[LARTC] Re: further CBQ/tc documentation ds9a.nl/lartc/manpages

[bert hubert <ahu@ds9a.nl>]

On Sat, Dec 08, 2001 at 06:30:47PM -0500, jamal wrote:
> 
> 
> On Sun, 9 Dec 2001, bert hubert wrote:
> 
> >
> > I will, but I bet you 5 euros that I'm right :-) We are talking about the
> > TBF, aren't we?
> >
> 
> The trick is that TBF delays packets and the policer drops packet when
> exceeding their profile.

Well, we're both right to some extent. The policer drops packets which are
larger than the configured MTU, but it also dimensions the second bucket to
be of size mtu! 

From net/sched/police.c (trimmed a bit, added some comments):
int tcf_police(struct sk_buff *skb, struct tcf_police *p)
{
        psched_time_t now;
        long toks,ptoks = 0;

        spin_lock(&p->lock);

        p->stats.bytes += skb->len;
        p->stats.packets++;

        if (skb->len <= p->mtu) {
                if (p->R_tab = NULL) {
                        spin_unlock(&p->lock);
                        return p->result;
                }

                PSCHED_GET_TIME(now);

                toks = PSCHED_TDIFF_SAFE(now, p->t_c, p->burst, 0);
		// tokens that arrived since last invocation

                if (p->P_tab) {
                        ptoks = toks + p->ptoks;
                        if (ptoks > (long)L2T_P(p, p->mtu))
                                ptoks = (long)L2T_P(p, p->mtu); 
			// cap total available ptokens to mtu
                        ptoks -= L2T_P(p, skb->len);
                        // deduct packet size
                }
                toks += p->toks; 
                if (toks > (long)p->burst)
                        toks = p->burst;
                // cap regular number of tokens

                toks -= L2T(p, skb->len);
                // deduct packet size

                if ((toks|ptoks) >= 0) { // send if both are positive
                        p->t_c = now;
                        p->toks = toks;  // do accounting
                        p->ptoks = ptoks;
                        spin_unlock(&p->lock);
                        return p->result;
                }
        }

        p->stats.overlimits++;
        spin_unlock(&p->lock);
        return p->action;
}

It's a draw? :-)

Regards,

bert

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