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Commit aa3e2199 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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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: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 914e5cea

net/sched/sch_sfq.c

+8 −12
Original line number Diff line number Diff line
@@ -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;

}