netdev - Re: iproute2 / tbf with large burst seems broken again

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Message-Id: <200908251416.13888.denys@visp.net.lb>
Date:	Tue, 25 Aug 2009 14:16:13 +0300
From:	Denys Fedoryschenko <denys@...p.net.lb>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: iproute2 / tbf with large burst seems broken again

Done, tested, it doesn't stale and fix the issue but:

PPPoE_146 ~ # ./tc qdisc del dev ppp13 root;./tc qdisc add dev ppp13 root tbf 
rate 96000 burst 2048000 latency 500ms                                               

This one is ok
PPPoE_146 ~ # ./tc -s -d qdisc show dev ppp13
qdisc tbf 8005: root rate 96000bit burst 2000Kb/8 mpu 0b lat 500.0ms
 Sent 55260 bytes 65 pkt (dropped 0, overlimits 0 requeues 0)
 rate 0bit 0pps backlog 0b 0p requeues 0
qdisc ingress ffff: parent ffff:fff1 ----------------
 Sent 641055 bytes 2485 pkt (dropped 0, overlimits 0 requeues 0)
 rate 0bit 0pps backlog 0b 0p requeues 0

PPPoE_146 ~ # ./tc qdisc del dev ppp13 root;./tc qdisc add dev ppp13 root tbf 
rate 96000 burst 4096000 latency 500ms                                               

But this one maybe will overflow because of limitations in iproute2.

PPoE_146 ~ # ./tc -s -d qdisc show dev ppp13
qdisc tbf 8004: root rate 96000bit burst 797465b/8 mpu 0b lat 275.4s
 Sent 82867 bytes 123 pkt (dropped 0, overlimits 0 requeues 0)
 rate 0bit 0pps backlog 0b 0p requeues 0
qdisc ingress ffff: parent ffff:fff1 ----------------
 Sent 506821 bytes 1916 pkt (dropped 0, overlimits 0 requeues 0)
 rate 0bit 0pps backlog 0b 0p requeues 0

So maybe all of that just wrong way of using TBF.
At same time this means, if HTB and policers in filters done same way, that 
QoS in Linux cannot do similar to squid delay pools feature:

First 10Mb give with 1Mbit/s, then slow 64Kbit/s. If user use less than 64K - 
recharge with that unused bandwidth a "10 Mb / 1Mbit bucket".

On Tuesday 25 August 2009 12:41:20 Jarek Poplawski wrote:
> On Tue, Aug 25, 2009 at 09:00:35AM +0000, Jarek Poplawski wrote:
> > On Tue, Aug 25, 2009 at 08:43:06AM +0000, Jarek Poplawski wrote:
> > ...
> >
> > > since these 64 bits will be needed soon for higher rates anyway, I
> > > guess we could try some change like the patch below, if you find it
> > > works for you (I didn't test it yet.)
>
> I hope this time it works...
>
> Jarek P.
>
> --- (take 2)
>
>  net/sched/sch_tbf.c |   14 +++++++-------
>  1 files changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
> index e22dfe8..7d0fe69 100644
> --- a/net/sched/sch_tbf.c
> +++ b/net/sched/sch_tbf.c
> @@ -108,8 +108,8 @@ struct tbf_sched_data
>  	struct qdisc_rate_table	*P_tab;
>
>  /* Variables */
> -	long	tokens;			/* Current number of B tokens */
> -	long	ptokens;		/* Current number of P tokens */
> +	u32	tokens;			/* Current number of B tokens */
> +	u32	ptokens;		/* Current number of P tokens */
>  	psched_time_t	t_c;		/* Time check-point */
>  	struct Qdisc	*qdisc;		/* Inner qdisc, default - bfifo queue */
>  	struct qdisc_watchdog watchdog;	/* Watchdog timer */
> @@ -160,21 +160,21 @@ static struct sk_buff *tbf_dequeue(struct Qdisc* sch)
>
>  	if (skb) {
>  		psched_time_t now;
> -		long toks;
> -		long ptoks = 0;
> +		long long toks;
> +		long long ptoks = 0;
>  		unsigned int len = qdisc_pkt_len(skb);
>
>  		now = psched_get_time();
> -		toks = psched_tdiff_bounded(now, q->t_c, q->buffer);
> +		toks = min_t(u32, now - q->t_c, q->buffer);
>
>  		if (q->P_tab) {
>  			ptoks = toks + q->ptokens;
> -			if (ptoks > (long)q->mtu)
> +			if (ptoks > q->mtu)
>  				ptoks = q->mtu;
>  			ptoks -= L2T_P(q, len);
>  		}
>  		toks += q->tokens;
> -		if (toks > (long)q->buffer)
> +		if (toks > q->buffer)
>  			toks = q->buffer;
>  		toks -= L2T(q, len);


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