netdev - Re: [PATCH bpf] net: xsk: don't return frames via the allocator on error

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Date:   Mon, 30 Jul 2018 13:04:38 +0200
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        oss-drivers@...ronome.com, Netdev <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>
Subject: Re: [PATCH bpf] net: xsk: don't return frames via the allocator on error

Den lör 28 juli 2018 kl 05:21 skrev Jakub Kicinski
<jakub.kicinski@...ronome.com>:
>
> xdp_return_buff() is used when frame has been successfully
> handled (transmitted) or if an error occurred during delayed
> processing and there is no way to report it back to
> xdp_do_redirect().
>
> In case of __xsk_rcv_zc() error is propagated all the way
> back to the driver, so there is no need to call
> xdp_return_buff().  Driver will recycle the frame anyway
> after seeing that error happened.
>
> Fixes: 173d3adb6f43 ("xsk: add zero-copy support for Rx")
> Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
> ---
> Patch could as well be applied to bpf-next, since there are no drivers
> for AF_XDP in tree, yet.  xdp_umem_get_dma() and xdp_umem_get_data() are
> not even exported.  But one could reimplent those...
>
> As I mentioned I think this makes the entire MEM_TYPE_ZERO_COPY allocator
> handling dead code now :(
>

Nice Jakub!

Indeed, as you state, there's no ZC driver implementation yet. So,
either bpf or bpf-next.

Acked-by: Björn Töpel <bjorn.topel@...el.com>

>  net/xdp/xsk.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 72335c2e8108..4e937cd7c17d 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -84,10 +84,8 @@ static int __xsk_rcv_zc(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
>  {
>         int err = xskq_produce_batch_desc(xs->rx, (u64)xdp->handle, len);
>
> -       if (err) {
> -               xdp_return_buff(xdp);
> +       if (err)
>                 xs->rx_dropped++;
> -       }
>
>         return err;
>  }
> --
> 2.17.1
>