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Date: Sat, 12 Nov 2011 10:45:46 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: Dave Taht <dave.taht@...il.com>
Cc: Denys Fedoryshchenko <denys@....net.sa>,
Helmut Schaa <helmut.schaa@...glemail.com>,
Johannes Berg <johannes@...solutions.net>,
netdev <netdev@...r.kernel.org>,
linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: creating netdev queues on the fly?
Le vendredi 11 novembre 2011 à 12:02 +0100, Eric Dumazet a écrit :
> I would see a new Qdisc/Class property, like the rate estimator, that we
> can attach to any Qdisc/Class with a new tc option.
>
> Even without any limit enforcing (might be Random Early Detection by the
> way), it could be used to get a Queue Delay estimation, using EWMA
>
> avqdelay = avqdelay*(1-W) + qdelay*W;
> W = 2^(-ewma_log);
>
> tc [ qdisc | class] add [...] [est 1sec 8sec] [delayest ewma_log ] ..
>
> tc -s -d qdisc ...
> qdisc htb 1: root refcnt 2 r2q 10 default 1 direct_packets_stat 0 ver 3.17
> Sent 3596219 bytes 2567 pkt (dropped 238, overlimits 3797 requeues 0)
> rate 2557Kbit 215pps backlog 0b 0p requeues 0
> delay 91ms
>
>
I coded the thing (delayest at qdisc level) and got interesting values,
for example with following HTB setup :
DEV=eth3
MTU=1500
rate=10mbit
EST="est 1sec 8sec delayest 6"
tc qdisc del dev $DEV root
tc qdisc add dev $DEV root handle 1: ${EST} \
htb default 1
tc class add dev $DEV parent 1: classid 1:1 htb \
rate ${rate} mtu 40000 quantum 80000
tc qdisc add dev $DEV parent 1:1 handle 10: ${EST} pfifo limit 3
With light trafic on my x86_64 machine I have :
# tcnew -s -d qdisc show dev eth3
qdisc htb 1: root refcnt 17 r2q 10 default 1 direct_packets_stat 0 ver 3.17
Sent 78216 bytes 569 pkt (dropped 0, overlimits 0 requeues 0)
rate 9040bit 13pps backlog 0b 0p requeues 0
delay 1126 ns log 6
qdisc pfifo 10: parent 1:1 limit 3p
Sent 78216 bytes 569 pkt (dropped 0, overlimits 0 requeues 0)
rate 9040bit 13pps backlog 0b 0p requeues 0
delay 731 ns log 6
Wow, 1126ns of overhead per packet...
This is the prototype kernel patch I used on top of net-next :
diff --git a/include/linux/gen_stats.h b/include/linux/gen_stats.h
index 552c8a0..5ad57a6 100644
--- a/include/linux/gen_stats.h
+++ b/include/linux/gen_stats.h
@@ -63,5 +63,16 @@ struct gnet_estimator {
unsigned char ewma_log;
};
+/**
+ * struct gnet_qdelay - queue delay configuration / reports
+ * @avdelay: average queue delay in ns
+ * @limit: packets delayed more than this value are dropped
+ * @avdelaylog: the log of measurement window weight
+ */
+struct gnet_qdelay {
+ __u64 avdelay;
+ __u64 limit;
+ __u32 avdelaylog;
+};
#endif /* __LINUX_GEN_STATS_H */
diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index 8e872ea..61c66ec 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -484,6 +484,7 @@ enum {
TCA_FCNT,
TCA_STATS2,
TCA_STAB,
+ TCA_QDELAY,
__TCA_MAX
};
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index f6bb08b..e293228 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -42,6 +42,13 @@ struct qdisc_size_table {
u16 data[];
};
+/*
+ * qdisc/class avdelay is computed using EWMA, with a fixed factor of 16
+ * Only the weight is a parameter (avdelaylog)
+ * With u64 values, this leaves 48 bits, a max of 281474 seconds.
+ */
+#define TCQ_AVDELAY_FACTOR 16
+
struct Qdisc {
int (*enqueue)(struct sk_buff *skb, struct Qdisc *dev);
struct sk_buff * (*dequeue)(struct Qdisc *dev);
@@ -50,8 +57,11 @@ struct Qdisc {
#define TCQ_F_INGRESS 2
#define TCQ_F_CAN_BYPASS 4
#define TCQ_F_MQROOT 8
+#define TCQ_F_QDELAY 0x10
#define TCQ_F_WARN_NONWC (1 << 16)
- int padded;
+ u8 padded;
+ u8 avdelaylog; /* avdelay EWMA weight */
+ u8 _pad[2];
const struct Qdisc_ops *ops;
struct qdisc_size_table __rcu *stab;
struct list_head list;
@@ -80,6 +90,10 @@ struct Qdisc {
struct gnet_stats_basic_packed bstats;
unsigned int __state;
struct gnet_stats_queue qstats;
+
+ /* average queue delay in ns << TCQ_AVDELAY_FACTOR */
+ u64 avdelay;
+
struct rcu_head rcu_head;
spinlock_t busylock;
u32 limit;
@@ -219,6 +233,9 @@ struct tcf_proto {
};
struct qdisc_skb_cb {
+#ifdef CONFIG_NET_SCHED_QDELAY
+ ktime_t enqueue_time;
+#endif
unsigned int pkt_len;
long data[];
};
@@ -467,6 +484,14 @@ static inline void qdisc_bstats_update(struct Qdisc *sch,
const struct sk_buff *skb)
{
bstats_update(&sch->bstats, skb);
+#ifdef CONFIG_NET_SCHED_QDELAY
+ if (sch->flags & TCQ_F_QDELAY) {
+ u64 delay = ktime_to_ns(ktime_sub(ktime_get(),
+ qdisc_skb_cb(skb)->enqueue_time));
+ delay <<= TCQ_AVDELAY_FACTOR;
+ sch->avdelay += (delay >> sch->avdelaylog) - (sch->avdelay >> sch->avdelaylog);
+ }
+#endif
}
static inline int __qdisc_enqueue_tail(struct sk_buff *skb, struct Qdisc *sch,
diff --git a/net/core/dev.c b/net/core/dev.c
index 6ba50a1..587534d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2402,6 +2402,13 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
int rc;
qdisc_skb_cb(skb)->pkt_len = skb->len;
+
+#ifdef CONFIG_NET_SCHED_QDELAY
+ qdisc_skb_cb(skb)->enqueue_time.tv64 = 0;
+ if (q->flags & TCQ_F_QDELAY)
+ qdisc_skb_cb(skb)->enqueue_time = ktime_get();
+#endif
+
qdisc_calculate_pkt_len(skb, q);
/*
* Heuristic to force contended enqueues to serialize on a
diff --git a/net/sched/Kconfig b/net/sched/Kconfig
index 2590e91..028f882 100644
--- a/net/sched/Kconfig
+++ b/net/sched/Kconfig
@@ -470,6 +470,17 @@ config NET_CLS_ACT
A recent version of the iproute2 package is required to use
extended matches.
+config NET_SCHED_QDELAY
+ bool "QDISC/CLASS queue delay Estimators and Limits"
+ ---help---
+ Say Y here if you want to be able to track queue delays, and
+ be able to drop packets if they stay in a queue a too long time.
+ It adds some overhead per packet, since it needs to get precise
+ time at enqueue and dequeue time.
+
+ A recent version of the iproute2 package is required to use
+ extended matches.
+
config NET_ACT_POLICE
tristate "Traffic Policing"
depends on NET_CLS_ACT
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index dca6c1a..212fba9 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -842,6 +842,17 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue,
}
rcu_assign_pointer(sch->stab, stab);
}
+ if (tca[TCA_QDELAY]) {
+ struct gnet_qdelay *parm = nla_data(tca[TCA_QDELAY]);
+ err = -EINVAL;
+ if (nla_len(tca[TCA_QDELAY]) < sizeof(*parm))
+ goto err_out4;
+ sch->avdelaylog = parm->avdelaylog;
+ sch->flags |= TCQ_F_QDELAY;
+ } else { /* temporary testing */
+ sch->avdelaylog = 6;
+ sch->flags |= TCQ_F_QDELAY;
+ }
if (tca[TCA_RATE]) {
spinlock_t *root_lock;
@@ -1206,6 +1217,16 @@ static int tc_fill_qdisc(struct sk_buff *skb, struct Qdisc *q, u32 clid,
if (stab && qdisc_dump_stab(skb, stab) < 0)
goto nla_put_failure;
+#ifdef CONFIG_NET_SCHED_QDELAY
+ if (q->flags & TCQ_F_QDELAY) {
+ struct gnet_qdelay qdelay;
+
+ memset(&qdelay, 0, sizeof(qdelay));
+ qdelay.avdelay = q->avdelay >> TCQ_AVDELAY_FACTOR;
+ qdelay.avdelaylog = q->avdelaylog;
+ NLA_PUT(skb, TCA_QDELAY, sizeof(qdelay), &qdelay);
+ }
+#endif
if (gnet_stats_start_copy_compat(skb, TCA_STATS2, TCA_STATS, TCA_XSTATS,
qdisc_root_sleeping_lock(q), &d) < 0)
goto nla_put_failure;
--
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