netdev - Re: [PATCH bpf-next 10/11] i40e: implement AF

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Date:   Tue, 5 Jun 2018 15:07:52 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        "Duyck, Alexander H" <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>,
        MykytaI Iziumtsev <mykyta.iziumtsev@...aro.org>,
        John Fastabend <john.fastabend@...il.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        michael.lundkvist@...csson.com,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>,
        Francois Ozog <francois.ozog@...aro.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Brian Brooks <brian.brooks@...aro.org>,
        Andy Gospodarek <andy@...yhouse.net>,
        michael.chan@...adcom.com,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>
Subject: Re: [PATCH bpf-next 10/11] i40e: implement AF_XDP zero-copy support
 for Tx

Den tis 5 juni 2018 kl 14:44 skrev Jesper Dangaard Brouer <brouer@...hat.com>:
>
> On Mon,  4 Jun 2018 14:06:00 +0200
> Björn Töpel <bjorn.topel@...il.com> wrote:
>
> > Here, ndo_xsk_async_xmit is implemented. As a shortcut, the existing
> > XDP Tx rings are used for zero-copy. This will result in other devices
> > doing XDP_REDIRECT to an AF_XDP enabled queue will have its packets
> > dropped.
>
> This behavior is problematic, because XDP Tx rings are smp_processor_id
> based, and several RX queues can (via proc smp_affinity settings) be
> assigned to the same CPU. Thus, other RX-queues (than the AF_XDP
> enabled queue) can experience packet drops.  And other devices doing
> redirect through i40e, which happen to run on a CPU which XDP Tx queue
> is "hijacked" will see dropped packets.
>
> Any plans to allocate/create a dedicated TX ring per AF_XDP socket?
>

Yes -- again this was a shortcut, and must be addressed (for all the
reasons above).

Björn

> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer