Subject: Re: [RFC PATCH] sched: Fix resource limiting in pfifo_fast

From: Eric Dumazet <[email-masked]>
Date: Sun, 30 Aug 2009 08:54:53 +0200

Krishna Kumar a écrit :
> From: Krishna Kumar <[email-masked]>
> 
> pfifo_fast_enqueue has this check:
>         if (skb_queue_len(list) < qdisc_dev(qdisc)->tx_queue_len) {
> 
> which allows each band to enqueue upto tx_queue_len skbs for a
> total of 3*tx_queue_len skbs. I am not sure if this was the
> intention of limiting in qdisc.

Yes I noticed that and said to myself :
This was to let high priority packets have their own limit,
independent on fact that low priority packets filled their queue.

> 
> Patch compiled and 32 simultaneous netperf testing ran fine. Also:
> # tc -s qdisc show dev eth2
> qdisc pfifo_fast 0: root bands 3 priomap  1 2 2 2 1 2 0 0 1 1 1 1 1 1 1 1
>  Sent 16835026752 bytes 373116 pkt (dropped 0, overlimits 0 requeues 25) 
>  rate 0bit 0pps backlog 0b 0p requeues 25 
> 
> (I am taking next week off, so sorry for any delay in responding)
> 
> Signed-off-by: Krishna Kumar <[email-masked]>
> ---
> 
>  net/sched/sch_generic.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff -ruNp org/net/sched/sch_generic.c new/net/sched/sch_generic.c
> --- org/net/sched/sch_generic.c	2009-08-30 11:18:23.000000000 +0530
> +++ new/net/sched/sch_generic.c	2009-08-30 11:21:50.000000000 +0530
> @@ -432,11 +432,11 @@ static inline struct sk_buff_head *band2
>  
>  static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc* qdisc)
>  {
> -	int band = prio2band[skb->priority & TC_PRIO_MAX];
> -	struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
> -	struct sk_buff_head *list = band2list(priv, band);
> +	if (skb_queue_len(&qdisc->q) < qdisc_dev(qdisc)->tx_queue_len) {
> +		int band = prio2band[skb->priority & TC_PRIO_MAX];
> +		struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
> +		struct sk_buff_head *list = band2list(priv, band);
>  
> -	if (skb_queue_len(list) < qdisc_dev(qdisc)->tx_queue_len) {
>  		priv->bitmap |= (1 << band);
>  		qdisc->q.qlen++;
>  		return __qdisc_enqueue_tail(skb, qdisc, list);