From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [RFC PATCH 01/13] net: sched: allow qdiscs to handle locking
Date: Wed, 17 Aug 2016 15:34:02 -0700
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	 <20160817193338.27032.71493.stgit@john-Precision-Tower-5810>
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Cc: xiyou.wangcong@gmail.com, jhs@mojatatu.com,
	alexei.starovoitov@gmail.com, brouer@redhat.com,
	john.r.fastabend@intel.com, netdev@vger.kernel.org,
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To: John Fastabend <john.fastabend@gmail.com>
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On Wed, 2016-08-17 at 12:33 -0700, John Fastabend wrote:


> diff --git a/net/core/dev.c b/net/core/dev.c
> index 4ce07dc..5db395d 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3076,6 +3076,26 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
>  	int rc;
>  
>  	qdisc_calculate_pkt_len(skb, q);
> +
> +	if (q->flags & TCQ_F_NOLOCK) {
> +		if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) {
> +			__qdisc_drop(skb, &to_free);
> +			rc = NET_XMIT_DROP;
> +		} else if ((q->flags & TCQ_F_CAN_BYPASS) && !qdisc_qlen(q)) {

For a lockless qdisc, do you believe TCQ_F_CAN_BYPASS is still a gain ?

Also !qdisc_qlen(q) looks racy anyway ?

> +			qdisc_bstats_cpu_update(q, skb);
> +			if (sch_direct_xmit(skb, q, dev, txq, root_lock, true))
> +				__qdisc_run(q);
> +			rc = NET_XMIT_SUCCESS;
> +		} else {
> +			rc = q->enqueue(skb, q, &to_free) & NET_XMIT_MASK;
> +			__qdisc_run(q);
> +		}
> +
> +		if (unlikely(to_free))
> +			kfree_skb_list(to_free);
> +		return rc;
> +	}
> +