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[PKT_SCHED]: RED: Use new generic red interface

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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>
This commit is contained in:
Thomas Graf 2005-11-05 21:14:05 +01:00 committed by Thomas Graf
parent 2566a509ca
commit 6b31b28a44
1 changed files with 70 additions and 243 deletions
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313
net/sched/sch_red.c
View File

@ -41,44 +41,10 @@
#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.
case RED_PROB_MARK:
sch->qstats.overlimits++;
if (!red_use_ecn(q) || !INET_ECN_set_ce(skb)) {
q->stats.prob_drop++;
goto congestion_drop;
}
SF+VJ proposed to "generate" m = idletime/(average_pkt_size/bandwidth)
dummy packets as a burst after idle time, i.e.
q->stats.prob_mark++;
break;
q->qave *= (1-W)^m
case RED_HARD_MARK:
sch->qstats.overlimits++;
if (!red_use_ecn(q) || !INET_ECN_set_ce(skb)) {
q->stats.forced_drop++;
goto congestion_drop;
}
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)
*/
q->stats.forced_mark++;
break;
}
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;
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;
}
if (++q->qcount) {
/* The formula used below causes questions.
q->stats.pdrop++;
kfree_skb(skb);
sch->qstats.drops++;
return NET_XMIT_DROP;
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;
}
q->qR = net_random()&q->Rmask;
goto enqueue;
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);
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, &q->st, sizeof(q->st));
return gnet_stats_copy_app(d, &st, sizeof(st));
}
static struct Qdisc_ops red_qdisc_ops = {