netdev - [PATCH net-next 01/12] net/mlx5e: Use dma_rmb rather than rmb in CQE fetch routine

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Date:   Sat, 25 Mar 2017 00:52:03 +0300
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, kernel-team@...com,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: [PATCH net-next 01/12] net/mlx5e: Use dma_rmb rather than rmb in CQE fetch routine

Use dma_rmb in mlx5e_get_cqe rather than aggressive rmb (at least on
some architectures), this should help improve the performance on such
CPU archs where dma_rmb is optimized.

Performance improvement:
System: Intel(R) Xeon(R) CPU E5-2620 v3 @ 2.40GHz

Test case                   Baseline      Now      improvement
---------------------------------------------------------------
TX packets (24 threads)     45Mpps        50Mpps      11%
TC stack Drop (1 core)      3.45Mpps      3.6Mpps     5%
XDP Drop      (1 core)      14Mpps        16.9Mpps    20%
XDP TX        (1 core)      10.4Mpps      12Mpps      15%

Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
Reviewed-by: Tariq Toukan <tariqt@...lanox.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
index e5c12a732aa1..d8cda2f6239b 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c
@@ -44,7 +44,7 @@ struct mlx5_cqe64 *mlx5e_get_cqe(struct mlx5e_cq *cq)
 		return NULL;
 
 	/* ensure cqe content is read after cqe ownership bit */
-	rmb();
+	dma_rmb();
 
 	return cqe;
 }
-- 
2.11.0