netdev - Re: [PATCH net-next 2/3] udp: avoid a cache miss on dequeue

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Date:   Wed, 31 May 2017 10:00:43 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next 2/3] udp: avoid a cache miss on dequeue

On Mon, 2017-05-29 at 17:27 +0200, Paolo Abeni wrote:
> Since UDP no more uses sk->destructor, we can clear completely
> the skb head state before enqueuing.

...

> @@ -1739,6 +1740,9 @@ static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
>  		sk_mark_napi_id_once(sk, skb);
>  	}
>  
> +	/* drop all pending head states; dst, nf and sk are dropped by caller */
> +	secpath_reset(skb);
> +

I wonder if using skb_release_head_state() would be more appropriate ?

Surely more descriptive and probably not more expensive since all
cache lines should be already hot at this point.

>  	rc = __udp_enqueue_schedule_skb(sk, skb);
>  	if (rc < 0) {
>  		int is_udplite = IS_UDPLITE(sk);