- struct red_sched_data *q = qdisc_priv(sch);
-
- psched_time_t now;
-
- if (!PSCHED_IS_PASTPERFECT(q->qidlestart)) {
- long us_idle;
- int shift;
-
- PSCHED_GET_TIME(now);
- us_idle = PSCHED_TDIFF_SAFE(now, q->qidlestart, q->Scell_max);
- PSCHED_SET_PASTPERFECT(q->qidlestart);
-
-/*
- The problem: ideally, average length queue recalcultion should
- be done over constant clock intervals. This is too expensive, so that
- the calculation is driven by outgoing packets.
- When the queue is idle we have to model this clock by hand.
-
- SF+VJ proposed to "generate" m = idletime/(average_pkt_size/bandwidth)
- dummy packets as a burst after idle time, i.e.
-
- q->qave *= (1-W)^m
-
- This is an apparently overcomplicated solution (f.e. we have to precompute
- a table to make this calculation in reasonable time)
- I believe that a simpler model may be used here,
- but it is field for experiments.
-*/
- shift = q->Stab[us_idle>>q->Scell_log];
-
- if (shift) {
- q->qave >>= shift;
- } else {
- /* Approximate initial part of exponent
- with linear function:
- (1-W)^m ~= 1-mW + ...
-
- Seems, it is the best solution to
- problem of too coarce exponent tabulation.
- */
-
- us_idle = (q->qave * us_idle)>>q->Scell_log;
- if (us_idle < q->qave/2)
- q->qave -= us_idle;
- else
- q->qave >>= 1;
- }
- } else {
- q->qave += sch->stats.backlog - (q->qave >> q->Wlog);
- /* NOTE:
- q->qave is fixed point number with point at Wlog.
- The formulae above is equvalent to floating point
- version:
-
- qave = qave*(1-W) + sch->stats.backlog*W;
- --ANK (980924)
- */
- }