netdev - Re: [bpf-next PATCH] xdp: accept that XDP headroom isn't always equal XDP_PACKET

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Date:   Tue, 03 Mar 2020 13:12:09 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>, bpf@...r.kernel.org
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>, gamemann@...clan.com,
        lrizzo@...gle.com, netdev@...r.kernel.org,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: Re: [bpf-next PATCH] xdp: accept that XDP headroom isn't always equal XDP_PACKET_HEADROOM

Jesper Dangaard Brouer <brouer@...hat.com> writes:

> The Intel based drivers (ixgbe + i40e) have implemented XDP with
> headroom 192 bytes and not the recommended 256 bytes defined by
> XDP_PACKET_HEADROOM.  For generic-XDP, accept that this headroom
> is also a valid size.
>
> Still for generic-XDP if headroom is less, still expand headroom to
> XDP_PACKET_HEADROOM as this is the default in most XDP drivers.
>
> Tested on ixgbe with xdp_rxq_info --skb-mode and --action XDP_DROP:
> - Before: 4,816,430 pps
> - After : 7,749,678 pps
> (Note that ixgbe in native mode XDP_DROP 14,704,539 pps)
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
> ---
>  include/uapi/linux/bpf.h |    1 +
>  net/core/dev.c           |    4 ++--
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 906e9f2752db..14dc4f9fb3c8 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3312,6 +3312,7 @@ struct bpf_xdp_sock {
>  };
>  
>  #define XDP_PACKET_HEADROOM 256
> +#define XDP_PACKET_HEADROOM_MIN 192

Do we need a comment here explaining why there are two values?

-Toke