netdev - Re: [PATCH bpf-next v3 08/10] samples/bpf: use recvfrom() in xdpsock/l2fwd

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Date:   Wed, 25 Nov 2020 09:00:43 +0100
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
        "Samudrala, Sridhar" <sridhar.samudrala@...el.com>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>
Subject: Re: [PATCH bpf-next v3 08/10] samples/bpf: use recvfrom() in xdpsock/l2fwd

On Thu, Nov 19, 2020 at 9:33 AM Björn Töpel <bjorn.topel@...il.com> wrote:
>
> From: Björn Töpel <bjorn.topel@...el.com>
>
> Start using recvfrom() the l2fwd scenario, instead of poll() which is
> more expensive and need additional knobs for busy-polling.
>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> ---
>  samples/bpf/xdpsock_user.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)

Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>

> diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
> index f90111b95b2e..24aa7511c4c8 100644
> --- a/samples/bpf/xdpsock_user.c
> +++ b/samples/bpf/xdpsock_user.c
> @@ -1098,8 +1098,7 @@ static void kick_tx(struct xsk_socket_info *xsk)
>         exit_with_error(errno);
>  }
>
> -static inline void complete_tx_l2fwd(struct xsk_socket_info *xsk,
> -                                    struct pollfd *fds)
> +static inline void complete_tx_l2fwd(struct xsk_socket_info *xsk)
>  {
>         struct xsk_umem_info *umem = xsk->umem;
>         u32 idx_cq = 0, idx_fq = 0;
> @@ -1134,7 +1133,7 @@ static inline void complete_tx_l2fwd(struct xsk_socket_info *xsk,
>                                 exit_with_error(-ret);
>                         if (xsk_ring_prod__needs_wakeup(&umem->fq)) {
>                                 xsk->app_stats.fill_fail_polls++;
> -                               ret = poll(fds, num_socks, opt_timeout);
> +                               recvfrom(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, NULL);
>                         }
>                         ret = xsk_ring_prod__reserve(&umem->fq, rcvd, &idx_fq);
>                 }
> @@ -1331,19 +1330,19 @@ static void tx_only_all(void)
>                 complete_tx_only_all();
>  }
>
> -static void l2fwd(struct xsk_socket_info *xsk, struct pollfd *fds)
> +static void l2fwd(struct xsk_socket_info *xsk)
>  {
>         unsigned int rcvd, i;
>         u32 idx_rx = 0, idx_tx = 0;
>         int ret;
>
> -       complete_tx_l2fwd(xsk, fds);
> +       complete_tx_l2fwd(xsk);
>
>         rcvd = xsk_ring_cons__peek(&xsk->rx, opt_batch_size, &idx_rx);
>         if (!rcvd) {
>                 if (xsk_ring_prod__needs_wakeup(&xsk->umem->fq)) {
>                         xsk->app_stats.rx_empty_polls++;
> -                       ret = poll(fds, num_socks, opt_timeout);
> +                       recvfrom(xsk_socket__fd(xsk->xsk), NULL, 0, MSG_DONTWAIT, NULL, NULL);
>                 }
>                 return;
>         }
> @@ -1353,7 +1352,7 @@ static void l2fwd(struct xsk_socket_info *xsk, struct pollfd *fds)
>         while (ret != rcvd) {
>                 if (ret < 0)
>                         exit_with_error(-ret);
> -               complete_tx_l2fwd(xsk, fds);
> +               complete_tx_l2fwd(xsk);
>                 if (xsk_ring_prod__needs_wakeup(&xsk->tx)) {
>                         xsk->app_stats.tx_wakeup_sendtos++;
>                         kick_tx(xsk);
> @@ -1388,22 +1387,20 @@ static void l2fwd_all(void)
>         struct pollfd fds[MAX_SOCKS] = {};
>         int i, ret;
>
> -       for (i = 0; i < num_socks; i++) {
> -               fds[i].fd = xsk_socket__fd(xsks[i]->xsk);
> -               fds[i].events = POLLOUT | POLLIN;
> -       }
> -
>         for (;;) {
>                 if (opt_poll) {
> -                       for (i = 0; i < num_socks; i++)
> +                       for (i = 0; i < num_socks; i++) {
> +                               fds[i].fd = xsk_socket__fd(xsks[i]->xsk);
> +                               fds[i].events = POLLOUT | POLLIN;
>                                 xsks[i]->app_stats.opt_polls++;
> +                       }
>                         ret = poll(fds, num_socks, opt_timeout);
>                         if (ret <= 0)
>                                 continue;
>                 }
>
>                 for (i = 0; i < num_socks; i++)
> -                       l2fwd(xsks[i], fds);
> +                       l2fwd(xsks[i]);
>
>                 if (benchmark_done)
>                         break;
> --
> 2.27.0
>