Re: [RFC PATCH] net: sched: convert qdisc linked list to hashtable (was Re: Deleting child qdisc doesn't reset parent to default qdisc?)

[Eric Dumazet]

On Thu, 2016-07-07 at 11:04 +0200, Jiri Kosina wrote:

> 
> 
> From: Jiri Kosina <jkosina@xxxxxxx>
> Subject: [PATCH] net: sched: convert qdisc linked list to hashtable
> 
> Convert the per-device linked list into a hashtable. The primary motivation
> for this change is that currently, we're not tracking all the qdiscs in
> hierarchy (e.g. excluding default qdiscs), as the lookup performed over the
> linked list by qdisc_match_from_root() is rather expensive.

...

>  	}
> @@ -1440,6 +1441,7 @@ static int tc_dump_qdisc_root(struct Qdisc *root, struct sk_buff *skb,
>  {
>  	int ret = 0, q_idx = *q_idx_p;
>  	struct Qdisc *q;
> +	int b;
>  
>  	if (!root)
>  		return 0;
> @@ -1454,7 +1456,7 @@ static int tc_dump_qdisc_root(struct Qdisc *root, struct sk_buff *skb,
>  			goto done;
>  		q_idx++;
>  	}
> -	list_for_each_entry(q, &root->list, list) {
> +	hash_for_each(qdisc_dev(root)->qdisc_hash, b, q, hash) {
>  		if (q_idx < s_q_idx) {
>  			q_idx++;
>  			continue;
> @@ -1771,6 +1773,7 @@ static int tc_dump_tclass_root(struct Qdisc *root, struct sk_buff *skb,
>  			       int *t_p, int s_t)
>  {
>  	struct Qdisc *q;
> +	int b;
>  
>  	if (!root)
>  		return 0;
> @@ -1778,7 +1781,7 @@ static int tc_dump_tclass_root(struct Qdisc *root, struct sk_buff *skb,
>  	if (tc_dump_tclass_qdisc(root, skb, tcm, cb, t_p, s_t) < 0)
>  		return -1;
>  
> -	list_for_each_entry(q, &root->list, list) {
> +	hash_for_each_rcu(qdisc_dev(root)->qdisc_hash, b, q, hash) {
>  		if (tc_dump_tclass_qdisc(q, skb, tcm, cb, t_p, s_t) < 0)
>  			return -1;
>  	}


Not sure why you used the rcu version here, but the non rcu version in
tc_dump_qdisc_root()

Thanks.