netdev - Re: [PATCH v14 bpf-next 03/18] net: mvneta: update mb bit before passing the xdp buffer to eBPF layer

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Date:   Mon, 20 Sep 2021 11:25:54 +0300
From:   Shay Agroskin <shayagr@...zon.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
CC:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>,
        <lorenzo.bianconi@...hat.com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <ast@...nel.org>, <daniel@...earbox.net>,
        <john.fastabend@...il.com>, <dsahern@...nel.org>,
        <brouer@...hat.com>, <echaudro@...hat.com>, <jasowang@...hat.com>,
        <alexander.duyck@...il.com>, <saeed@...nel.org>,
        <maciej.fijalkowski@...el.com>, <magnus.karlsson@...el.com>,
        <tirthendu.sarkar@...el.com>, <toke@...hat.com>
Subject: Re: [PATCH v14 bpf-next 03/18] net: mvneta: update mb bit before
 passing the xdp buffer to eBPF layer


Lorenzo Bianconi <lorenzo@...nel.org> writes:

> ...
> diff --git a/drivers/net/ethernet/marvell/mvneta.c 
> b/drivers/net/ethernet/marvell/mvneta.c
> index 9d460a270601..0c7b84ca6efc 100644
> --- a/drivers/net/ethernet/marvell/mvneta.c
> +++ b/drivers/net/ethernet/marvell/mvneta.c
> ...
> @@ -2320,8 +2325,12 @@ mvneta_swbm_build_skb(struct mvneta_port 
> *pp, struct page_pool *pool,
>  		      struct xdp_buff *xdp, u32 desc_status)
>  {
>  	struct skb_shared_info *sinfo = 
>  xdp_get_shared_info_from_buff(xdp);
> -	int i, num_frags = sinfo->nr_frags;
>  	struct sk_buff *skb;
> +	u8 num_frags;
> +	int i;
> +
> +	if (unlikely(xdp_buff_is_mb(xdp)))
> +		num_frags = sinfo->nr_frags;

Hi,
nit, it seems that the num_frags assignment can be moved after the 
other 'if' condition you added (right before the 'for' for 
num_frags), or even be eliminated completely so that 
sinfo->nr_frags is used directly.
Either way it looks like you can remove one 'if'.

Shay

>  
>  	skb = build_skb(xdp->data_hard_start, PAGE_SIZE);
>  	if (!skb)
> @@ -2333,6 +2342,9 @@ mvneta_swbm_build_skb(struct mvneta_port 
> *pp, struct page_pool *pool,
>  	skb_put(skb, xdp->data_end - xdp->data);
>  	skb->ip_summed = mvneta_rx_csum(pp, desc_status);
>  
> +	if (likely(!xdp_buff_is_mb(xdp)))
> +		goto out;
> +
>  	for (i = 0; i < num_frags; i++) {
>  		skb_frag_t *frag = &sinfo->frags[i];
>  
> @@ -2341,6 +2353,7 @@ mvneta_swbm_build_skb(struct mvneta_port 
> *pp, struct page_pool *pool,
>  				skb_frag_size(frag), PAGE_SIZE);
>  	}
>  
> +out:
>  	return skb;
>  }