netdev - Re: [PATCH RFC v2 19/33] nfp: add XDP frame size to netronome driver

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Message-ID: <20200408105344.11d1a33f@kicinski-fedora-PC1C0HJN>
Date:   Wed, 8 Apr 2020 10:53:44 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     sameehj@...zon.com, netdev@...r.kernel.org, bpf@...r.kernel.org,
        zorik@...zon.com, akiyano@...zon.com, gtzalik@...zon.com,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        David Ahern <dsahern@...il.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [PATCH RFC v2 19/33] nfp: add XDP frame size to netronome
 driver

On Wed, 08 Apr 2020 13:52:10 +0200 Jesper Dangaard Brouer wrote:
> The netronome nfp driver already had a true_bufsz variable
> that contains what was needed for xdp.frame_sz.
> 
> Cc: Jakub Kicinski <kuba@...nel.org>
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
>  .../net/ethernet/netronome/nfp/nfp_net_common.c    |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> index 9bfb3b077bc1..b9b8c30eab33 100644
> --- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> +++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
> @@ -1817,6 +1817,7 @@ static int nfp_net_rx(struct nfp_net_rx_ring *rx_ring, int budget)
>  	rcu_read_lock();
>  	xdp_prog = READ_ONCE(dp->xdp_prog);
>  	true_bufsz = xdp_prog ? PAGE_SIZE : dp->fl_bufsz;
> +	xdp.frame_sz = true_bufsz;

Since this matters only with XDP on - we can set to PAGE_SIZE directly?

But more importantly the correct value is:

	PAGE_SIZE - NFP_NET_RX_BUF_HEADROOM

as we set hard_start at an offset. 

	xdp.data_hard_start = rxbuf->frag + NFP_NET_RX_BUF_HEADROOM;

Cause NFP_NET_RX_BUF_HEADROOM is not DMA mapped.

>  	xdp.rxq = &rx_ring->xdp_rxq;
>  	tx_ring = r_vec->xdp_ring;