netdev - Re: [PATCH v6 2/4] net: moxa: replace build_skb() with netdev_alloc_skb_ip

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Date:	Tue, 26 Aug 2014 11:04:30 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Jonas Jensen <jonas.jensen@...il.com>, netdev@...r.kernel.org,
	f.fainelli@...il.com, eric.dumazet@...il.com,
	linux-kernel@...r.kernel.org, mirqus@...il.com, davem@...emloft.net
Subject: Re: [PATCH v6 2/4] net: moxa: replace build_skb() with netdev_alloc_skb_ip_align() / memcpy()

On Monday 25 August 2014 16:22:22 Jonas Jensen wrote:
> @@ -226,13 +226,15 @@ static int moxart_rx_poll(struct napi_struct *napi, int budget)
>                 if (len > RX_BUF_SIZE)
>                         len = RX_BUF_SIZE;
>  
> -               skb = build_skb(priv->rx_buf[rx_head], priv->rx_buf_size);
> +               skb = netdev_alloc_skb_ip_align(ndev, len);
> +
>                 if (unlikely(!skb)) {
> -                       net_dbg_ratelimited("build_skb failed\n");
> +                       net_dbg_ratelimited("netdev_alloc_skb_ip_align failed\n");
>                         priv->stats.rx_dropped++;
>                         priv->stats.rx_errors++;
>                 }
>  
> +               memcpy(skb->data, priv->rx_buf[rx_head], len);
>                 skb_put(skb, len);
>                 skb->protocol = eth_type_trans(skb, ndev);
>                 napi_gro_receive(&priv->napi, skb);

While this seems correct, I wonder why you don't do the normal approach of
dequeuing the skb from the chain and adding a newly allocated skb to it to
save the memcpy.

	Arnd
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