On Mon, 25 Feb 2019 10:16:15 +0100, papito favaro wrote: > Hi all, > I woulld like to understand if the behaviour i'm getting is correct. > > When I configure the XDP_UMEM_REG in zerocopy mode with a headroom == > 0 on a i40e, > the driver (i guess) actually sets a headroom of 256. > if i set a headroom == 256 the driver sets a headroom of 512. > > If this behaviour is correct, would be nice that the xdp_umem_reg > struct after the setsockopt call would contain the actual configured > headroom. Kernel's XDP may require up to 256B (XDP_PACKET_HEADROOM) of headroom this is for calls to xdp_adjust_head() which may want to prepend data. The AF_XDP headroom is extra, beyond that. Perhaps we should document that as expected behaviour? (Does it hold for ixgbe?)
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