netdev - Re: [PATCH bpf-next 07/15] xsk: add Rx receive functions and poll support

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Message-ID: <CAF=yD-LAqKaC5U1ZR7ZNyZpmBonp9W68qp8z3v-P8cKFkXe4AA@mail.gmail.com>
Date:   Tue, 24 Apr 2018 12:56:28 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Alexander Duyck <alexander.h.duyck@...el.com>,
        Alexander Duyck <alexander.duyck@...il.com>,
        John Fastabend <john.fastabend@...il.com>,
        Alexei Starovoitov <ast@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Network Development <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        michael.lundkvist@...csson.com,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Singhai, Anjali" <anjali.singhai@...el.com>,
        "Zhang, Qi Z" <qi.z.zhang@...el.com>
Subject: Re: [PATCH bpf-next 07/15] xsk: add Rx receive functions and poll support

On Mon, Apr 23, 2018 at 9:56 AM, Björn Töpel <bjorn.topel@...il.com> wrote:
> From: Björn Töpel <bjorn.topel@...el.com>
>
> Here the actual receive functions of AF_XDP are implemented, that in a
> later commit, will be called from the XDP layers.
>
> There's one set of functions for the XDP_DRV side and another for
> XDP_SKB (generic).
>
> Support for the poll syscall is also implemented.
>
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> ---

> +/* Common functions operating for both RXTX and umem queues */
> +
> +static inline u32 xskq_nb_avail(struct xsk_queue *q, u32 dcnt)
> +{
> +       u32 entries = q->prod_tail - q->cons_tail;
> +
> +       if (entries == 0) {
> +               /* Refresh the local pointer */
> +               q->prod_tail = READ_ONCE(q->ring->producer);
> +       }
> +
> +       entries = q->prod_tail - q->cons_tail;

Probably meant to be inside the branch? Though I see the same
pattern in the userspace example program.

> +static inline u32 *xskq_validate_id(struct xsk_queue *q)
> +{
> +       while (q->cons_tail != q->cons_head) {
> +               struct xdp_umem_ring *ring = (struct xdp_umem_ring *)q->ring;
> +               unsigned int idx = q->cons_tail & q->ring_mask;
> +
> +               if (xskq_is_valid_id(q, ring->desc[idx]))
> +                       return &ring->desc[idx];

Missing a q->cons_tail increment in this loop?