netdev - [PATCH net 1/7] mlxsw: spectrum: Use different seeds for ECMP and LAG hash

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Message-Id: <20190611071946.11089-2-idosch@idosch.org>
Date:   Tue, 11 Jun 2019 10:19:40 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, jiri@...lanox.com, petrm@...lanox.com,
        alexpe@...lanox.com, mlxsw@...lanox.com,
        Ido Schimmel <idosch@...lanox.com>
Subject: [PATCH net 1/7] mlxsw: spectrum: Use different seeds for ECMP and LAG hash

From: Ido Schimmel <idosch@...lanox.com>

The same hash function and seed are used for both ECMP and LAG hash.
Therefore, when a LAG device is used as a nexthop device as part of an
ECMP group, hash polarization can occur and all the traffic will be
hashed to a single LAG slave.

Fix this by using a different seed for the LAG hash.

Fixes: fa73989f2697 ("mlxsw: spectrum: Use a stable ECMP/LAG seed")
Signed-off-by: Ido Schimmel <idosch@...lanox.com>
Reported-by: Alex Veber <alexve@...lanox.com>
Tested-by: Alex Veber <alexve@...lanox.com>
Acked-by: Jiri Pirko <jiri@...lanox.com>
---
 drivers/net/ethernet/mellanox/mlxsw/spectrum.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum.c
index dfe6b44baf63..23204356ad88 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum.c
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum.c
@@ -4280,13 +4280,16 @@ static void mlxsw_sp_traps_fini(struct mlxsw_sp *mlxsw_sp)
 	}
 }
 
+#define MLXSW_SP_LAG_SEED_INIT 0xcafecafe
+
 static int mlxsw_sp_lag_init(struct mlxsw_sp *mlxsw_sp)
 {
 	char slcr_pl[MLXSW_REG_SLCR_LEN];
 	u32 seed;
 	int err;
 
-	seed = jhash(mlxsw_sp->base_mac, sizeof(mlxsw_sp->base_mac), 0);
+	seed = jhash(mlxsw_sp->base_mac, sizeof(mlxsw_sp->base_mac),
+		     MLXSW_SP_LAG_SEED_INIT);
 	mlxsw_reg_slcr_pack(slcr_pl, MLXSW_REG_SLCR_LAG_HASH_SMAC |
 				     MLXSW_REG_SLCR_LAG_HASH_DMAC |
 				     MLXSW_REG_SLCR_LAG_HASH_ETHERTYPE |
-- 
2.20.1