netdev - Re: [PATCH v3 net-next 7/8] net: mvneta: make tx buffer array agnostic

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Date:   Tue, 15 Oct 2019 17:03:53 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     netdev@...r.kernel.org, lorenzo.bianconi@...hat.com,
        davem@...emloft.net, thomas.petazzoni@...tlin.com,
        brouer@...hat.com, ilias.apalodimas@...aro.org,
        matteo.croce@...hat.com, mw@...ihalf.com
Subject: Re: [PATCH v3 net-next 7/8] net: mvneta: make tx buffer array
 agnostic

On Mon, 14 Oct 2019 12:49:54 +0200, Lorenzo Bianconi wrote:
> Allow tx buffer array to contain both skb and xdp buffers in order to
> enable xdp frame recycling adding XDP_TX verdict support
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  drivers/net/ethernet/marvell/mvneta.c | 66 +++++++++++++++++----------
>  1 file changed, 43 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> index a79d81c9be7a..477ae6592fa3 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> @@ -561,6 +561,20 @@ struct mvneta_rx_desc {
>  };
>  #endif
>  
> +enum mvneta_tx_buf_type {
> +	MVNETA_TYPE_SKB,
> +	MVNETA_TYPE_XDP_TX,
> +	MVNETA_TYPE_XDP_NDO,
> +};
> +
> +struct mvneta_tx_buf {
> +	enum mvneta_tx_buf_type type;

I'd be tempted to try to encode type on the low bits of the pointer,
otherwise you're increasing the cache pressure here. I'm not 100% sure
it's worth the hassle, perhaps could be a future optimization.

> +	union {
> +		struct xdp_frame *xdpf;
> +		struct sk_buff *skb;
> +	};
> +};