> On Jan 5, 2019, at 2:35 PM, Toke Høiland-Jørgensen <[email protected]> wrote: > > Pete Heist <[email protected]> writes: > >>> On Jan 5, 2019, at 2:10 PM, Toke Høiland-Jørgensen <[email protected]> wrote: >>> >>> Hmm, that's odd. Could you try adding this debugging line in >>> adjust_parent_qlen(), right before the sch->q.qlen += n line: >>> >>> net_info_ratelimited("Adjusting parent qdisc %d with pkt += %d, >>> len += %d", >>> parentid, n, len); >>> >>> And see if you actually get any of those lines in your dmesg? >> >> I do see the messages twice, then not after that in the rest of the >> output... > > Right. Looking at the HFSC code some more, I think the bug is actually > caused by another, but related, interaction between HFSC and CAKE. > > Specifically, this line: > > https://elixir.bootlin.com/linux/v3.16.7/source/net/sched/sch_hfsc.c#L1605 > > 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). > > 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’ll 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’s nobody in MAINTAINERS for hfsc, so we may not get much of a response to any bug submissions... Pete _______________________________________________ Cake mailing list [email protected] https://lists.bufferbloat.net/listinfo/cake
