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[185.193.85.130]) by smtp.gmail.com with ESMTPSA id o9sm2787093wmh.3.2019.01.05.07.34.25 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 05 Jan 2019 07:34:26 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) From: Pete Heist In-Reply-To: <87o98vxm57.fsf@toke.dk> Date: Sat, 5 Jan 2019 16:34:24 +0100 Cc: Cake List Content-Transfer-Encoding: quoted-printable Message-Id: <797FCC60-0048-4EF6-80BC-19707E9173FB@heistp.net> References: <5482A3CA-9C36-4DDE-A858-24D8467F70C7@heistp.net> <8736q8yumt.fsf@toke.dk> <4C422792-7E51-4DBA-A229-FA7D3F987FB6@heistp.net> <87zhsgxdao.fsf@toke.dk> <87wonjxvss.fsf@toke.dk> <0077CC34-490F-4D76-82D3-BE37B27F2E1C@heistp.net> <49A6DCF8-BE98-47F4-9C66-6B4288390A58@heistp.net> <87tvinxos7.fsf@toke.dk> <87r2drxnal.fsf@toke.dk> <45D43135-318B-48AD-B09B-69BBB034CE12@heistp.net> <87o98vxm57.fsf@toke.dk> To: =?utf-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= X-Mailer: Apple Mail (2.3445.9.1) Subject: Re: [Cake] cake infinite loop(?) with hfsc on one-armed router 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: Sat, 05 Jan 2019 15:34:28 -0000 > On Jan 5, 2019, at 2:35 PM, Toke H=C3=B8iland-J=C3=B8rgensen = wrote: >=20 > Pete Heist writes: >=20 >>> On Jan 5, 2019, at 2:10 PM, Toke H=C3=B8iland-J=C3=B8rgensen = wrote: >>>=20 >>> Hmm, that's odd. Could you try adding this debugging line in >>> adjust_parent_qlen(), right before the sch->q.qlen +=3D n line: >>>=20 >>> net_info_ratelimited("Adjusting parent qdisc %d with pkt = +=3D %d, len +=3D %d", >>> parentid, n, len); >>>=20 >>> And see if you actually get any of those lines in your dmesg? >>=20 >> I do see the messages twice, then not after that in the rest of the >> output... >=20 > Right. Looking at the HFSC code some more, I think the bug is actually > caused by another, but related, interaction between HFSC and CAKE. >=20 > Specifically, this line: >=20 > = https://elixir.bootlin.com/linux/v3.16.7/source/net/sched/sch_hfsc.c#L1605= >=20 > where HFSC checks whether the child queue len is 1, which it = interprets > as the event that activates that queue. However, because CAKE splits = the > packet, this check will fail, and the HFSC class will not be = activated. > This also explains why you only see the bug with HFSC, and not with = HTB > (although I do think that we still need to update the hierarchy). >=20 > The good news it that it is a fairly simple to fix in HFSC. The bad = news > is that it's something that's hard to work around from the out-of-tree > CAKE... Aha, well, I wonder if we=E2=80=99ll see this problem with other qdiscs- = maybe cbq, if I ever get a chance to try it (not hurrying yet). Ideally = this interaction between qdiscs would be clarified somewhere, at some = point. :) Thanks a lot for doing the discovery though! We may not have hfsc+cake = with GSO splitting on older kernels very soon, but what should we do = with this? There=E2=80=99s nobody in MAINTAINERS for hfsc, so we may not = get much of a response to any bug submissions... Pete