From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail2.tohojo.dk (mail2.tohojo.dk [77.235.48.147]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id 2B0A421F24E for ; Tue, 3 Nov 2015 04:46:53 -0800 (PST) X-Virus-Scanned: amavisd-new at mail2.tohojo.dk DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=toke.dk; s=201310; t=1446554810; bh=+wQ9obdaCan8Mdkm7aLwMAcYch/WJ3KggvdEP75AIBI=; h=From:To:Cc:Subject:References:Date:In-Reply-To; b=olZfS3nFe9X01jrZ8tMdrAR9Cq7ch0rhizVQZ+idspqZnZaaq/C86/qtFsVyIErNl A+wI8F71Ah3zanTacXKOTmlyE9ahSUMy3wjFS3Ny7xpUD+Nz3TunFoPHQ88vyekG30 +POyyHRKdSn6wTVuZs0JOlYtP1EX+8xT32clguJQ= Received: by alrua-kau.kau.toke.dk (Postfix, from userid 1000) id B41AFC402B3; Tue, 3 Nov 2015 13:46:49 +0100 (CET) From: =?utf-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= To: Kevin Darbyshire-Bryant References: <5638A4F4.2010701@darbyshire-bryant.me.uk> Date: Tue, 03 Nov 2015 13:46:39 +0100 In-Reply-To: <5638A4F4.2010701@darbyshire-bryant.me.uk> (Kevin Darbyshire-Bryant's message of "Tue, 3 Nov 2015 12:13:40 +0000") X-Clacks-Overhead: GNU Terry Pratchett Message-ID: <87si4nntcg.fsf@toke.dk> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Cc: cake@lists.bufferbloat.net Subject: Re: [Cake] More on 'target' corner cases - rate/target/interval confusion? 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: Tue, 03 Nov 2015 12:47:16 -0000 --=-=-= Content-Type: text/plain Kevin Darbyshire-Bryant writes: > Can someone please explain if the above is actually correct and why. > i.e. I'm confused why voice traffic has a target latency of 72mS over > a measurement interval of 1/2 second when I'd have thought keeping > voice latency as low as possible would be the ideal. I'm sure I'm > being exceptionally stupid so I await education please :-) Well, I *think* this comes from the 1.5*MTU calculation. I.e. 1.5 * 1500 bytes at 250Kbps is 72 ms. And interval is adjusted to always be 8*target. Now whether or not this is *correct* I'm not so sure about. The minimum value set from the MTU is the Linux counterpart to the CoDel NS2 model's "always keep one packet in the queue". The reasoning is, basically, that there will be at least one packet in the layers below the qdisc which we will have to wait for before we can dequeue; so CoDel shouldn't react until queueing time goes *above* this minimum of waiting for one packet. Now, in this case we have the rate limiter built right in to the qdisc, so the queued packet will in fact *not* be in a layer below (because that is probably going to be a link with a physical rate that is quite a bit higher than what we're setting here; or if not, we're not doing the MTU adjustment anyway). So it's not quite clear to me what the right thing to do here is; as you rightly point out this leads to a very high target for the VoIP queue which is not necessarily a good idea. Capping the target before doing the per-tin calculation might be a better idea (i.e. using the total bandwidth limit as the input to the calculation). Will think about it some more. -Toke --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAEBCAAGBQJWOKyvAAoJEENeEGz1+utPIyEH/0t40MbuFYv6D7gfYwXUgODd r2lLH4ctveocKBXAiPMISxKKJtl9nVf3TBp7vjjrz18qIihAH4RGCnby0CO00dPr TH5ThDK+XjojICcaRQ4UkGGZcCrYh1aBfB3E+aO/Whl5YLRPZKqIn3fbXpompWIG MxtKIZRMOdTUSGz/gVNjNQ69jv2ZHRbBtWnax+0E8hygTplh5QNiQ9NpVF6abZWV UJvTN7zuL0De5EGc+bZ7BiLDCzdbwpsjOQfSK0BsZsMI8TjBpjT97o+Ho/Fa/kKP VTq2iYZcpnleOsBnH+LOwMVxdOvAor9GYxnv5l4hxOQqIihY6eHIZ4MeolB/jk8= =fAuC -----END PGP SIGNATURE----- --=-=-=--