netdev - [PATCH v2] net_sched: sch_sfq: fix allot handling

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Date:	Wed, 15 Dec 2010 17:40:56 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Jarek Poplawski <jarkao2@...il.com>
Subject: [PATCH v2] net_sched: sch_sfq: fix allot handling

Le mercredi 15 décembre 2010 à 17:27 +0100, Eric Dumazet a écrit :

> Hmm, you may be right, thanks a lot for reviewing !
> 
> I noticed that with normal quantum (1514), my SFQ setup was sending two
> full frames per flow after my patch, so was about to prepare a new
> version ;)
> 
> I'll post a v2 shortly.

Indeed, the missing init in sfq_enqueue() is enough to solve the
problem : 

[PATCH v2] 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.

class sfq 11:2e4 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 4p requeues 0 
 allot -1166 

class sfq 11:2f7 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 3p requeues 0 
 allot -1166 

class sfq 11:313 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 3p requeues 0 
 allot -1220 

class sfq 11:335 parent 11: 
 (dropped 0, overlimits 0 requeues 0) 
 backlog 0b 4p requeues 0 
 allot -1166 


Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
 net/sched/sch_sfq.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
index 3cf478d..065a2a5 100644
--- a/net/sched/sch_sfq.c
+++ b/net/sched/sch_sfq.c
@@ -321,14 +321,13 @@ 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);


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