Subject: Re: [net-next v2 9/9] ice: allow 3k MTU for XDP

From: Jesper Dangaard Brouer <[email-masked]>
Date: Tue, 5 Nov 2019 13:37:23 +0100

On Mon,  4 Nov 2019 13:51:25 -0800
Jeff Kirsher <[email-masked]> wrote:

> From: Maciej Fijalkowski <[email-masked]>
> 
> At this point ice driver is able to work on order 1 pages that are split
> onto two 3k buffers. Let's reflect that when user is setting new MTU
> size and XDP is present on interface.
> 
> Signed-off-by: Maciej Fijalkowski <[email-masked]>
> Signed-off-by: Tony Nguyen <[email-masked]>
> Tested-by: Andrew Bowers <[email-masked]>
> Signed-off-by: Jeff Kirsher <[email-masked]>
> ---
>  drivers/net/ethernet/intel/ice/ice_main.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
> index 29eea08807fd..363b284e8aa1 100644
> --- a/drivers/net/ethernet/intel/ice/ice_main.c
> +++ b/drivers/net/ethernet/intel/ice/ice_main.c
> @@ -4658,6 +4658,18 @@ static void ice_rebuild(struct ice_pf *pf, enum ice_reset_req reset_type)
>  	dev_err(dev, "Rebuild failed, unload and reload driver\n");
>  }
>  
> +/**
> + * ice_max_xdp_frame_size - returns the maximum allowed frame size for XDP
> + * @vsi: Pointer to VSI structure
> + */
> +static int ice_max_xdp_frame_size(struct ice_vsi *vsi)
> +{
> +	if (PAGE_SIZE >= 8192 || test_bit(ICE_FLAG_LEGACY_RX, vsi->back->flags))
> +		return ICE_RXBUF_2048 - XDP_PACKET_HEADROOM;

I've not checked the details of the ICE drivers memory model, are you
using a split-page model?

If so, in case of ICE_FLAG_LEGACY_RX and PAGE_SIZE==4096, then other
Intel drivers use headroom size 192 bytes and not
XDP_PACKET_HEADROOM=256, because it doesn't fit with split-page model.

Asked in another way: Have you taking into account the 320 bytes needed
by skb_shared_info ?

> +	else
> +		return ICE_RXBUF_3072;
> +}
> +
>  /**
>   * ice_change_mtu - NDO callback to change the MTU
>   * @netdev: network interface device structure
> @@ -4678,11 +4690,11 @@ static int ice_change_mtu(struct net_device *netdev, int new_mtu)
>  	}
>  
>  	if (ice_is_xdp_ena_vsi(vsi)) {
> -		int frame_size = ICE_RXBUF_2048 - XDP_PACKET_HEADROOM;
> +		int frame_size = ice_max_xdp_frame_size(vsi);
>  
>  		if (new_mtu + ICE_ETH_PKT_HDR_PAD > frame_size) {
>  			netdev_err(netdev, "max MTU for XDP usage is %d\n",
> -				   frame_size);
> +				   frame_size - ICE_ETH_PKT_HDR_PAD);
>  			return -EINVAL;
>  		}
>  	}

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer