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

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Date:   Thu, 1 Apr 2021 09:40:54 -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 1:57 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
>
> Rely on netif_receive_skb_list routine to send skbs converted from
> xdp_frames in cpu_map_kthread_run in order to improve i-cache usage.
> The proposed patch has been tested running xdp_redirect_cpu bpf sample
> available in the kernel tree that is used to redirect UDP frames from
> ixgbe driver to a cpumap entry and then to the networking stack.
> UDP frames are generated using pkt_gen.
>
> $xdp_redirect_cpu  --cpu <cpu> --progname xdp_cpu_map0 --dev <eth>
>
> bpf-next: ~2.2Mpps
> bpf-next + cpumap skb-list: ~3.15Mpps
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  kernel/bpf/cpumap.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index 0cf2791d5099..b33114ce2e2b 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -257,6 +257,7 @@ static int cpu_map_kthread_run(void *data)
>                 void *frames[CPUMAP_BATCH];
>                 void *skbs[CPUMAP_BATCH];
>                 int i, n, m, nframes;
> +               LIST_HEAD(list);
>
>                 /* Release CPU reschedule checks */
>                 if (__ptr_ring_empty(rcpu->queue)) {
> @@ -305,7 +306,6 @@ static int cpu_map_kthread_run(void *data)
>                 for (i = 0; i < nframes; i++) {
>                         struct xdp_frame *xdpf = frames[i];
>                         struct sk_buff *skb = skbs[i];
> -                       int ret;
>
>                         skb = __xdp_build_skb_from_frame(xdpf, skb,
>                                                          xdpf->dev_rx);
> @@ -314,11 +314,10 @@ static int cpu_map_kthread_run(void *data)
>                                 continue;
>                         }
>
> -                       /* 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

> +                       list_add_tail(&skb->list, &list);
>                 }
> +               netif_receive_skb_list(&list);
> +
>                 /* Feedback loop via tracepoint */
>                 trace_xdp_cpumap_kthread(rcpu->map_id, n, drops, sched, &stats);
>
> --
> 2.30.2
>