> capacity estimate: 1Mbit >> Tin 0 Tin 1 Tin 2 Tin 3 >> thresh 1Mbit 937504bit 750Kbit 250Kbit >> target 18.2ms 19.4ms 24.2ms 72.7ms >> interval 145.3ms 155.0ms 193.8ms 581.4ms >=20 >=20 >> Here target is always 12.5% of interval instead of the expected 6.25% >> 1/16 =3D 0.0625 >> 72.7/581.4 =3D 0.125042999656 >> 24.2/193.8 =3D 0.124871001032 >> 19.4/155.0 =3D 0.125161290323 >> 18.2/145.3 =3D 0.125258086717 >> But the bandwidth is really low, so pushing target closer to the = bandwidth >> conserving side of the codel rationale might be fine, >=20 > Pretty sure it's a minimum derived from the MTU >=20 > ((mtu=3D1.5kbyte) * 8 bits/byte) / 1000 Mbit/s =3D 0.012s >=20 > except I don't know where the .5 comes from, that's incredibly > suspicious to have a round 1/8th :). As we agree later/earlier 1/8th it is ;) >=20 > The point is that if buffering falls below the MTU, the connection > will be completely clobbered. >=20 > In a way it's nice cake reports this in the target. Otherwise cake > would claim the target is 5ms, but measurements would show the > effective target is more than twice as high. >=20 >> since latency is bad >> to begin with and bandwidth also pretty scarce. But it might be = interesting >> to do a few more measurements at low bandwidths to confirm that the = 12.5% of >> interval logic holds water; one could also argue that people with = such links >> (a lot of DSL lines have even less upload, so this certainly is not = extreme) >> might think that any added ms of delay matters (more than bandwidth); >> currently we leave the user no remedy... >>=20 >>=20 >=20 > >=20 >> This looks okay, except Tin3 has target at 7.3/101.0 =3D = 0.0722772277228 7% of >> interval. >=20 > Looks like the same thing. Well, I believe there is a gradual shift from the default = 5ms/6.2ms target to the 1/8th target and this is just somewhere in = between, by virtue of the smallest bandwidth or so... >=20 >=20 >> Both observations might actually be on purpose, but if so we should = document >> that behavior as expected, for example in the man page=85 >>=20 >> Best Regards >> Sebastian >=20 >=20 > I'm afraid I can't help mention my old niggle :). _If_ you mention > this alongside instructions for RRUL, I think you'd also want to > explain^W mention the measurement increase for diffserv4 v.s. > besteffort. >=20 > I think the ICMP ping measurement increases by another 10ms on my > connection (11500k down / 850k up, so an mtu is ~15ms). I concluded > it was inherent in prioritization. Now I guess it's equal to the sum > of target * bandwidth_fraction for each class "above" icmp ping (and > could be tested). Well, with standard sqm-scripts (htb and fq_codel) we leverage = iptables to do the filtering, which comes with its own computation cost=85= then again with your bandwidths there should be enough cycles left to = do this... >=20 > I have graphs from sqm with and without classification. I did test > cake once and I think it's the same (otherwise would be a bug). >=20 > = https://dl.dropboxusercontent.com/u/49925445/bufferbloat.net/220-cdf-53141= 4.sqm_simplest_11500_850_atm40_udppingfix.svg >=20 > = https://dl.dropboxusercontent.com/u/49925445/bufferbloat.net/221-cdf-36050= 5.sqm_simple_11500_850_atm40_udppingfix.svg Yes, that is the picture I know, I believe cake looks a bit = different, by virtue of doing a few things in a more integrated, clever = way; not sure how it looks at low bandwidth though, I rarely test at low = bandwidth nowadays. Even though I should=85 Best Regards Sebastian >=20 > Warm regards > Alan