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Date: Fri, 14 Jan 2011 04:29:53 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: Stephen Hemminger <shemminger@...tta.com>
Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] CHOKe flow scheduler (0.8)
Le jeudi 13 janvier 2011 à 15:34 -0800, Stephen Hemminger a écrit :
> CHOKe ("CHOose and Kill" or "CHOose and Keep") is an alternative
> packet scheduler based on the Random Exponential Drop (RED) algorithm.
>
> The core idea is:
> For every packet arrival:
> Calculate Qave
> if (Qave < minth)
> Queue the new packet
> else
> Select randomly a packet from the queue
> if (both packets from same flow)
> then Drop both the packets
> else if (Qave > maxth)
> Drop packet
> else
> Admit packet with probability P (same as RED)
>
> See also:
> Rong Pan, Balaji Prabhakar, Konstantinos Psounis, "CHOKe: a stateless active
> queue management scheme for approximating fair bandwidth allocation",
> Proceeding of INFOCOM'2000, March 2000.
>
> Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
>
> ---
> 0.8 change queue length and holes account.
> keep sch->q.qlen updated, and holes counter not needed.
>
> ---
> net/sched/Kconfig | 11 +
> net/sched/Makefile | 1
> net/sched/sch_choke.c | 536 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 548 insertions(+)
>
Hi Stephen
Your diffstat was an old one, here the right one.
include/linux/pkt_sched.h | 29 +
net/sched/Kconfig | 11
net/sched/Makefile | 1
net/sched/sch_choke.c | 552 ++++++++++++++++++++++++++++++++++++
I tested v8 and found several serious problems, please find a diff of my
latest changes :
- wrong oskb/skb used in choke_enqueue()
- choke_zap_head_holes() is called from choke_dequeue() and crash if we
dequeued last packet. (!!!)
- out of bound access in choke_zap_tail_holes()
- choke_dequeue() can be shorter
- choke_change() must dequeue/drop in excess packets or risk new array
overfill (if we reduce queue limit by tc qdisc change ...)
- inline is not needed, space errors in include file
Thanks !
include/linux/pkt_sched.h | 8 +++---
net/sched/sch_choke.c | 43 ++++++++++++++++++++++--------------
2 files changed, 31 insertions(+), 20 deletions(-)
diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
index 83bac92..498c798 100644
--- a/include/linux/pkt_sched.h
+++ b/include/linux/pkt_sched.h
@@ -269,10 +269,10 @@ struct tc_choke_qopt {
};
struct tc_choke_xstats {
- __u32 early; /* Early drops */
- __u32 pdrop; /* Drops due to queue limits */
- __u32 other; /* Drops due to drop() calls */
- __u32 marked; /* Marked packets */
+ __u32 early; /* Early drops */
+ __u32 pdrop; /* Drops due to queue limits */
+ __u32 other; /* Drops due to drop() calls */
+ __u32 marked; /* Marked packets */
__u32 matched; /* Drops due to flow match */
};
diff --git a/net/sched/sch_choke.c b/net/sched/sch_choke.c
index 136d4e5..c710c57 100644
--- a/net/sched/sch_choke.c
+++ b/net/sched/sch_choke.c
@@ -74,7 +74,7 @@ struct choke_sched_data {
};
/* deliver a random number between 0 and N - 1 */
-static inline u32 random_N(unsigned int N)
+static u32 random_N(unsigned int N)
{
return reciprocal_divide(random32(), N);
}
@@ -99,13 +99,13 @@ static struct sk_buff *choke_peek_random(struct Qdisc *sch,
}
/* Is ECN parameter configured */
-static inline int use_ecn(const struct choke_sched_data *q)
+static int use_ecn(const struct choke_sched_data *q)
{
return q->flags & TC_RED_ECN;
}
/* Should packets over max just be dropped (versus marked) */
-static inline int use_harddrop(const struct choke_sched_data *q)
+static int use_harddrop(const struct choke_sched_data *q)
{
return q->flags & TC_RED_HARDDROP;
}
@@ -113,20 +113,21 @@ static inline int use_harddrop(const struct choke_sched_data *q)
/* Move head pointer forward to skip over holes */
static void choke_zap_head_holes(struct choke_sched_data *q)
{
- while (q->tab[q->head] == NULL) {
+ do {
q->head = (q->head + 1) & q->tab_mask;
-
- BUG_ON(q->head == q->tail);
- }
+ if (q->head == q->tail)
+ break;
+ } while (q->tab[q->head] == NULL);
}
/* Move tail pointer backwards to reuse holes */
static void choke_zap_tail_holes(struct choke_sched_data *q)
{
- while (q->tab[q->tail - 1] == NULL) {
+ do {
q->tail = (q->tail - 1) & q->tab_mask;
- BUG_ON(q->head == q->tail);
- }
+ if (q->head == q->tail)
+ break;
+ } while (q->tab[q->tail] == NULL);
}
/* Drop packet from queue array by creating a "hole" */
@@ -145,7 +146,7 @@ static void choke_drop_by_idx(struct choke_sched_data *q, unsigned int idx)
2. fast internal classification
3. use TC filter based classification
*/
-static inline unsigned int choke_classify(struct sk_buff *skb,
+static unsigned int choke_classify(struct sk_buff *skb,
struct Qdisc *sch, int *qerr)
{
@@ -218,7 +219,7 @@ static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch)
/* Drop both packets */
q->stats.matched++;
choke_drop_by_idx(q, idx);
- sch->qstats.backlog -= qdisc_pkt_len(skb);
+ sch->qstats.backlog -= qdisc_pkt_len(oskb);
--sch->q.qlen;
qdisc_drop(oskb, sch);
goto congestion_drop;
@@ -285,8 +286,7 @@ static struct sk_buff *choke_dequeue(struct Qdisc *sch)
}
skb = q->tab[q->head];
- q->tab[q->head] = NULL; /* not really needed */
- q->head = (q->head + 1) & q->tab_mask;
+ q->tab[q->head] = NULL;
choke_zap_head_holes(q);
--sch->q.qlen;
sch->qstats.backlog -= qdisc_pkt_len(skb);
@@ -371,12 +371,23 @@ static int choke_change(struct Qdisc *sch, struct nlattr *opt)
sch_tree_lock(sch);
old = q->tab;
if (old) {
- unsigned int tail = 0;
+ unsigned int oqlen = sch->q.qlen, tail = 0;
while (q->head != q->tail) {
- ntab[tail++] = q->tab[q->head];
+ struct sk_buff *skb = q->tab[q->head];
+
q->head = (q->head + 1) & q->tab_mask;
+ if (!skb)
+ continue;
+ if (tail < mask) {
+ ntab[tail++] = skb;
+ continue;
+ }
+ sch->qstats.backlog -= qdisc_pkt_len(skb);
+ --sch->q.qlen;
+ qdisc_drop(skb, sch);
}
+ qdisc_tree_decrease_qlen(sch, oqlen - sch->q.qlen);
q->head = 0;
q->tail = tail;
}
--
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