linux-kernel - Re: [PATCH net-next] net: lantiq

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Date:   Wed, 13 Jul 2022 14:50:48 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Aleksander Jan Bajkowski <olek2@...pl>
Cc:     hauke@...ke-m.de, David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: lantiq_xrx200: use skb cache

On Tue, Jul 12, 2022 at 8:15 PM Aleksander Jan Bajkowski <olek2@...pl> wrote:
>
> napi_build_skb() reuses NAPI skbuff_head cache in order to save some
> cycles on freeing/allocating skbuff_heads on every new Rx or completed
> Tx.
> Use napi_consume_skb() to feed the cache with skbuff_heads of completed
> Tx. The budget parameter is added to indicate NAPI context, as a value
> of zero can be passed in the case of netpoll.
>
> NAT performance results on BT Home Hub 5A (kernel 5.15.45, mtu 1500):
>
> Fast path (Software Flow Offload):
>         Up      Down
> Before  702.4   719.3
> After   707.3   739.9
>
> Slow path:
>         Up      Down
> Before  91.8    184.1
> After   92.0    185.7
>
> Signed-off-by: Aleksander Jan Bajkowski <olek2@...pl>
> ---
>  drivers/net/ethernet/lantiq_xrx200.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/lantiq_xrx200.c b/drivers/net/ethernet/lantiq_xrx200.c
> index 5edb68a8aab1..83e07404803f 100644
> --- a/drivers/net/ethernet/lantiq_xrx200.c
> +++ b/drivers/net/ethernet/lantiq_xrx200.c
> @@ -238,7 +238,7 @@ static int xrx200_hw_receive(struct xrx200_chan *ch)
>                 return ret;
>         }
>
> -       skb = build_skb(buf, priv->rx_skb_size);
> +       skb = napi_build_skb(buf, priv->rx_skb_size);

If you are changing this code path, what about adding proper error recovery ?

skb can be NULL at this point :/


>         skb_reserve(skb, NET_SKB_PAD);
>         skb_put(skb, len);
>
> @@ -321,7 +321,7 @@ static int xrx200_tx_housekeeping(struct napi_struct *napi, int budget)
>                         pkts++;
>                         bytes += skb->len;
>                         ch->skb[ch->tx_free] = NULL;
> -                       consume_skb(skb);
> +                       napi_consume_skb(skb, budget);
>                         memset(&ch->dma.desc_base[ch->tx_free], 0,
>                                sizeof(struct ltq_dma_desc));
>                         ch->tx_free++;
> --
> 2.30.2
>