[PATCH net-next, v3] net/mlx5: Use dma_wmb() for completion queue doorbell updates
From: lirongqing <hidden>
Date: 2026-08-16 03:56:27
Also in:
bpf, linux-rdma, lkml
Subsystem:
mellanox ethernet driver (mlx5e), mellanox ethernet innova drivers, mellanox mlx5 core vpi driver, networking drivers, the rest, xdp (express data path) · Maintainers:
Saeed Mahameed, Tariq Toukan, Mark Bloch, Leon Romanovsky, Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, Alexei Starovoitov, Daniel Borkmann, Jesper Dangaard Brouer, John Fastabend
From: Li RongQing <redacted> dma_*() barriers are specifically for ordering writes to DMA coherent memory that is accessible to both the CPU and DMA capable devices. The dma_wmb() barrier is lighter than wmb() on some architectures because it only ensures ordering for DMA writes, not for all writes including MMIO accesses. In the MLX5 driver, completion queue (CQ) doorbell records are allocated as DMA coherent memory via mlx5_dma_zalloc_coherent_node(). The CQ update pattern is: 1. Update CQ space (device reads via DMA) 2. Update doorbell record (device reads via DMA) 3. Memory barrier 4. Enable more CQEs Since only DMA coherent memory accesses are involved (no MMIO accesses follow), we can safely use dma_wmb() instead of wmb(). This change improves performance slightly on architectures where dma_wmb() is lighter than wmb(). Signed-off-by: Li RongQing <redacted> Signed-off-by: Tariq Toukan <tariqt@nvidia.com> --- V3: Kept the original wmb() barrier inside wc.c V2: rebased. https://patchwork.kernel.org/project/netdevbpf/patch/20260811064750.3218024-1-tariqt@nvidia.com/ V1: https://patchwork.kernel.org/project/netdevbpf/patch/20260402055206.2311-1-lirongqing@baidu.com/ drivers/net/ethernet/mellanox/mlx5/core/en/ptp.c | 2 +- drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c | 2 +- drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 2 +- drivers/net/ethernet/mellanox/mlx5/core/en_tx.c | 2 +- drivers/net/ethernet/mellanox/mlx5/core/fpga/conn.c | 2 +- drivers/net/ethernet/mellanox/mlx5/core/lib/aso.c | 2 +- 6 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/ptp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/ptp.c
index 723f66a..17084d7 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/ptp.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/ptp.c@@ -259,7 +259,7 @@ static bool mlx5e_ptp_poll_ts_cq(struct mlx5e_cq *cq, int napi_budget) mlx5_cqwq_update_db_record(cqwq); /* ensure cq space is freed before enabling more cqes */ - wmb(); + dma_wmb(); while (metadata_buff_sz > 0) mlx5e_ptp_metadata_fifo_push(&ptpsq->metadata_freelist,
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
index 77ea51b..ee0986b 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/xdp.c@@ -817,7 +817,7 @@ bool mlx5e_poll_xdpsq_cq(struct mlx5e_cq *cq) mlx5_cqwq_update_db_record(&cq->wq); /* ensure cq space is freed before enabling more cqes */ - wmb(); + dma_wmb(); sq->cc = sqcc; return (i == MLX5E_TX_CQ_POLL_BUDGET);
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 6fbc044..3c80193 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c@@ -2507,7 +2507,7 @@ int mlx5e_poll_rx_cq(struct mlx5e_cq *cq, int budget) mlx5_cqwq_update_db_record(cqwq); /* ensure cq space is freed before enabling more cqes */ - wmb(); + dma_wmb(); return work_done; }
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
index 0b5e600..14479da 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c@@ -849,7 +849,7 @@ bool mlx5e_poll_tx_cq(struct mlx5e_cq *cq, int napi_budget) mlx5_cqwq_update_db_record(&cq->wq); /* ensure cq space is freed before enabling more cqes */ - wmb(); + dma_wmb(); sq->dma_fifo_cc = dma_fifo_cc; sq->cc = sqcc;
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fpga/conn.c b/drivers/net/ethernet/mellanox/mlx5/core/fpga/conn.c
index 1f6bde5..1341874 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/fpga/conn.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/fpga/conn.c@@ -384,7 +384,7 @@ static inline void mlx5_fpga_conn_cqes(struct mlx5_fpga_conn *conn, mlx5_fpga_dbg(conn->fdev, "Re-arming CQ with cc# %u\n", conn->cq.wq.cc); /* ensure cq space is freed before enabling more cqes */ - wmb(); + dma_wmb(); mlx5_fpga_conn_arm_cq(conn); }
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/aso.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/aso.c
index 614cd57..8f7a89a 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/lib/aso.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/aso.c@@ -421,7 +421,7 @@ int mlx5_aso_poll_cq(struct mlx5_aso *aso, bool with_data) mlx5_cqwq_update_db_record(&cq->wq); /* ensure cq space is freed before enabling more cqes */ - wmb(); + dma_wmb(); if (with_data) aso->cc += MLX5_ASO_WQEBBS_DATA;
--
2.9.4