netdev - Re: [Intel-wired-lan] [PATCH net] ixgbe: fix double clean of tx descriptors with xdp

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Date:   Thu, 22 Aug 2019 09:10:58 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Ilya Maximets <i.maximets@...sung.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>, William Tu <u9012063@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        bpf <bpf@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Eelco Chaudron <echaudro@...hat.com>
Subject: Re: [Intel-wired-lan] [PATCH net] ixgbe: fix double clean of tx
 descriptors with xdp

On Wed, 21 Aug 2019 at 18:22, Ilya Maximets <i.maximets@...sung.com> wrote:
>
> On 21.08.2019 4:17, Alexander Duyck wrote:
> > On Tue, Aug 20, 2019 at 8:58 AM Ilya Maximets <i.maximets@...sung.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 netdev
> queue.
>
> It also possible to xmit frames in xdp_ring while performing XDP_TX/REDIRECT
> actions. REDIRECT could happen from different netdev with different NAPI
> context, but this operation is bound to specific CPU core and each core has
> its own xdp_ring.
>
> However, I'm not an expert here.
> Björn, maybe you could comment on this?
>

Yes, you're correct Ilya.