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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>
This commit is contained in:
Eric Dumazet 2010-12-20 13:18:16 -08:00 committed by David S. Miller
parent 914e5cea14
commit aa3e219997
1 changed files with 8 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
net/sched/sch_sfq.c
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@ -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;
}