linux-kernel - RE: [PATCH net 2/3] net: enetc: refactor bulk flipping of RX buffers to separate function

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Message-ID:
 <PAXPR04MB851079583B566E942D4206EB88BF2@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Fri, 18 Apr 2025 07:44:06 +0000
From: Wei Fang <wei.fang@....com>
To: Vladimir Oltean <vladimir.oltean@....com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
CC: Claudiu Manoil <claudiu.manoil@....com>, Clark Wang
	<xiaoning.wang@....com>, Vlatko Markovikj <vlatko.markovikj@...s.com>, Andrew
 Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
	<daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>, John
 Fastabend <john.fastabend@...il.com>, Lorenzo Bianconi <lorenzo@...nel.org>,
	Toke Hoiland-Jorgensen <toke@...hat.com>, Alexander Lobakin
	<aleksander.lobakin@...el.com>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: RE: [PATCH net 2/3] net: enetc: refactor bulk flipping of RX buffers
 to separate function

> This small snippet of code ensures that we do something with the array
> of RX software buffer descriptor elements after passing the skb to the
> stack. In this case, we see if the other half of the page is reusable,
> and if so, we "turn around" the buffers, making them directly usable by
> enetc_refill_rx_ring() without going to enetc_new_page().
> 
> We will need to perform this kind of buffer flipping from a new code
> path, i.e. from XDP_PASS. Currently, enetc_build_skb() does it there
> buffer by buffer, but in a subsequent change we will stop using
> enetc_build_skb() for XDP_PASS.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
>  drivers/net/ethernet/freescale/enetc/enetc.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c
> b/drivers/net/ethernet/freescale/enetc/enetc.c
> index 9b333254c73e..74721995cb1f 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc.c
> @@ -1850,6 +1850,16 @@ static void enetc_xdp_drop(struct enetc_bdr *rx_ring,
> int rx_ring_first,
>  	}
>  }
> 
> +static void enetc_bulk_flip_buff(struct enetc_bdr *rx_ring, int rx_ring_first,
> +				 int rx_ring_last)
> +{
> +	while (rx_ring_first != rx_ring_last) {
> +		enetc_flip_rx_buff(rx_ring,
> +				   &rx_ring->rx_swbd[rx_ring_first]);
> +		enetc_bdr_idx_inc(rx_ring, &rx_ring_first);
> +	}
> +}
> +
>  static int enetc_clean_rx_ring_xdp(struct enetc_bdr *rx_ring,
>  				   struct napi_struct *napi, int work_limit,
>  				   struct bpf_prog *prog)
> @@ -1965,11 +1975,7 @@ static int enetc_clean_rx_ring_xdp(struct enetc_bdr
> *rx_ring,
>  				enetc_xdp_drop(rx_ring, orig_i, i);
>  				rx_ring->stats.xdp_redirect_failures++;
>  			} else {
> -				while (orig_i != i) {
> -					enetc_flip_rx_buff(rx_ring,
> -							   &rx_ring->rx_swbd[orig_i]);
> -					enetc_bdr_idx_inc(rx_ring, &orig_i);
> -				}
> +				enetc_bulk_flip_buff(rx_ring, orig_i, i);
>  				xdp_redirect_frm_cnt++;
>  				rx_ring->stats.xdp_redirect++;
>  			}
> --
> 2.34.1

Reviewed-by: Wei Fang <wei.fang@....com>