linux-kernel - Re: [net-next PATCH v4 4/7] net: ravb: Refactor GbEth RX code path

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Date: Wed, 29 May 2024 21:30:08 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Paul Barker <paul.barker.ct@...renesas.com>, "David S. Miller"
	<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
	<kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
CC: Biju Das <biju.das.jz@...renesas.com>, Claudiu Beznea
	<claudiu.beznea.uj@...renesas.com>, Yoshihiro Shimoda
	<yoshihiro.shimoda.uh@...esas.com>, <netdev@...r.kernel.org>,
	<linux-renesas-soc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [net-next PATCH v4 4/7] net: ravb: Refactor GbEth RX code path

On 5/28/24 6:03 PM, Paul Barker wrote:

> We can reduce code duplication in ravb_rx_gbeth().
> 
> Signed-off-by: Paul Barker <paul.barker.ct@...renesas.com>
[...]

> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
> index 7df7d2e93a3a..c9c5cc641589 100644
> --- a/drivers/net/ethernet/renesas/ravb_main.c
> +++ b/drivers/net/ethernet/renesas/ravb_main.c
> @@ -817,47 +817,54 @@ static int ravb_rx_gbeth(struct net_device *ndev, int budget, int q)
>  				stats->rx_missed_errors++;
>  		} else {
>  			die_dt = desc->die_dt & 0xF0;
> +			skb = ravb_get_skb_gbeth(ndev, entry, desc);
>  			switch (die_dt) {

   Why not do instead (as I've asked you alraedy):

			case DT_FSTART:
				priv->rx_1st_skb = skb;
				fallthrough;

>  			case DT_FSINGLE:
> -				skb = ravb_get_skb_gbeth(ndev, entry, desc);


> +			case DT_FSTART:
> +				/* Start of packet:
> +				 * Set initial data length.
> +				 */

   Please consider turning that block comment into one-liner...

>  				skb_put(skb, desc_len);
> +
> +				/* Save this SKB if the packet spans multiple
> +				 * descriptors.
> +				 */

   This one too...
   (The current line length limit is 100 columns.)

> +				if (die_dt == DT_FSTART)
> +					priv->rx_1st_skb = skb;

   This needs to be done under *case* DT_FSTART above instead...

> +				break;
> +
> +			case DT_FMID:
> +			case DT_FEND:
> +				/* Continuing a packet:
> +				 * Move data into the saved SKB.
> +				 */
> +				skb_copy_to_linear_data_offset(priv->rx_1st_skb,
> +							       priv->rx_1st_skb->len,
> +							       skb->data,
> +							       desc_len);
> +				skb_put(priv->rx_1st_skb, desc_len);
> +				dev_kfree_skb(skb);
> +
> +				/* Set skb to point at the whole packet so that

   Please call it consistently, either SKB or skb (I prefer this one).

> +				 * we only need one code path for finishing a
> +				 * packet.
> +				 */
> +				skb = priv->rx_1st_skb;
> +			}
> +
> +			switch (die_dt) {
> +			case DT_FSINGLE:
> +			case DT_FEND:
> +				/* Finishing a packet:
> +				 * Determine protocol & checksum, hand off to
> +				 * NAPI and update our stats.
> +				 */
>  				skb->protocol = eth_type_trans(skb, ndev);
>  				if (ndev->features & NETIF_F_RXCSUM)
>  					ravb_rx_csum_gbeth(skb);
> +				stats->rx_bytes += skb->len;
>  				napi_gro_receive(&priv->napi[q], skb);
>  				rx_packets++;

   Otherwise, this is very good patch! Sorry for letting in the duplcate
code earlier! :-)

[...]

MBR, Sergey