net_sched: sch_sfq: fix allot handling

When deploying SFQ/IFB here at work, I found the allot management was
pretty wrong in sfq, even changing allot from short to int...

We should init allot for each new flow, not using a previous value found
in slot.

Before patch, I saw bursts of several packets per flow, apparently
denying the default "quantum 1514" limit I had on my SFQ class.

class sfq 11:1 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 7p requeues 0 
 allot 11546 

class sfq 11:46 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 1p requeues 0 
 allot -23873 

class sfq 11:78 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 5p requeues 0 
 allot 11393 

After patch, better fairness among each flow, allot limit being
respected, allot is positive :

class sfq 11:e parent 11: 
 (dropped 0, overlimits 0 requeues 86) 
 backlog 0b 3p requeues 86 
 allot 596 

class sfq 11:94 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 3p requeues 0 
 allot 1468 

class sfq 11:a4 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 4p requeues 0 
 allot 650 

class sfq 11:bb parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 3p requeues 0 
 allot 596 

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 12 deletions

diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index 3cf478d012dd..7150705f1d0b 100644
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -270,7 +270,6 @@ static unsigned int sfq_drop(struct Qdisc *sch)
                 /* It is difficult to believe, but ALL THE SLOTS HAVE LENGTH 1. */
                 d = q->next[q->tail];
                 q->next[q->tail] = q->next[d];
-                q->allot[q->next[d]] += q->quantum;
                 skb = q->qs[d].prev;
                 len = qdisc_pkt_len(skb);
                 __skb_unlink(skb, &q->qs[d]);
@@ -321,14 +320,13 @@ sfq_enqueue(struct sk_buff *skb, struct Qdisc *sch)
         sfq_inc(q, x);
         if (q->qs[x].qlen == 1) {               /* The flow is new */
                 if (q->tail == SFQ_DEPTH) {     /* It is the first flow */
-                        q->tail = x;
                         q->next[x] = x;
-                        q->allot[x] = q->quantum;
                 } else {
                         q->next[x] = q->next[q->tail];
                         q->next[q->tail] = x;
-                        q->tail = x;
                 }
+                q->tail = x;
+                q->allot[x] = q->quantum;
         }
         if (++sch->q.qlen <= q->limit) {
                 sch->bstats.bytes += qdisc_pkt_len(skb);
@@ -359,13 +357,13 @@ sfq_dequeue(struct Qdisc *sch)
 {
         struct sfq_sched_data *q = qdisc_priv(sch);
         struct sk_buff *skb;
-        sfq_index a, old_a;
+        sfq_index a, next_a;
 
         /* No active slots */
         if (q->tail == SFQ_DEPTH)
                 return NULL;
 
-        a = old_a = q->next[q->tail];
+        a = q->next[q->tail];
 
         /* Grab packet */
         skb = __skb_dequeue(&q->qs[a]);
@@ -376,17 +374,15 @@ sfq_dequeue(struct Qdisc *sch)
         /* Is the slot empty? */
         if (q->qs[a].qlen == 0) {
                 q->ht[q->hash[a]] = SFQ_DEPTH;
-                a = q->next[a];
-                if (a == old_a) {
+                next_a = q->next[a];
+                if (a == next_a) {
                         q->tail = SFQ_DEPTH;
                         return skb;
                 }
-                q->next[q->tail] = a;
-                q->allot[a] += q->quantum;
+                q->next[q->tail] = next_a;
         } else if ((q->allot[a] -= qdisc_pkt_len(skb)) <= 0) {
-                q->tail = a;
-                a = q->next[a];
                 q->allot[a] += q->quantum;
+                q->tail = a;
         }
         return skb;
 }