Re: [PATCH net-next] net: lantiq_xrx200: use skb cache

Eric Dumazet
2022-07-13T12:51:05Z

On Tue, Jul 12, 2022 at 8:15 PM Aleksander Jan Bajkowski <olek2@wp.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@wp.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
>