netdev - Re: [PATCH RFC net-next 3/6] net_sched: sch

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Date:   Tue, 9 Jun 2020 08:00:38 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH RFC net-next 3/6] net_sched: sch_fq: multiple release time
 support



On 6/9/20 7:09 AM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> Optionally segment skbs on FQ enqueue, to later send segments at
> their individual delivery time.
> 
> Segmentation on enqueue is new for FQ, but already happens in TBF,
> CAKE and netem.
> 
> This slow patch should probably be behind a static_branch.
> 
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> ---
>  net/sched/sch_fq.c | 33 +++++++++++++++++++++++++++++++--
>  1 file changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c
> index 8f06a808c59a..a5e2c35bb557 100644
> --- a/net/sched/sch_fq.c
> +++ b/net/sched/sch_fq.c
> @@ -439,8 +439,8 @@ static bool fq_packet_beyond_horizon(const struct sk_buff *skb,
>  	return unlikely((s64)skb->tstamp > (s64)(q->ktime_cache + q->horizon));
>  }
>  
> -static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> -		      struct sk_buff **to_free)
> +static int __fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> +			struct sk_buff **to_free)
>  {
>  	struct fq_sched_data *q = qdisc_priv(sch);
>  	struct fq_flow *f;
> @@ -496,6 +496,35 @@ static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
>  	return NET_XMIT_SUCCESS;
>  }
>  
> +static int fq_enqueue(struct sk_buff *skb, struct Qdisc *sch,
> +		      struct sk_buff **to_free)
> +{
> +	struct sk_buff *segs, *next;
> +	int ret;
> +
> +	if (likely(!skb_is_gso(skb) || !skb->sk ||

You also need to check sk_fullsock(skb->sk), otherwise KMSAN might be unhappy.

> +		   !skb->sk->sk_txtime_multi_release))
> +		return __fq_enqueue(skb, sch, to_free);
> +
> +	segs = skb_gso_segment_txtime(skb);
> +	if (IS_ERR(segs))
> +		return qdisc_drop(skb, sch, to_free);
> +	if (!segs)
> +		return __fq_enqueue(skb, sch, to_free);
> +
> +	consume_skb(skb);

   This needs to be qdisc_drop(skb, sch, to_free) if queue is full, see below.

> +
> +	ret = NET_XMIT_DROP;
> +	skb_list_walk_safe(segs, segs, next) {
> +		skb_mark_not_on_list(segs);
> +		qdisc_skb_cb(segs)->pkt_len = segs->len;

This seems to under-estimate bytes sent. See qdisc_pkt_len_init() for details.

> +		if (__fq_enqueue(segs, sch, to_free) == NET_XMIT_SUCCESS)
> +			ret = NET_XMIT_SUCCESS;
> +	}

        if (unlikely(ret == NET_XMIT_DROP))
            qdisc_drop(skb, sch, to_free);
        else
            consume_skb(skb);

> +
> +	return ret;
> +}
> +
>  static void fq_check_throttled(struct fq_sched_data *q, u64 now)
>  {
>  	unsigned long sample;
>