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authorEric Dumazet <eric.dumazet@gmail.com>2011-12-21 03:30:11 +0000
committerDavid S. Miller <davem@davemloft.net>2011-12-21 15:44:34 -0500
commit225d9b89c937633dfeec502741a174fe0bab5b9f (patch)
treed9a25ffaa6b4f14c0f3d624d3c654e9b0f7ec3bd
parent4e68ea26e76273cc62a981a414a8319a7f4c1077 (diff)
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sch_sfq: rehash queues in perturb timer
A known Out Of Order (OOO) problem hurts SFQ when timer changes perturbation value, since all new packets delivered to SFQ enqueue might end on different slots than previous in-flight packets. With round robin delivery, we can thus deliver packets in a different order. Since SFQ is limited to small amount of in-flight packets, we can rehash packets so that this OOO problem is fixed. This rehashing is performed only if internal flow classifier is in use. We now store in skb->cb[] the "struct flow_keys" so that we dont call skb_flow_dissect() again while rehashing. Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--net/sched/sch_sfq.c87
1 files changed, 81 insertions, 6 deletions
diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index 30cda707e40..d329a8a7235 100644
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -136,16 +136,30 @@ static inline struct sfq_head *sfq_dep_head(struct sfq_sched_data *q, sfq_index
return &q->dep[val - SFQ_SLOTS];
}
+/*
+ * In order to be able to quickly rehash our queue when timer changes
+ * q->perturbation, we store flow_keys in skb->cb[]
+ */
+struct sfq_skb_cb {
+ struct flow_keys keys;
+};
+
+static inline struct sfq_skb_cb *sfq_skb_cb(const struct sk_buff *skb)
+{
+ BUILD_BUG_ON(sizeof(skb->cb) <
+ sizeof(struct qdisc_skb_cb) + sizeof(struct sfq_skb_cb));
+ return (struct sfq_skb_cb *)qdisc_skb_cb(skb)->data;
+}
+
static unsigned int sfq_hash(const struct sfq_sched_data *q,
const struct sk_buff *skb)
{
- struct flow_keys keys;
+ const struct flow_keys *keys = &sfq_skb_cb(skb)->keys;
unsigned int hash;
- skb_flow_dissect(skb, &keys);
- hash = jhash_3words((__force u32)keys.dst,
- (__force u32)keys.src ^ keys.ip_proto,
- (__force u32)keys.ports, q->perturbation);
+ hash = jhash_3words((__force u32)keys->dst,
+ (__force u32)keys->src ^ keys->ip_proto,
+ (__force u32)keys->ports, q->perturbation);
return hash & (q->divisor - 1);
}
@@ -161,8 +175,10 @@ static unsigned int sfq_classify(struct sk_buff *skb, struct Qdisc *sch,
TC_H_MIN(skb->priority) <= q->divisor)
return TC_H_MIN(skb->priority);
- if (!q->filter_list)
+ if (!q->filter_list) {
+ skb_flow_dissect(skb, &sfq_skb_cb(skb)->keys);
return sfq_hash(q, skb) + 1;
+ }
*qerr = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
result = tc_classify(skb, q->filter_list, &res);
@@ -423,12 +439,71 @@ sfq_reset(struct Qdisc *sch)
kfree_skb(skb);
}
+/*
+ * When q->perturbation is changed, we rehash all queued skbs
+ * to avoid OOO (Out Of Order) effects.
+ * We dont use sfq_dequeue()/sfq_enqueue() because we dont want to change
+ * counters.
+ */
+static void sfq_rehash(struct sfq_sched_data *q)
+{
+ struct sk_buff *skb;
+ int i;
+ struct sfq_slot *slot;
+ struct sk_buff_head list;
+
+ __skb_queue_head_init(&list);
+
+ for (i = 0; i < SFQ_SLOTS; i++) {
+ slot = &q->slots[i];
+ if (!slot->qlen)
+ continue;
+ while (slot->qlen) {
+ skb = slot_dequeue_head(slot);
+ sfq_dec(q, i);
+ __skb_queue_tail(&list, skb);
+ }
+ q->ht[slot->hash] = SFQ_EMPTY_SLOT;
+ }
+ q->tail = NULL;
+
+ while ((skb = __skb_dequeue(&list)) != NULL) {
+ unsigned int hash = sfq_hash(q, skb);
+ sfq_index x = q->ht[hash];
+
+ slot = &q->slots[x];
+ if (x == SFQ_EMPTY_SLOT) {
+ x = q->dep[0].next; /* get a free slot */
+ q->ht[hash] = x;
+ slot = &q->slots[x];
+ slot->hash = hash;
+ }
+ slot_queue_add(slot, skb);
+ sfq_inc(q, x);
+ if (slot->qlen == 1) { /* The flow is new */
+ if (q->tail == NULL) { /* It is the first flow */
+ slot->next = x;
+ } else {
+ slot->next = q->tail->next;
+ q->tail->next = x;
+ }
+ q->tail = slot;
+ slot->allot = q->scaled_quantum;
+ }
+ }
+}
+
static void sfq_perturbation(unsigned long arg)
{
struct Qdisc *sch = (struct Qdisc *)arg;
struct sfq_sched_data *q = qdisc_priv(sch);
+ spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
+ spin_lock(root_lock);
q->perturbation = net_random();
+ if (!q->filter_list && q->tail)
+ sfq_rehash(q);
+ spin_unlock(root_lock);
if (q->perturb_period)
mod_timer(&q->perturb_timer, jiffies + q->perturb_period);