[Intel-wired-lan] [PATCH net-next 23/33] ixgbe: add XDP frame size to driver

[Daniel Borkmann]

On 4/22/20 6:09 PM, Jesper Dangaard Brouer wrote:
> This driver uses different memory models depending on PAGE_SIZE at
> compile time. For PAGE_SIZE 4K it uses page splitting, meaning for
> normal MTU frame size is 2048 bytes (and headroom 192 bytes). For
> larger MTUs the driver still use page splitting, by allocating
> order-1 pages (8192 bytes) for RX frames. For PAGE_SIZE larger than
> 4K, driver instead advance its rx_buffer->page_offset with the frame
> size "truesize".
> 
> For XDP frame size calculations, this mean that in PAGE_SIZE larger
> than 4K mode the frame_sz change on a per packet basis. For the page
> split 4K PAGE_SIZE mode, xdp.frame_sz is more constant and can be
> updated once outside the main NAPI loop.
> 
> The default setting in the driver uses build_skb(), which provides
> the necessary headroom and tailroom for XDP-redirect in RX-frame
> (in both modes).
> 
> There is one complication, which is legacy-rx mode (configurable via
> ethtool priv-flags). There are zero headroom in this mode, which is a
> requirement for XDP-redirect to work. The conversion to xdp_frame
> (convert_to_xdp_frame) will detect this insufficient space, and
> xdp_do_redirect() call will fail. This is deemed acceptable, as it
> allows other XDP actions to still work in legacy-mode. In
> legacy-mode + larger PAGE_SIZE due to lacking tailroom, we also
> accept that xdp_adjust_tail shrink doesn't work.
> 
> Cc: intel-wired-lan at lists.osuosl.org
> Cc: Jeff Kirsher <jeffrey.t.kirsher at intel.com>
> Cc: Alexander Duyck <alexander.duyck at gmail.com>
> Signed-off-by: Jesper Dangaard Brouer <brouer at redhat.com>

Alexander/Jeff, in case the ixgbe/i40e/ice changes look good to you,
please ack.

Thanks,
Daniel