netdev - Re: [PATCH bpf-next 2/4] xsk: allow AF_XDP sockets to receive packets directly from a queue

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Date:   Tue, 8 Oct 2019 18:20:15 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Sridhar Samudrala <sridhar.samudrala@...el.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        maciej.fijalkowski@...el.com, tom.herbert@...el.com
Subject: Re: [PATCH bpf-next 2/4] xsk: allow AF_XDP sockets to receive packets
 directly from a queue

On Mon, Oct 7, 2019 at 11:18 PM Sridhar Samudrala
<sridhar.samudrala@...el.com> wrote:
> +
> +u32 bpf_direct_xsk(const struct bpf_prog *prog, struct xdp_buff *xdp)
> +{
> +       struct xdp_sock *xsk;
> +
> +       xsk = xdp_get_xsk_from_qid(xdp->rxq->dev, xdp->rxq->queue_index);
> +       if (xsk) {
> +               struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> +
> +               ri->xsk = xsk;
> +               return XDP_REDIRECT;
> +       }
> +
> +       return XDP_PASS;
> +}
> +EXPORT_SYMBOL(bpf_direct_xsk);

So you're saying there is a:
"""
xdpsock rxdrop 1 core (both app and queue's irq pinned to the same core)
   default : taskset -c 1 ./xdpsock -i enp66s0f0 -r -q 1
   direct-xsk :taskset -c 1 ./xdpsock -i enp66s0f0 -r -q 1
6.1x improvement in drop rate
"""

6.1x gain running above C code vs exactly equivalent BPF code?
How is that possible?