netdev - Re: [PATCH RFC 3/3] net_sched: Add size table for qdiscs

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Date:	Thu, 17 Jul 2008 21:02:31 +0300
From:	"Jussi Kivilinna" <jussi.kivilinna@...et.fi>
To:	"Patrick McHardy" <kaber@...sh.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH RFC 3/3] net_sched: Add size table for qdiscs

Quoting "Patrick McHardy" <kaber@...sh.net>:

> Jussi Kivilinna wrote:
>> diff --git a/include/linux/pkt_sched.h b/include/linux/pkt_sched.h
>> index dbb7ac3..eae53bf 100644
>> --- a/include/linux/pkt_sched.h
>> +++ b/include/linux/pkt_sched.h
>> @@ -85,6 +85,27 @@ struct tc_ratespec
>>  #define TC_RTAB_SIZE	1024
>> +struct tc_sizespec {
>> +	unsigned char	cell_log;
>> +	unsigned char	size_log;
>> +	short		cell_align;
>> +	int		overhead;
>> +	unsigned	linklayer;
>> +	unsigned	mpu;
>> +	unsigned	mtu;
>> +};
>
> Please use "unsigned int".
>

Ok.

>> +
>> +#define TC_STAB_DATA_SIZE 1024
>> +
>> +enum {
>> +	TCA_STAB_UNSPEC,
>> +	TCA_STAB_BASE,
>> +	TCA_STAB_DATA,
>> +	__TCA_STAB_MAX
>> +};
>
> Since you already split the STAB into a base and a data
> structure, wouldn't it make sense to have the data size
> dynamic for user-defined granularity?
>

Yes, it would.

>> +static LIST_HEAD(qdisc_stab_list);
>> +
>> +static const struct nla_policy stab_policy[TCA_STAB_MAX + 1] = {
>> +	[TCA_STAB_BASE]	= { .len = sizeof(struct tc_sizespec) },
>> +	[TCA_STAB_DATA] = { .type = NLA_BINARY, .len = TC_STAB_DATA_SIZE },
>> +};
>> +
>> +static struct qdisc_size_table *qdisc_get_stab(struct nlattr *opt,  
>>  int *err)
>> +{
>> +	struct nlattr *tb[TCA_STAB_MAX + 1];
>> +	struct qdisc_size_table *stab;
>> +	struct tc_sizespec *s;
>> +	u16 *tab;
>> +
>> +	*err = nla_parse_nested(tb, TCA_STAB_MAX, opt, stab_policy);
>> +	if (*err < 0)
>> +		return NULL;
>
> ERR_PTR is cleaner than pointer return values IMO.
>

Ok.

>> diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
>> index bc9d6af..f75ba82 100644
>> --- a/net/sched/sch_netem.c
>> +++ b/net/sched/sch_netem.c
>> @@ -84,7 +84,7 @@ struct netem_skb_cb {
>>  static inline struct netem_skb_cb *netem_skb_cb(struct sk_buff *skb)
>> {
>> -	return (struct netem_skb_cb *)skb->cb;
>> +	return (struct netem_skb_cb *)qdisc_skb_cb(skb)->data;
>> }
>
> A BUILD_BUG_ON to make sure the skb->cb size is not exceeded would
> be good to have.
>

Ok.

>> /* init_crandom - initialize correlated random number generator
>> @@ -189,6 +189,7 @@ static int netem_enqueue(struct sk_buff *skb,   
>> struct Qdisc *sch)
>> 		u32 dupsave = q->duplicate; /* prevent duplicating a dup... */
>> 		q->duplicate = 0;
>> +		qdisc_root_init_tx_len(skb2, rootq);
>> 		qdisc_enqueue(skb2, rootq);
>
> How about adding qdisc_enqueue_root() to perform both these steps
> (its similar to net/core/dev.c).
>

Sure.

>> diff --git a/net/sched/sch_tbf.c b/net/sched/sch_tbf.c
>> index 1e3d52e..862c0e3 100644
>> --- a/net/sched/sch_tbf.c
>> +++ b/net/sched/sch_tbf.c
>> @@ -123,9 +123,9 @@ static int tbf_enqueue(struct sk_buff *skb,   
>> struct Qdisc* sch)
>> 	struct tbf_sched_data *q = qdisc_priv(sch);
>> 	int ret;
>> -	/* qdisc_tx_len() before qdisc_enqueue() wrapper, might return different
>> -	 * length than after wrapper. Should recalculate tx_len here if q->qdisc
>> -	 * has size table? */
>> +	if (q->qdisc->stab)
>> +		qdisc_calculate_tx_len(skb, q->qdisc->stab);
>> +
>
> I don't think this will help, the inner qdisc might again have
> an inner qdisc that increases the size. So this probably needs
> to be handled during dequeue.
>

I don't quite follow you here, what needs to be handled during  
dequeue? tbf's q->max_size check?

>> 	if (qdisc_tx_len(skb) > q->max_size) {
>> 		sch->qstats.drops++;
>> #ifdef CONFIG_NET_CLS_ACT
>>
>
>
>



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