netdev - Re: [PATCH net-next RESEND] sched: sfq: drop packets after root qdisc lock is released

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Date:   Fri, 25 Aug 2017 05:49:37 -0700
From:   Eric Dumazet <erdnetdev@...il.com>
To:     gfree.wind@....163.com
Cc:     jhs@...atatu.com, xiyou.wangcong@...il.com, jiri@...nulli.us,
        davem@...emloft.net, edumazet@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next RESEND] sched: sfq: drop packets after root
 qdisc lock is released

On Fri, 2017-08-25 at 15:43 +0800, gfree.wind@....163.com wrote:
> From: Gao Feng <gfree.wind@....163.com>
> 
> The commit 520ac30f4551 ("net_sched: drop packets after root qdisc lock
> is released) made a big change of tc for performance. But there are
> some points which are not changed in SFQ enqueue operation.
> 1. Fail to find the SFQ hash slot;
> 2. When the queue is full;
> 
> Now use qdisc_drop instead free skb directly.


Thanks for doing this work.

I have one comment

> 
> Signed-off-by: Gao Feng <gfree.wind@....163.com>
> ---
>  net/sched/sch_sfq.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
> index 82469ef..8841f4d 100644
> --- a/net/sched/sch_sfq.c
> +++ b/net/sched/sch_sfq.c
> @@ -292,7 +292,7 @@ static inline void slot_queue_add(struct sfq_slot *slot, struct sk_buff *skb)
>  	slot->skblist_prev = skb;
>  }
>  
> -static unsigned int sfq_drop(struct Qdisc *sch)
> +static unsigned int sfq_drop(struct Qdisc *sch, struct sk_buff **to_free)
>  {
>  	struct sfq_sched_data *q = qdisc_priv(sch);
>  	sfq_index x, d = q->cur_depth;
> @@ -310,9 +310,13 @@ static unsigned int sfq_drop(struct Qdisc *sch)
>  		slot->backlog -= len;
>  		sfq_dec(q, x);
>  		sch->q.qlen--;
> -		qdisc_qstats_drop(sch);
>  		qdisc_qstats_backlog_dec(sch, skb);
> -		kfree_skb(skb);
> +		if (likely(to_free)) {
> +			qdisc_drop(skb, sch, to_free);
> +		} else {
> +			qdisc_qstats_drop(sch);
> +			kfree_skb(skb);

                         rtnl_kfree_skbs(skb, skb);  ?

Or even better provide a non NULL to_free from sfq_change()

Then call rtnl_kfree_skbs() once from sfq_change()


> +		}
>  		return len;
>  	}
>  
> @@ -360,7 +364,7 @@ static int sfq_headdrop(const struct sfq_sched_data *q)
>  	if (hash == 0) {
>  		if (ret & __NET_XMIT_BYPASS)
>  			qdisc_qstats_drop(sch);
> -		kfree_skb(skb);
> +		__qdisc_drop(skb, to_free);
>  		return ret;
>  	}
>  	hash--;
> @@ -465,7 +469,7 @@ static int sfq_headdrop(const struct sfq_sched_data *q)
>  		return NET_XMIT_SUCCESS;
>  
>  	qlen = slot->qlen;
> -	dropped = sfq_drop(sch);
> +	dropped = sfq_drop(sch, to_free);
>  	/* Return Congestion Notification only if we dropped a packet
>  	 * from this flow.
>  	 */
> @@ -675,7 +679,7 @@ static int sfq_change(struct Qdisc *sch, struct nlattr *opt)
>  
>  	qlen = sch->q.qlen;
>  	while (sch->q.qlen > q->limit)
> -		dropped += sfq_drop(sch);
> +		dropped += sfq_drop(sch, NULL);
>  	qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped);
>  
>  	del_timer(&q->perturb_timer);