Hi Nogah! On Mon, 28 May 2018 18:49:51 +0300, Nogah Frankel wrote: > > +static int > > +nfp_abm_red_replace(struct net_device *netdev, struct nfp_abm_link *alink, > > + struct tc_red_qopt_offload *opt) > > +{ > > + struct nfp_port *port = nfp_port_from_netdev(netdev); > > + int err; > > + > > + if (opt->set.min != opt->set.max || !opt->set.is_ecn) { > > I am a bit worried about the min == max. > sch_red doesn't really support it. It will calculate incorrect delta > value. (And that only if tc_red_eval_P in iproute2 won't reject it). > You might maybe use max = min+1, because in real life it will probably > act the same but without this problem.
I remember having a long think about this when I wrote the code. My conclusion was that the two would operate almost the same, and setting min == max may be most obvious to the user. If min + 1 == max sch_red would act probabilistically for qavg == min, which is not what the card would do. Userspace now does this: tc_red_eval_P() { int i = qmax - qmin; if (!i) return 0; if (i < 0) return -1; ... } And you've fixed delta to be treated as 1 to avoid division by 0 in commit 5c472203421a ("net_sched: red: Avoid devision by zero"): red_set_parms() { int delta = qth_max - qth_min; u32 max_p_delta; p->qth_min = qth_min << Wlog; p->qth_max = qth_max << Wlog; p->Wlog = Wlog; p->Plog = Plog; if (delta <= 0) delta = 1; p->qth_delta = delta; ... } So we should be safe. Targets will match. Probability adjustment for adaptive should work correctly. Which doesn't matter anyway, since we will never use the probabilistic action... > Nogah Frankel > (from a new mail address) Noted :)