* [PATCH V2 net-next] net/mlx4_en: avoid one cache line miss to ring doorbell
@ 2021-10-01 0:52 Eric Dumazet
2021-10-03 8:05 ` Tariq Toukan
0 siblings, 1 reply; 2+ messages in thread
From: Eric Dumazet @ 2021-10-01 0:52 UTC (permalink / raw)
To: David S . Miller, Jakub Kicinski
Cc: netdev, Eric Dumazet, Eric Dumazet, Tariq Toukan
From: Eric Dumazet <edumazet@google.com>
This patch caches doorbell address directly in struct mlx4_en_tx_ring.
This removes the need to bring in cpu caches whole struct mlx4_uar
in fast path.
Note that mlx4_uar is not guaranteed to be on a local node,
because mlx4_bf_alloc() uses a single free list (priv->bf_list)
regardless of its node parameter.
This kind of change does matter in presence of light/moderate traffic.
In high stress, this read-only line would be kept hot in caches.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tariq Toukan <tariqt@nvidia.com>
---
V2: added __iomem attribute to remove sparse errors (Jakub)
drivers/net/ethernet/mellanox/mlx4/en_tx.c | 4 ++--
drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 1 +
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index c56b9dba4c71898b61e87fd32e5fa523c313e445..817f4154b86d599cd593876ec83529051d95fe2f 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -130,6 +130,7 @@ int mlx4_en_create_tx_ring(struct mlx4_en_priv *priv,
ring->bf_enabled = !!(priv->pflags &
MLX4_EN_PRIV_FLAGS_BLUEFLAME);
}
+ ring->doorbell_address = ring->bf.uar->map + MLX4_SEND_DOORBELL;
ring->hwtstamp_tx_type = priv->hwtstamp_config.tx_type;
ring->queue_index = queue_index;
@@ -753,8 +754,7 @@ void mlx4_en_xmit_doorbell(struct mlx4_en_tx_ring *ring)
#else
iowrite32be(
#endif
- (__force u32)ring->doorbell_qpn,
- ring->bf.uar->map + MLX4_SEND_DOORBELL);
+ (__force u32)ring->doorbell_qpn, ring->doorbell_address);
}
static void mlx4_en_tx_write_desc(struct mlx4_en_tx_ring *ring,
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
index ad0a8b488832c8cdca2790e47fc778fe15686f7f..e132ff4c82f2d33045f6c9aeecaaa409a41e0b0d 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
@@ -283,6 +283,7 @@ struct mlx4_en_tx_ring {
struct mlx4_bf bf;
/* Following part should be mostly read */
+ void __iomem *doorbell_address;
__be32 doorbell_qpn;
__be32 mr_key;
u32 size; /* number of TXBBs */
--
2.33.0.800.g4c38ced690-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH V2 net-next] net/mlx4_en: avoid one cache line miss to ring doorbell
2021-10-01 0:52 [PATCH V2 net-next] net/mlx4_en: avoid one cache line miss to ring doorbell Eric Dumazet
@ 2021-10-03 8:05 ` Tariq Toukan
0 siblings, 0 replies; 2+ messages in thread
From: Tariq Toukan @ 2021-10-03 8:05 UTC (permalink / raw)
To: Eric Dumazet, David S . Miller, Jakub Kicinski
Cc: netdev, Eric Dumazet, Tariq Toukan
On 10/1/2021 3:52 AM, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
>
> This patch caches doorbell address directly in struct mlx4_en_tx_ring.
>
> This removes the need to bring in cpu caches whole struct mlx4_uar
> in fast path.
>
> Note that mlx4_uar is not guaranteed to be on a local node,
> because mlx4_bf_alloc() uses a single free list (priv->bf_list)
> regardless of its node parameter.
>
> This kind of change does matter in presence of light/moderate traffic.
> In high stress, this read-only line would be kept hot in caches.
>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Tariq Toukan <tariqt@nvidia.com>
> ---
> V2: added __iomem attribute to remove sparse errors (Jakub)
>
> drivers/net/ethernet/mellanox/mlx4/en_tx.c | 4 ++--
> drivers/net/ethernet/mellanox/mlx4/mlx4_en.h | 1 +
> 2 files changed, 3 insertions(+), 2 deletions(-)
>
Thanks for your patch.
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
^ permalink raw reply [flat|nested] 2+ messages in thread
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