Eric Dumazet <eric.duma...@gmail.com> wrote: > On Wed, 2016-06-01 at 01:00 +0200, Florian Westphal wrote: > Generally speaking, a non work conserving qdisc could return NULL if it > decides to drop all packet(s) that were sitting in the queue. > > Say we add a 'max sojourn time' on skbs, as yet another anti-bloat > features, in a Codel variant/extension. > > HFSC does check this and eventually complains ( qdisc_warn_nonwc()), > but all its precise computations are probably wrong.
Right, this is already a problem when using hfsc with silly fq_codel config (we can end up with underflow on sch->q.qlen, i.e. hfsc ends up thinking it has 0xffffffff packets in class while fq_codel has 0). > > > If you want to make HFSC generic, you would need a lot more changes. > > > > Could you elaborate? > > HFSC is based on packet lengths and realtime/deadline constraints. > > With lazy packet lengths (if the attached children qdisc reorder > packets), this all becomes fuzzy. Which might be OK or not. > > We are not helping users by silently making such decisions. > Maybe they prefer to be warned so that they can fix their setup. Seems that limits us to pfifo or prio+pfifo only... > > I'm not interested in e.g. tbf leaves (makes no sense to me), but I > > think it should play nice with netem, sfq, codel, fq_codel, fq, ... > > > > I don't see any problems with fq_codel + hfsc unless I deliberately > > misconfigure fq_codel (setting extremely low mem limit, e.g. 32kbyte). > > That is pure luck, then. I would not be surprised that HTB + nonwc qdisc > would actually crash in some cases. Ugh. I think that using codel, sfq, fq_codel etc. should just work when used with htb or hfsc. Using tbf and friends should at least not crash kernel (it would be nice if we could complain and/or reject at config time though). Thanks for your input, I see this isn't easy to resolve.
