From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.17.22]) (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 21A0F21F45E for ; Tue, 3 Nov 2015 03:08:20 -0800 (PST) Received: from u-089-d061.biologie.uni-tuebingen.de ([134.2.89.61]) by mail.gmx.com (mrgmx101) with ESMTPSA (Nemesis) id 0Lip2P-1aRoCr18IP-00cwTU; Tue, 03 Nov 2015 12:08:16 +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: <56388CA4.7000308@darbyshire-bryant.me.uk> Date: Tue, 3 Nov 2015 12:08:15 +0100 Content-Transfer-Encoding: quoted-printable Message-Id: <355718FB-BE85-4C53-BE85-48367A62B923@gmx.de> References: <87pozspckj.fsf@toke.dk> <6A2609D9-7747-487B-9484-ECC69C50DE96@gmx.de> <56388CA4.7000308@darbyshire-bryant.me.uk> To: Kevin Darbyshire-Bryant X-Mailer: Apple Mail (2.1878.6) X-Provags-ID: V03:K0:mVMqrRgnXtjZTb0qL8eoJOPtc2FnjtRF/hgNUk1FqvbHq4DNU3+ D/jneT2efP8prcMxhlxLKetmQ2uqppJl0HXpwZnhBdtv0fTVIuMMtSR8eFD4aweOzCzN4F4 vdks7M5BKBpwZnzQqqG/9eTGS3ZaEUhE6gA3FkKZiZz/hO3f5iRB7dUJPbNxq7R+NRWAbae 4ANThcd3ZG8WZibxo/0lA== X-UI-Out-Filterresults: notjunk:1;V01:K0:OzuPcjkwmhA=:IA9PZ3M0/pCh1106tjX9u/ U2j4wTXjAMgpgyGka0X30pWfM7l/wY5zUTe1yjd9tMJMnNYaC2PWpOZYa93wTQYXowMRKMGB1 jjl5MCGgpAjyPO1BmpAdGUWoAL6S4Ll4mijUyubOIwGTxZVHh3ejEEguKWj5Bp+AB5pNrantO k0RkG9IF+YZLJtJYeJQX2ACUvkUvubmos0lIsp9sRjppImzCPmLoo+G7ofCZGlMJMy7xe78mb KKycSnUe6WDUHcfciCqO1S8xoFmFE880gSyz3Lmi+k5C//U6Ao3K3FYsJnIwhGGW7UCfL0A81 oYxenfk6kvuMtQEjjlWCuqDzTDpYPtsnqnGPbBLtB3Ufszjuh5OmgYy6lg2ejoPl2ZZ2vLZkc 9gSzkek0Mkj7Vdc/XJgsJAoQ9r+e1qlcNR41UYmX8WbfiTRJ87Os+iK1GmNRnZD+PUZtZgaFC 6qOvqyDSp1wAPJ6fNPgSqemTAOQ930QntEASxIwgYsFbzKvfXZfUHKc+5+gYRmfXQyj2j9g1W lupSLnWg2y86QOmLS4Zf9t1Ha86AuGBVKtqXeNo40na4C9TpOaofiyMQxQJ8In4XeoHPrdPkR KJdVISgxCNdoZv8YgWR31Vf6ScOQQdHxMJ9dAqpPOG2xPfd03ouiZe3GQkxLzdBgSVANsEjhT lik1PwM02FHO0tcoCfn+vhcFyZzUCeAp9Z98ev/4tM2c+UdIm+1hwQ2A35zX4p7WcF2lPG9Cf 1lTpoV6hKQYXj0Oekx2YAbYlyq0Q6GFqyuiAzbUNeTFOP5PgXwhr1uNQDQioRNv+a2COIQb6T tJFw8/p Cc: cake@lists.bufferbloat.net Subject: Re: [Cake] Long-RTT broken again 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 11:08:43 -0000 Hi Kevin, On Nov 3, 2015, at 11:29 , Kevin Darbyshire-Bryant = wrote: >=20 >=20 > On 03/11/15 08:34, Sebastian Moeller wrote: >=20 >> Hi Jonathan, >>=20 >> On Nov 3, 2015, at 09:25 , Jonathan Morton = wrote: >>=20 >>>> On 3 Nov, 2015, at 10:20, Sebastian Moeller = wrote: >>>>=20 >>>> Also what about the BUG_ON I managed to trigger during my testing? >>> That turned out to be a flawed condition, which I=92ve already = fixed. >>=20 > If my git-blame-fu is working right this morning, then Dave is the one > who with the aid of commit c4f75d38 turned "BUG_ON(CAKE_MAX_BINS < > q->bin_cnt);" into "BUG_ON(q->bin_cnt >=3D CAKE_MAX_BINS);" and = introduced > a classic 'off-by-one/fencepost' error on 2015-10-05. A reconfigure > using 'diffserv8' should have blown up quite nicely after that date = and > suggests little testing has been done with diffserv8 since that time. >=20 > Well done Seb for clearly treading rarely visited areas of the code! Fair enough so the initial BUG_ON seems to have been safe. >=20 > BUG_ON I put in the category of "Never test for a condition you don't > know how to handle" ;-) Now that the off-by-one has been stomped on = I'm > going to stick my neck out and say that bin_cnt > 8 implies something > has stomped on our config structure and we really shouldn't be = trusting > anything in it. Goodness knows what our skb queues are like...and = err, > help! Also note that the correctly written BUG_ON didn't explode for > many months. Well, not my call, but I have seen discussions on LKML about = this topic with the general gist that a BUG_ON needs to be justified, = and only be there is the situation is not salvageable. After all we take = down a whole machine that might be doing something really really = important... >=20 > I'm happy with it being there. As long as it can never trigger I guess I do not care too much = about this either. But the fact that we managed to get it wrong does not = fill me with confidence (I seem to suffer from a lack of confidence = lately...) Best Regards Sebastian >=20 > _______________________________________________ > Cake mailing list > Cake@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/cake