From: Sagi Grimberg <sagig@xxxxxxxxxxx>
mlx5 devices (Connect-IB, ConnectX-4, ConnectX-4-LX) has a limitation
where rdma read work queue entries cannot exceed 512 bytes.
A rdma_read wqe needs to fit in 512 bytes:
- wqe control segment (16 bytes)
- rdma segment (16 bytes)
- scatter elements (16 bytes each)
So max_sge_rd should be: (512 - 16 - 16) / 16 = 30.
Reported-by: Christoph Hellwig <hch@xxxxxx>
Tested-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Sagi Grimberg <sagig@xxxxxxxxxxx>
---
drivers/infiniband/hw/mlx5/main.c | 2 +-
include/linux/mlx5/device.h | 11 +++++++++++
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index 5acf346..049754f 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -530,7 +530,7 @@ static int mlx5_ib_query_device(struct ib_device *ibdev,
sizeof(struct mlx5_wqe_ctrl_seg)) /
sizeof(struct mlx5_wqe_data_seg);
props->max_sge = min(max_rq_sg, max_sq_sg);
- props->max_sge_rd = props->max_sge;
+ props->max_sge_rd = MLX5_MAX_SGE_RD;
props->max_cq = 1 << MLX5_CAP_GEN(mdev, log_max_cq);
props->max_cqe = (1 << MLX5_CAP_GEN(mdev, log_max_cq_sz)) - 1;
props->max_mr = 1 << MLX5_CAP_GEN(mdev, log_max_mkey);
diff --git a/include/linux/mlx5/device.h b/include/linux/mlx5/device.h
index 8156e3c..b3575f3 100644
--- a/include/linux/mlx5/device.h
+++ b/include/linux/mlx5/device.h
@@ -392,6 +392,17 @@ enum {
MLX5_CAP_OFF_CMDIF_CSUM = 46,
};
+enum {
+ /*
+ * Max wqe size for rdma read is 512 bytes, so this
+ * limits our max_sge_rd as the wqe needs to fit:
+ * - ctrl segment (16 bytes)
+ * - rdma segment (16 bytes)
+ * - scatter elements (16 bytes each)
+ */
+ MLX5_MAX_SGE_RD = (512 - 16 - 16) / 16
+};
+
struct mlx5_inbox_hdr {
__be16 opcode;
u8 rsvd[4];
--
2.1.4
--
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