netdev - Re: [PATCH bpf-next] samples/bpf: Attach XDP programs in driver mode by default

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Message-ID: <71b7ba89-7780-8ce1-1b30-67ae6ebc214c@gmail.com>
Date:   Mon, 16 Dec 2019 08:01:14 -0700
From:   David Ahern <dsahern@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH bpf-next] samples/bpf: Attach XDP programs in driver mode
 by default

On 12/16/19 4:07 AM, Toke Høiland-Jørgensen wrote:
> When attaching XDP programs, userspace can set flags to request the attach
> mode (generic/SKB mode, driver mode or hw offloaded mode). If no such flags
> are requested, the kernel will attempt to attach in driver mode, and then
> silently fall back to SKB mode if this fails.
> 
> The silent fallback is a major source of user confusion, as users will try
> to load a program on a device without XDP support, and instead of an error
> they will get the silent fallback behaviour, not notice, and then wonder
> why performance is not what they were expecting.
> 
> In an attempt to combat this, let's switch all the samples to default to
> explicitly requesting driver-mode attach. As part of this, ensure that all
> the userspace utilities have a switch to enable SKB mode. For those that
> have a switch to request driver mode, keep it but turn it into a no-op.
> 
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  samples/bpf/xdp1_user.c             |  5 ++++-
>  samples/bpf/xdp_adjust_tail_user.c  |  5 ++++-
>  samples/bpf/xdp_fwd_user.c          | 17 ++++++++++++++---
>  samples/bpf/xdp_redirect_cpu_user.c |  4 ++++
>  samples/bpf/xdp_redirect_map_user.c |  5 ++++-
>  samples/bpf/xdp_redirect_user.c     |  5 ++++-
>  samples/bpf/xdp_router_ipv4_user.c  |  3 +++
>  samples/bpf/xdp_rxq_info_user.c     |  4 ++++
>  samples/bpf/xdp_sample_pkts_user.c  | 12 +++++++++---
>  samples/bpf/xdp_tx_iptunnel_user.c  |  5 ++++-
>  samples/bpf/xdpsock_user.c          |  5 ++++-
>  11 files changed, 58 insertions(+), 12 deletions(-)
> 

Acked-by: David Ahern <dsahern@...il.com>

Thanks for doing this, Toke.