Re: [dpdk-dev] [PATCH 1/3] net/bnx2x: fix to use required mem barriers in Rx path

[Jerin Jacob <jerinjacobk@gmail.com>]

+ Gavin

On Tue, Jan 14, 2020 at 6:09 AM Rasesh Mody <rmody@marvell.com> wrote:
>
> When handling RX completion queue PMD is not using required read/write
> barriers before reading completion queue element (CQE) indices,
> updating/writing hardware consumer and producer.
> This patch adds appropriate read/write memory barriers in places which
> are required by driver and adapter to read or update indices.
>
> Fixes: 540a211084a7 ("bnx2x: driver core")
> Cc: stable@dpdk.org
>
> Signed-off-by: Rasesh Mody <rmody@marvell.com>
> ---
>  drivers/net/bnx2x/bnx2x.c      |  5 +++++
>  drivers/net/bnx2x/bnx2x_rxtx.c | 22 ++++++++++++++++++++++
>  2 files changed, 27 insertions(+)
>
> diff --git a/drivers/net/bnx2x/bnx2x.c b/drivers/net/bnx2x/bnx2x.c
> index ed31335ac..9c5e7995d 100644
> --- a/drivers/net/bnx2x/bnx2x.c
> +++ b/drivers/net/bnx2x/bnx2x.c
> @@ -1255,6 +1255,11 @@ static uint8_t bnx2x_rxeof(struct bnx2x_softc *sc, struct bnx2x_fastpath *fp)
>                 return 0;
>         }
>
> +       /* Add memory barrier as status block fields can change. This memory
> +        * barrier will flush out all the read/write operations to status block
> +        * generated before the barrier. It will ensure stale data is not read
> +        */
> +       mb();

# Do you need full barriers here?
# Which architecture did you saw this issue?
# rte_cio_* barriers are performance Friday, Have you checked
rte_cio_* would suffice the requirements.
See the discussion in  http://patches.dpdk.org/patch/64038/

I assume 2/3 and 3/3 patches are for the slow path. if so, it is fine
to use full barriers on those patches.