netdev - [PATCH] net/mlx5e: parameter to disable symmetric hash

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Date:   Wed, 14 Dec 2022 17:35:42 +0300
From:   Alexandra Kossovsky <Alexandra.Kossovsky@...etlabs.ru>
To:     Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Maxim Mikityanskiy <maximmi@...dia.com>, netdev@...r.kernel.org
Subject: [PATCH] net/mlx5e: parameter to disable symmetric hash

Some AF_XDP applications assume standard Topelitz hash when spreading
traffic accross queues via RSS.  MLX5 driver always set "symmetric"
bit, which results in unexpected queues for any particular connection.

With this patch is is possible to disable that symmetric bit via
use_symmetric_hash module parameter, and use the standard Toeplitz hash
with well-known predictable result, same as for other NICs.

Signed-off-by: Alexandra N. Kossovsky <alexandra.kossovsky@...etlabs.ru>
---
 drivers/net/ethernet/mellanox/mlx5/core/en/tir.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/tir.c b/drivers/net/ethernet/mellanox/mlx5/core/en/tir.c
index d4239e3b3c88..63fb2608c0b0 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/tir.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/tir.c
@@ -5,6 +5,10 @@
 #include "params.h"
 #include <linux/mlx5/transobj.h>
 
+static bool use_symmetric_hash = true;
+module_param_named(use_symmetric_hash, use_symmetric_hash, bool, 0644);
+MODULE_PARM_DESC(use_symmetric_hash, "Use symmetric Toeplitz hash for RSS.");
+
 #define MLX5E_PARAMS_DEFAULT_LRO_WQE_SZ (64 * 1024)
 
 /* max() doesn't work inside square brackets. */
@@ -121,7 +125,8 @@ void mlx5e_tir_builder_build_rss(struct mlx5e_tir_builder *builder,
 		const size_t len = MLX5_FLD_SZ_BYTES(tirc, rx_hash_toeplitz_key);
 		void *rss_key = MLX5_ADDR_OF(tirc, tirc, rx_hash_toeplitz_key);
 
-		MLX5_SET(tirc, tirc, rx_hash_symmetric, 1);
+		if (use_symmetric_hash)
+			MLX5_SET(tirc, tirc, rx_hash_symmetric, 1);
 		memcpy(rss_key, rss_hash->toeplitz_hash_key, len);
 	}
 
-- 
2.30.2


-- 
Alexandra N. Kossovsky
OKTET Labs (http://www.oktetlabs.ru/)