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 :)
