netdev - Re: [PATCH bpf-next] cpumap: bulk skb using netif_receive_skb

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Date:   Thu, 1 Apr 2021 13:26:08 -0700
From:   Song Liu <song@...nel.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        lorenzo.bianconi@...hat.com,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH bpf-next] cpumap: bulk skb using netif_receive_skb_list

On Thu, Apr 1, 2021 at 9:49 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
>
> > On Thu, Apr 1, 2021 at 1:57 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> > >
>
> [...]
>
> > > -                       /* Inject into network stack */
> > > -                       ret = netif_receive_skb_core(skb);
> > > -                       if (ret == NET_RX_DROP)
> > > -                               drops++;
> >
> > I guess we stop tracking "drops" with this patch?
> >
> > Thanks,
> > Song
>
> Hi Song,
>
> we do not report the packets dropped by the stack but we still count the drops
> in the cpumap. If you think they are really important I guess we can change
> return value of netif_receive_skb_list returning the dropped packets or
> similar. What do you think?

I think we shouldn't silently change the behavior of the tracepoint below:

trace_xdp_cpumap_kthread(rcpu->map_id, n, drops, sched, &stats);

Returning dropped packets from netif_receive_skb_list() sounds good to me.

Thanks,
Song