[PKT_SCHED]: RED: Use new generic red interface
Thomas Graf [Sat, 5 Nov 2005 20:14:05 +0000 (21:14 +0100)]
Simplifies code a lot by separating the red algorithm and the
queueing logic. We now differentiate between probability marks
and forced marks but sum them together again to not break
backwards compatibility.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>

net/sched/sch_red.c

index 7845d04..0dabcc9 100644 (file)
 #include <net/pkt_sched.h>
 #include <net/inet_ecn.h>
 #include <net/dsfield.h>
+#include <net/red.h>
 
 
-/*     Random Early Detection (RED) algorithm.
-       =======================================
-
-       Source: Sally Floyd and Van Jacobson, "Random Early Detection Gateways
-       for Congestion Avoidance", 1993, IEEE/ACM Transactions on Networking.
-
-       This file codes a "divisionless" version of RED algorithm
-       as written down in Fig.17 of the paper.
-
-Short description.
-------------------
-
-       When a new packet arrives we calculate the average queue length:
-
-       avg = (1-W)*avg + W*current_queue_len,
-
-       W is the filter time constant (chosen as 2^(-Wlog)), it controls
-       the inertia of the algorithm. To allow larger bursts, W should be
-       decreased.
-
-       if (avg > th_max) -> packet marked (dropped).
-       if (avg < th_min) -> packet passes.
-       if (th_min < avg < th_max) we calculate probability:
-
-       Pb = max_P * (avg - th_min)/(th_max-th_min)
-
-       and mark (drop) packet with this probability.
-       Pb changes from 0 (at avg==th_min) to max_P (avg==th_max).
-       max_P should be small (not 1), usually 0.01..0.02 is good value.
-
-       max_P is chosen as a number, so that max_P/(th_max-th_min)
-       is a negative power of two in order arithmetics to contain
-       only shifts.
-
-
-       Parameters, settable by user:
+/*     Parameters, settable by user:
        -----------------------------
 
        limit           - bytes (must be > qth_max + burst)
@@ -89,92 +55,19 @@ Short description.
        arbitrarily high (well, less than ram size)
        Really, this limit will never be reached
        if RED works correctly.
-
-       qth_min         - bytes (should be < qth_max/2)
-       qth_max         - bytes (should be at least 2*qth_min and less limit)
-       Wlog            - bits (<32) log(1/W).
-       Plog            - bits (<32)
-
-       Plog is related to max_P by formula:
-
-       max_P = (qth_max-qth_min)/2^Plog;
-
-       F.e. if qth_max=128K and qth_min=32K, then Plog=22
-       corresponds to max_P=0.02
-
-       Scell_log
-       Stab
-
-       Lookup table for log((1-W)^(t/t_ave).
-
-
-NOTES:
-
-Upper bound on W.
------------------
-
-       If you want to allow bursts of L packets of size S,
-       you should choose W:
-
-       L + 1 - th_min/S < (1-(1-W)^L)/W
-
-       th_min/S = 32         th_min/S = 4
-                                              
-       log(W)  L
-       -1      33
-       -2      35
-       -3      39
-       -4      46
-       -5      57
-       -6      75
-       -7      101
-       -8      135
-       -9      190
-       etc.
  */
 
 struct red_sched_data
 {
-/* Parameters */
-       u32             limit;          /* HARD maximal queue length    */
-       u32             qth_min;        /* Min average length threshold: A scaled */
-       u32             qth_max;        /* Max average length threshold: A scaled */
-       u32             Rmask;
-       u32             Scell_max;
-       unsigned char   flags;
-       char            Wlog;           /* log(W)               */
-       char            Plog;           /* random number bits   */
-       char            Scell_log;
-       u8              Stab[256];
-
-/* Variables */
-       unsigned long   qave;           /* Average queue length: A scaled */
-       int             qcount;         /* Packets since last random number generation */
-       u32             qR;             /* Cached random number */
-
-       psched_time_t   qidlestart;     /* Start of idle period         */
-       struct tc_red_xstats st;
+       u32                     limit;          /* HARD maximal queue length */
+       unsigned char           flags;
+       struct red_parms        parms;
+       struct red_stats        stats;
 };
 
-static int red_ecn_mark(struct sk_buff *skb)
+static inline int red_use_ecn(struct red_sched_data *q)
 {
-       if (skb->nh.raw + 20 > skb->tail)
-               return 0;
-
-       switch (skb->protocol) {
-       case __constant_htons(ETH_P_IP):
-               if (INET_ECN_is_not_ect(skb->nh.iph->tos))
-                       return 0;
-               IP_ECN_set_ce(skb->nh.iph);
-               return 1;
-       case __constant_htons(ETH_P_IPV6):
-               if (INET_ECN_is_not_ect(ipv6_get_dsfield(skb->nh.ipv6h)))
-                       return 0;
-               IP6_ECN_set_ce(skb->nh.ipv6h);
-               return 1;
-       default:
-               return 0;
-       }
+       return q->flags & TC_RED_ECN;
 }
 
 static int
@@ -182,119 +75,50 @@ red_enqueue(struct sk_buff *skb, struct Qdisc* sch)
 {
        struct red_sched_data *q = qdisc_priv(sch);
 
-       psched_time_t now;
+       q->parms.qavg = red_calc_qavg(&q->parms, sch->qstats.backlog);
 
-       if (!PSCHED_IS_PASTPERFECT(q->qidlestart)) {
-               long us_idle;
-               int  shift;
+       if (red_is_idling(&q->parms))
+               red_end_of_idle_period(&q->parms);
 
-               PSCHED_GET_TIME(now);
-               us_idle = PSCHED_TDIFF_SAFE(now, q->qidlestart, q->Scell_max);
-               PSCHED_SET_PASTPERFECT(q->qidlestart);
+       switch (red_action(&q->parms, q->parms.qavg)) {
+               case RED_DONT_MARK:
+                       break;
 
-/*
-   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->qstats.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->qstats.backlog*W;
-                                                          --ANK (980924)
-                */
-       }
+               case RED_PROB_MARK:
+                       sch->qstats.overlimits++;
+                       if (!red_use_ecn(q) || !INET_ECN_set_ce(skb)) {
+                               q->stats.prob_drop++;
+                               goto congestion_drop;
+                       }
 
-       if (q->qave < q->qth_min) {
-               q->qcount = -1;
-enqueue:
-               if (sch->qstats.backlog + skb->len <= q->limit) {
-                       __skb_queue_tail(&sch->q, skb);
-                       sch->qstats.backlog += skb->len;
-                       sch->bstats.bytes += skb->len;
-                       sch->bstats.packets++;
-                       return NET_XMIT_SUCCESS;
-               } else {
-                       q->st.pdrop++;
-               }
-               kfree_skb(skb);
-               sch->qstats.drops++;
-               return NET_XMIT_DROP;
-       }
-       if (q->qave >= q->qth_max) {
-               q->qcount = -1;
-               sch->qstats.overlimits++;
-mark:
-               if  (!(q->flags&TC_RED_ECN) || !red_ecn_mark(skb)) {
-                       q->st.early++;
-                       goto drop;
-               }
-               q->st.marked++;
-               goto enqueue;
+                       q->stats.prob_mark++;
+                       break;
+
+               case RED_HARD_MARK:
+                       sch->qstats.overlimits++;
+                       if (!red_use_ecn(q) || !INET_ECN_set_ce(skb)) {
+                               q->stats.forced_drop++;
+                               goto congestion_drop;
+                       }
+
+                       q->stats.forced_mark++;
+                       break;
        }
 
-       if (++q->qcount) {
-               /* The formula used below causes questions.
-
-                  OK. qR is random number in the interval 0..Rmask
-                  i.e. 0..(2^Plog). If we used floating point
-                  arithmetics, it would be: (2^Plog)*rnd_num,
-                  where rnd_num is less 1.
-
-                  Taking into account, that qave have fixed
-                  point at Wlog, and Plog is related to max_P by
-                  max_P = (qth_max-qth_min)/2^Plog; two lines
-                  below have the following floating point equivalent:
-                  
-                  max_P*(qave - qth_min)/(qth_max-qth_min) < rnd/qcount
-
-                  Any questions? --ANK (980924)
-                */
-               if (((q->qave - q->qth_min)>>q->Wlog)*q->qcount < q->qR)
-                       goto enqueue;
-               q->qcount = 0;
-               q->qR = net_random()&q->Rmask;
-               sch->qstats.overlimits++;
-               goto mark;
+       if (sch->qstats.backlog + skb->len <= q->limit) {
+               __skb_queue_tail(&sch->q, skb);
+               sch->qstats.backlog += skb->len;
+               sch->bstats.bytes += skb->len;
+               sch->bstats.packets++;
+               return NET_XMIT_SUCCESS;
        }
-       q->qR = net_random()&q->Rmask;
-       goto enqueue;
 
-drop:
+       q->stats.pdrop++;
+       kfree_skb(skb);
+       sch->qstats.drops++;
+       return NET_XMIT_DROP;
+
+congestion_drop:
        kfree_skb(skb);
        sch->qstats.drops++;
        return NET_XMIT_CN;
@@ -305,7 +129,8 @@ red_requeue(struct sk_buff *skb, struct Qdisc* sch)
 {
        struct red_sched_data *q = qdisc_priv(sch);
 
-       PSCHED_SET_PASTPERFECT(q->qidlestart);
+       if (red_is_idling(&q->parms))
+               red_end_of_idle_period(&q->parms);
 
        __skb_queue_head(&sch->q, skb);
        sch->qstats.backlog += skb->len;
@@ -324,7 +149,8 @@ red_dequeue(struct Qdisc* sch)
                sch->qstats.backlog -= skb->len;
                return skb;
        }
-       PSCHED_GET_TIME(q->qidlestart);
+
+       red_start_of_idle_period(&q->parms);
        return NULL;
 }
 
@@ -338,11 +164,12 @@ static unsigned int red_drop(struct Qdisc* sch)
                unsigned int len = skb->len;
                sch->qstats.backlog -= len;
                sch->qstats.drops++;
-               q->st.other++;
+               q->stats.other++;
                kfree_skb(skb);
                return len;
        }
-       PSCHED_GET_TIME(q->qidlestart);
+
+       red_start_of_idle_period(&q->parms);
        return 0;
 }
 
@@ -352,9 +179,7 @@ static void red_reset(struct Qdisc* sch)
 
        __skb_queue_purge(&sch->q);
        sch->qstats.backlog = 0;
-       PSCHED_SET_PASTPERFECT(q->qidlestart);
-       q->qave = 0;
-       q->qcount = -1;
+       red_restart(&q->parms);
 }
 
 static int red_change(struct Qdisc *sch, struct rtattr *opt)
@@ -374,19 +199,14 @@ static int red_change(struct Qdisc *sch, struct rtattr *opt)
 
        sch_tree_lock(sch);
        q->flags = ctl->flags;
-       q->Wlog = ctl->Wlog;
-       q->Plog = ctl->Plog;
-       q->Rmask = ctl->Plog < 32 ? ((1<<ctl->Plog) - 1) : ~0UL;
-       q->Scell_log = ctl->Scell_log;
-       q->Scell_max = (255<<q->Scell_log);
-       q->qth_min = ctl->qth_min<<ctl->Wlog;
-       q->qth_max = ctl->qth_max<<ctl->Wlog;
        q->limit = ctl->limit;
-       memcpy(q->Stab, RTA_DATA(tb[TCA_RED_STAB-1]), 256);
 
-       q->qcount = -1;
+       red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
+                                ctl->Plog, ctl->Scell_log,
+                                RTA_DATA(tb[TCA_RED_STAB-1]));
+
        if (skb_queue_empty(&sch->q))
-               PSCHED_SET_PASTPERFECT(q->qidlestart);
+               red_end_of_idle_period(&q->parms);
        sch_tree_unlock(sch);
        return 0;
 }
@@ -401,17 +221,18 @@ static int red_dump(struct Qdisc *sch, struct sk_buff *skb)
        struct red_sched_data *q = qdisc_priv(sch);
        unsigned char    *b = skb->tail;
        struct rtattr *rta;
-       struct tc_red_qopt opt;
+       struct tc_red_qopt opt = {
+               .limit          = q->limit,
+               .flags          = q->flags,
+               .qth_min        = q->parms.qth_min >> q->parms.Wlog,
+               .qth_max        = q->parms.qth_max >> q->parms.Wlog,
+               .Wlog           = q->parms.Wlog,
+               .Plog           = q->parms.Plog,
+               .Scell_log      = q->parms.Scell_log,
+       };
 
        rta = (struct rtattr*)b;
        RTA_PUT(skb, TCA_OPTIONS, 0, NULL);
-       opt.limit = q->limit;
-       opt.qth_min = q->qth_min>>q->Wlog;
-       opt.qth_max = q->qth_max>>q->Wlog;
-       opt.Wlog = q->Wlog;
-       opt.Plog = q->Plog;
-       opt.Scell_log = q->Scell_log;
-       opt.flags = q->flags;
        RTA_PUT(skb, TCA_RED_PARMS, sizeof(opt), &opt);
        rta->rta_len = skb->tail - b;
 
@@ -425,8 +246,14 @@ rtattr_failure:
 static int red_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 {
        struct red_sched_data *q = qdisc_priv(sch);
-
-       return gnet_stats_copy_app(d, &q->st, sizeof(q->st));
+       struct tc_red_xstats st = {
+               .early  = q->stats.prob_drop + q->stats.forced_drop,
+               .pdrop  = q->stats.pdrop,
+               .other  = q->stats.other,
+               .marked = q->stats.prob_mark + q->stats.forced_mark,
+       };
+
+       return gnet_stats_copy_app(d, &st, sizeof(st));
 }
 
 static struct Qdisc_ops red_qdisc_ops = {