[dpdk-stable] [PATCH] net/i40e: fix out of order Rx read
Yuanhan Liu
yuanhan.liu at linux.intel.com
Wed Nov 9 05:54:13 CET 2016
Applied to dpdk-stable branch 16.07.
Thanks.
--yliu
On Mon, Nov 07, 2016 at 01:46:08AM +0800, Qi Zhang wrote:
> In vPMD, when we load Rx desc with _mm_loadu_si128, the volatile
> modifier will be cast away, allowing the compiler to reorder the
> load instructions.
>
> The Rx recv function's correctness is relying on these load
> instructions following a strict sequence, reading the descriptors
> in reverse order, so we add compiler barrier to prevent compiler
> reorder.
>
> Fixes: 9ed94e5bb04e ("i40e: add vector Rx")
>
> Signed-off-by: Qi Zhang <qi.z.zhang at intel.com>
> ---
> drivers/net/i40e/i40e_rxtx_vec.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/i40e/i40e_rxtx_vec.c b/drivers/net/i40e/i40e_rxtx_vec.c
> index 82571ee..a9649d3 100644
> --- a/drivers/net/i40e/i40e_rxtx_vec.c
> +++ b/drivers/net/i40e/i40e_rxtx_vec.c
> @@ -282,7 +282,7 @@ _recv_raw_pkts_vec(struct i40e_rx_queue *rxq, struct rte_mbuf **rx_pkts,
> /* Read desc statuses backwards to avoid race condition */
> /* A.1 load 4 pkts desc */
> descs[3] = _mm_loadu_si128((__m128i *)(rxdp + 3));
> -
> + rte_compiler_barrier();
> /* B.2 copy 2 mbuf point into rx_pkts */
> _mm_storeu_si128((__m128i *)&rx_pkts[pos], mbp1);
>
> @@ -290,8 +290,10 @@ _recv_raw_pkts_vec(struct i40e_rx_queue *rxq, struct rte_mbuf **rx_pkts,
> mbp2 = _mm_loadu_si128((__m128i *)&sw_ring[pos+2]);
>
> descs[2] = _mm_loadu_si128((__m128i *)(rxdp + 2));
> + rte_compiler_barrier();
> /* B.1 load 2 mbuf point */
> descs[1] = _mm_loadu_si128((__m128i *)(rxdp + 1));
> + rte_compiler_barrier();
> descs[0] = _mm_loadu_si128((__m128i *)(rxdp));
>
> /* B.2 copy 2 mbuf point into rx_pkts */
> --
> 2.7.4
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