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From:   =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn.topel@gmail.com>
Date:   Thu, 22 Aug 2019 09:10:58 +0200
Message-ID: <CAJ+HfNgUe3xGHeLsK0eKV76BOgeV-ZFcNwWKOvxbzcGRcg58dg@mail.gmail.com>
Subject: Re: [Intel-wired-lan] [PATCH net] ixgbe: fix double clean of tx
 descriptors with xdp
To:     Ilya Maximets <i.maximets@samsung.com>
Cc:     Alexander Duyck <alexander.duyck@gmail.com>,
        =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn.topel@intel.com>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Netdev <netdev@vger.kernel.org>, William Tu <u9012063@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        intel-wired-lan <intel-wired-lan@lists.osuosl.org>,
        bpf <bpf@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Magnus Karlsson <magnus.karlsson@intel.com>,
        Eelco Chaudron <echaudro@redhat.com>
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On Wed, 21 Aug 2019 at 18:22, Ilya Maximets <i.maximets@samsung.com> wrote:
>
> On 21.08.2019 4:17, Alexander Duyck wrote:
> > On Tue, Aug 20, 2019 at 8:58 AM Ilya Maximets <i.maximets@samsung.com> =
wrote:
> >>
> >> On 20.08.2019 18:35, Alexander Duyck wrote:
[...]
> >
> > So is it always in the same NAPI context?. I forgot, I was thinking
> > that somehow the socket could possibly make use of XDP for transmit.
>
> AF_XDP socket only triggers tx interrupt on ndo_xsk_async_xmit() which
> is used in zero-copy mode. Real xmit happens inside
> ixgbe_poll()
>  -> ixgbe_clean_xdp_tx_irq()
>     -> ixgbe_xmit_zc()
>
> This should be not possible to bound another XDP socket to the same netde=
v
> queue.
>
> It also possible to xmit frames in xdp_ring while performing XDP_TX/REDIR=
ECT
> actions. REDIRECT could happen from different netdev with different NAPI
> context, but this operation is bound to specific CPU core and each core h=
as
> its own xdp_ring.
>
> However, I'm not an expert here.
> Bj=C3=B6rn, maybe you could comment on this?
>

Yes, you're correct Ilya.