On Thu, Nov 19, 2020 at 9:33 AM Björn Töpel <bjorn.topel@xxxxxxxxx> wrote:
>
> From: Björn Töpel <bjorn.topel@xxxxxxxxx>
>
> Add a check for need wake up in sendmsg(), so that if a user calls
> sendmsg() when no wakeup is needed, do not trigger a wakeup.
>
> To simplify the need wakeup check in the syscall, unconditionally
> enable the need wakeup flag for Tx. This has a side-effect for poll();
> If poll() is called for a socket without enabled need wakeup, a Tx
> wakeup is unconditionally performed.
>
> The wakeup matrix for AF_XDP now looks like:
>
> need wakeup | poll() | sendmsg() | recvmsg()
> ------------+--------------+-------------+------------
> disabled | wake Tx | wake Tx | nop
> enabled | check flag; | check flag; | check flag;
> | wake Tx/Rx | wake Tx | wake Rx
>
> Signed-off-by: Björn Töpel <bjorn.topel@xxxxxxxxx>
> ---
> net/xdp/xsk.c | 6 +++++-
> net/xdp/xsk_buff_pool.c | 13 ++++++-------
> 2 files changed, 11 insertions(+), 8 deletions(-)
Acked-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 56a52ec75696..bf0f5c34af6c 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -522,13 +522,17 @@ static int xsk_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len)
> bool need_wait = !(m->msg_flags & MSG_DONTWAIT);
> struct sock *sk = sock->sk;
> struct xdp_sock *xs = xdp_sk(sk);
> + struct xsk_buff_pool *pool;
>
> if (unlikely(!xsk_is_bound(xs)))
> return -ENXIO;
> if (unlikely(need_wait))
> return -EOPNOTSUPP;
>
> - return __xsk_sendmsg(sk);
> + pool = xs->pool;
> + if (pool->cached_need_wakeup & XDP_WAKEUP_TX)
> + return __xsk_sendmsg(sk);
> + return 0;
> }
>
> static int xsk_recvmsg(struct socket *sock, struct msghdr *m, size_t len, int flags)
> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index 8a3bf4e1318e..96bb607853ad 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -144,14 +144,13 @@ static int __xp_assign_dev(struct xsk_buff_pool *pool,
> if (err)
> return err;
>
> - if (flags & XDP_USE_NEED_WAKEUP) {
> + if (flags & XDP_USE_NEED_WAKEUP)
> pool->uses_need_wakeup = true;
> - /* Tx needs to be explicitly woken up the first time.
> - * Also for supporting drivers that do not implement this
> - * feature. They will always have to call sendto().
> - */
> - pool->cached_need_wakeup = XDP_WAKEUP_TX;
> - }
> + /* Tx needs to be explicitly woken up the first time. Also
> + * for supporting drivers that do not implement this
> + * feature. They will always have to call sendto() or poll().
> + */
> + pool->cached_need_wakeup = XDP_WAKEUP_TX;
>
> dev_hold(netdev);
>
> --
> 2.27.0
>
