netdev - Re: [bpf-next PATCH 2/2] samples/bpf: xdp_rxq_info action XDP

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Message-ID: <CAPhsuW47P=FXFPoTMEFuKY9Sgz5N4w5sHDWaScaqCDnSqiCRQg@mail.gmail.com>
Date:   Wed, 27 Jun 2018 10:02:06 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Networking <netdev@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [bpf-next PATCH 2/2] samples/bpf: xdp_rxq_info action XDP_TX must
 adjust MAC-addrs

On Wed, Jun 27, 2018 at 4:20 AM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
> On Tue, 26 Jun 2018 17:09:01 -0700
> Song Liu <liu.song.a23@...il.com> wrote:
>
>> On Mon, Jun 25, 2018 at 7:27 AM, Jesper Dangaard Brouer
>> <brouer@...hat.com> wrote:
>> > XDP_TX requires also changing the MAC-addrs, else some hardware
>> > may drop the TX packet before reaching the wire.  This was
>> > observed with driver mlx5.
>> >
>> > If xdp_rxq_info select --action XDP_TX the swapmac functionality
>> > is activated.  It is also possible to manually enable via cmdline
>> > option --swapmac.  This is practical if wanting to measure the
>> > overhead of writing/updating payload for other action types.
>> >
>> > Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
>> > Signed-off-by: Toke Høiland-Jørgensen <toke@...e.dk>
>> > ---
> [...]
>> >
>> > diff --git a/samples/bpf/xdp_rxq_info_kern.c b/samples/bpf/xdp_rxq_info_kern.c
>> > index 61af6210df2f..222a83eed1cb 100644
>> > --- a/samples/bpf/xdp_rxq_info_kern.c
>> > +++ b/samples/bpf/xdp_rxq_info_kern.c
>> > @@ -21,6 +21,7 @@ struct config {
>> >  enum cfg_options_flags {
>> >         NO_TOUCH = 0x0U,
>> >         READ_MEM = 0x1U,
>> > +       SWAP_MAC = 0x2U,
>> >  };
> [...]
>> > @@ -98,7 +116,7 @@ int  xdp_prognum0(struct xdp_md *ctx)
>> >                 rxq_rec->issue++;
>> >
>> >         /* Default: Don't touch packet data, only count packets */
>> > -       if (unlikely(config->options & READ_MEM)) {
>> > +       if (unlikely(config->options & (READ_MEM|SWAP_MAC))) {
>> >                 struct ethhdr *eth = data;
>> >
>> >                 if (eth + 1 > data_end)
> [...]
>
>> > diff --git a/samples/bpf/xdp_rxq_info_user.c b/samples/bpf/xdp_rxq_info_user.c
>> > index 435485d4f49e..248a7eab9531 100644
> [...]
>> > @@ -119,6 +121,8 @@ static char* options2str(enum cfg_options_flags flag)
>> >  {
>> >         if (flag == NO_TOUCH)
>> >                 return "no_touch";
>> > +       if (flag & SWAP_MAC)
>> > +               return "swapmac";
>> >         if (flag & READ_MEM)
>> >                 return "read";
>>
>> I guess SWAP_MAC also reads the memory, so it "includes" READ_MEM?
>
> True (see _kern side)
>
>> It is OK for now. We may need to refactor this part when adding other
>> flags in the future.
>
> Sure, do remember that this is only a 'sample' program.

Agreed.

Acked-by: Song Liu <songliubraving@...com>