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

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Date:   Tue, 9 Jun 2020 08:10:34 -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 8:00 AM, Eric Dumazet wrote:
> 
> 
> 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);

Maybe not qdisc_drop() (qdisc drop counters are already updated)
but at least kfree_skb() so that drop monitor is not fooled.

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