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 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 6A0C721F5A2 for ; Mon, 2 Nov 2015 03:23:13 -0800 (PST) Received: from u-089-d061.biologie.uni-tuebingen.de ([134.2.89.61]) by mail.gmx.com (mrgmx001) with ESMTPSA (Nemesis) id 0LqQnR-1aNt7P3uJl-00e46Q; Mon, 02 Nov 2015 12:23:10 +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 12:23:13 +0100 Content-Transfer-Encoding: quoted-printable Message-Id: <631AA4E6-6447-4E0D-9CA4-5500E1263CF5@gmx.de> References: To: Kevin Darbyshire-Bryant X-Mailer: Apple Mail (2.1878.6) X-Provags-ID: V03:K0:8CKAp1Vs51isRNPWSgDicQJ3+I92COK+6ZX9ddc/BUsyNDkuiVE 676+nu1n8ymKkzpPM68xEILaIAc9uUxWOJhWvdVCblkeq65eZF8Q1fD2retSQ+duY4yu5/v GM+6ulItydOXQpIHK0A0icTbHAa+bg2dvNxUJSeCishh1VexwJ6xMwNjFnZrpeWQfiLvJSb LpDJ4MyORjfhYNUGl30Dw== X-UI-Out-Filterresults: notjunk:1;V01:K0:e7sf+qNfMZ0=:U69j87IF702XxncyuDsslv qK27dvRqEU7iWnHZA1ECZvdVqfOrP2GBorT9k9sknt2peWoxlVkqONM8SPbq4R8+pIQeOEC69 6TYHUMpKYH2T/Xw1ew8lu2b0w++VqGTwx0Ien4qCwj0VYYZ01J1DrwQTd04SOwBpcNg5YzIkE z5KXBuOz6hKzBIVDrCIyb2QvSUacddnjZZvTQ4vXGO6+uz3EI3r+1Uwh5Pq15PmAgBvENmsHj lf0fwFR82c0wpbL5+FnvwXuZCijB44ju2aJjkM/heyLcp3daDLGKP/6nozXKqY0MyQxTHapIv 1WUD31ut0eMzIC6r71t1rR4+pA8m4BAXRyhT8mjcyo14/2q9YbeDf3lamy/ftC7ABRe8sywem XIZ5SgGfZY44MTHuEGz62caj+Hw62NJzCnhDBufIgAPF8WRAjhOGo6ksbemE9GI+uRgdKIcaX 7P9oimF2x24b/TA9DvFBFvGMrjxOETE3opz9bLHRX/p4B6FRfgQ4rivbLyPzSECSAahQkq57A 9+BvRxi8/CT26ASkpUme0Zfx05WphhVBavsUX2FEc6Wql4JkEzYRQwSE0aWbSLVnIE8r1YLkJ g4UKuca4gXg2jvCrLO79cRpcYPatbmtTTKWfnQp99G9dNUHQu25Ca6hIuWGbBJrlYRY+iJJAG ZFbMeYGDZbN+WNme1LZpSonlOtCYCZ/hm0B6POmUDfD30nmNiECTH0OlQru8mprOiG+SvNmye KlPw+DCAZpOgAzAa6zWwvskrDfjDuvKhnX2TVENOIkyxGORKfBXsaD7k7noWkt65gcuHvDsjT YG4jxT1 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 11:23:36 -0000 Hi Kevin, On Nov 1, 2015, at 22:52 , Kevin Darbyshire-Bryant = wrote: >=20 > Can't give full explanation now but the bytes per ns calculation which = is used as a basis for target on 'slow' links uses mtu*1.5 Which has the advantage of being larger than ATM encapsulation = expansion would account for so this is on the safe side=85 Best Regards Sebastian >=20 > -- > Cheers, >=20 > Kevin@Darbyshire-Bryant.me.uk >=20 >> On 1 Nov 2015, at 20:58, Alan Jenkins = wrote: >>=20 >>> On 01/11/2015, Sebastian Moeller wrote: >>> Dear cake committee, >>>=20 >>> I just played around with the most recent sch_cake and noticed us: >>>=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 :). >>=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. >>=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). >>=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 >>=20 >> Warm regards >> Alan >> _______________________________________________ >> Cake mailing list >> Cake@lists.bufferbloat.net >> https://lists.bufferbloat.net/listinfo/cake