Re: [PATCH bpf-next v3 05/10] xsk: add busy-poll support for {recv,send}msg()

[Magnus Karlsson <magnus.karlsson@gmail.com>]

On Thu, Nov 19, 2020 at 9:33 AM Björn Töpel <bjorn.topel@gmail.com> wrote:
>
> From: Björn Töpel <bjorn.topel@intel.com>
>
> Wire-up XDP socket busy-poll support for recvmsg() and sendmsg(). If
> the XDP socket prefers busy-polling, make sure that no wakeup/IPI is
> performed.
>
> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
> ---
>  net/xdp/xsk.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)

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

> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index bf0f5c34af6c..ecc4579e41ee 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -23,6 +23,7 @@
>  #include <linux/netdevice.h>
>  #include <linux/rculist.h>
>  #include <net/xdp_sock_drv.h>
> +#include <net/busy_poll.h>
>  #include <net/xdp.h>
>
>  #include "xsk_queue.h"
> @@ -517,6 +518,17 @@ static int __xsk_sendmsg(struct sock *sk)
>         return xs->zc ? xsk_zc_xmit(xs) : xsk_generic_xmit(sk);
>  }
>
> +static bool xsk_no_wakeup(struct sock *sk)
> +{
> +#ifdef CONFIG_NET_RX_BUSY_POLL
> +       /* Prefer busy-polling, skip the wakeup. */
> +       return READ_ONCE(sk->sk_prefer_busy_poll) && READ_ONCE(sk->sk_ll_usec) &&
> +               READ_ONCE(sk->sk_napi_id) >= MIN_NAPI_ID;
> +#else
> +       return false;
> +#endif
> +}
> +
>  static int xsk_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
>  {
>         bool need_wait = !(m->msg_flags & MSG_DONTWAIT);
> @@ -529,6 +541,12 @@ static int xsk_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
>         if (unlikely(need_wait))
>                 return -EOPNOTSUPP;
>
> +       if (sk_can_busy_loop(sk))
> +               sk_busy_loop(sk, 1); /* only support non-blocking sockets */
> +
> +       if (xsk_no_wakeup(sk))
> +               return 0;
> +
>         pool = xs->pool;
>         if (pool->cached_need_wakeup & XDP_WAKEUP_TX)
>                 return __xsk_sendmsg(sk);
> @@ -550,6 +568,12 @@ static int xsk_recvmsg(struct socket *sock, struct msghdr *m, size_t len, int fl
>         if (unlikely(need_wait))
>                 return -EOPNOTSUPP;
>
> +       if (sk_can_busy_loop(sk))
> +               sk_busy_loop(sk, 1); /* only support non-blocking sockets */
> +
> +       if (xsk_no_wakeup(sk))
> +               return 0;
> +
>         if (xs->pool->cached_need_wakeup & XDP_WAKEUP_RX && xs->zc)
>                 return xsk_wakeup(xs, XDP_WAKEUP_RX);
>         return 0;
> --
> 2.27.0
>