From: Eric Dumazet <eric.dumazet@gmail.com>
To: Jonathan Morton <chromatix99@gmail.com>
Cc: bloat@lists.bufferbloat.net
Subject: Re: [Bloat] Thoughts on Stochastic Fair Blue
Date: Thu, 24 Mar 2011 14:32:36 +0100 [thread overview]
Message-ID: <1300973556.3747.9.camel@edumazet-laptop> (raw)
In-Reply-To: <160809C8-284C-4463-97FE-0E2F03C08589@gmail.com>
Le jeudi 24 mars 2011 à 14:40 +0200, Jonathan Morton a écrit :
> Finally, it might also be interesting and useful to add bare-bones ECN
> support to the existing "dumb" qdiscs, such as SFQ and the FIFO
> family. Simply start marking (and dropping non-supporting flows) when
> the queue is more than half full.
Three months ago, I played with a SFQ patch to add ECN support, based on
delay of packet in queue.
http://www.spinics.net/lists/netdev/msg151594.html
This patch is a hack of course (units are jiffies ticks, not ms)
--------------------------------------
Here is the POC patch I am currently testing, with a probability to
"early drop" a packet of one percent per ms (HZ=1000 here), only if
packet stayed at least 4 ms on queue.
Of course, this only apply where SFQ is used, with known SFQ limits :)
The term "early drop" is a lie. RED really early mark/drop a packet at
enqueue() time, while I do it at dequeue() time [since I need to compute
the delay]. But effect is the same on sent packets. This might use a bit
more memory, but no more than current SFQ [and only if flows dont react
to mark/drops]
insmod net/sched/sch_sfq.ko red_delay=4
By the way, I do think we should lower SFQ_DEPTH a bit and increase
SFQ_SLOTS by same amount. Allowing 127 packets per flow seems not
necessary in most situations SFQ might be used.
net/sched/sch_sfq.c | 37 +++++++++++++++++++++++++++++++++----
1 files changed, 33 insertions(+), 4 deletions(-)
diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index d54ac94..4f958e3 100644
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -24,6 +24,8 @@
#include <net/ip.h>
#include <net/netlink.h>
#include <net/pkt_sched.h>
+#include <net/inet_ecn.h>
+#include <linux/moduleparam.h>
/* Stochastic Fairness Queuing algorithm.
@@ -86,6 +88,10 @@
/* This type should contain at least SFQ_DEPTH + SFQ_SLOTS values */
typedef unsigned char sfq_index;
+static int red_delay; /* default : no RED handling */
+module_param(red_delay, int, 0);
+MODULE_PARM_DESC(red_delay, "mark/drop packets if they stay in queue longer than red_delay ticks");
+
/*
* We dont use pointers to save space.
* Small indexes [0 ... SFQ_SLOTS - 1] are 'pointers' to slots[] array
@@ -391,6 +397,7 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
sch->qstats.backlog += qdisc_pkt_len(skb);
slot_queue_add(slot, skb);
+ qdisc_skb_cb(skb)->timestamp = jiffies;
sfq_inc(q, x);
if (slot->qlen == 1) { /* The flow is new */
if (q->tail == NULL) { /* It is the first flow */
@@ -402,11 +409,8 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
q->tail = slot;
slot->allot = q->scaled_quantum;
}
- if (++sch->q.qlen <= q->limit) {
- sch->bstats.bytes += qdisc_pkt_len(skb);
- sch->bstats.packets++;
+ if (++sch->q.qlen <= q->limit)
return NET_XMIT_SUCCESS;
- }
sfq_drop(sch);
return NET_XMIT_CN;
@@ -432,6 +436,7 @@ sfq_dequeue(struct Qdisc *sch)
sfq_index a, next_a;
struct sfq_slot *slot;
+restart:
/* No active slots */
if (q->tail == NULL)
return NULL;
@@ -455,12 +460,36 @@ next_slot:
next_a = slot->next;
if (a == next_a) {
q->tail = NULL; /* no more active slots */
+ /* last packet queued, dont even try to apply RED */
return skb;
}
q->tail->next = next_a;
} else {
slot->allot -= SFQ_ALLOT_SIZE(qdisc_pkt_len(skb));
}
+ if (red_delay) {
+ long delay = jiffies - qdisc_skb_cb(skb)->timestamp;
+
+ if (delay >= red_delay) {
+ long Px = delay * (0xFFFFFF / 100); /* 1 percent per jiffy */
+ if ((net_random() & 0xFFFFFF) < Px) {
+ if (INET_ECN_set_ce(skb)) {
+ /* no ecnmark counter yet :) */
+ sch->qstats.overlimits++;
+ } else {
+ /* penalize this flow : we drop the
+ * packet while we changed slot->allot
+ */
+ kfree_skb(skb);
+ /* no early_drop counter yet :) */
+ sch->qstats.drops++;
+ goto restart;
+ }
+ }
+ }
+ }
+ sch->bstats.bytes += qdisc_pkt_len(skb);
+ sch->bstats.packets++;
return skb;
}
next prev parent reply other threads:[~2011-03-24 13:32 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-13 1:40 Jonathan Morton
2011-03-24 1:03 ` Juliusz Chroboczek
2011-03-24 5:30 ` Dave Hart
2011-03-24 20:44 ` richard
2011-03-24 22:22 ` [Bloat] Packet drops, ECN and ECN+ [was: Thoughts on Stochastic Fair Blue] Juliusz Chroboczek
2011-03-25 19:22 ` Richard Scheffenegger
2011-04-03 16:35 ` [Bloat] Thoughts on Stochastic Fair Blue Juliusz Chroboczek
2011-04-03 18:03 ` Jonathan Morton
2011-03-24 11:59 ` Jim Gettys
2011-03-24 12:40 ` Jonathan Morton
2011-03-24 13:32 ` Eric Dumazet [this message]
2011-03-24 13:31 Dave Taht
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