From a5e14ba334e202c58e45ef47414ec94c585c1a8c Mon Sep 17 00:00:00 2001 From: Sagi Grimberg Date: Wed, 28 Oct 2015 13:28:15 +0200 Subject: mlx4: Expose correct max_sge_rd limit mlx4 devices (ConnectX-2, ConnectX-3) 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. Signed-off-by: Sagi Grimberg Reviewed-by: Steve Wise Signed-off-by: Doug Ledford --- include/linux/mlx4/device.h | 11 +++++++++++ 1 file changed, 11 insertions(+) (limited to 'include') diff --git a/include/linux/mlx4/device.h b/include/linux/mlx4/device.h index 7501626ab529..d3133be12d92 100644 --- a/include/linux/mlx4/device.h +++ b/include/linux/mlx4/device.h @@ -426,6 +426,17 @@ enum { MLX4_MAX_FAST_REG_PAGES = 511, }; +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) + */ + MLX4_MAX_SGE_RD = (512 - 16 - 16) / 16 +}; + enum { MLX4_DEV_PMC_SUBTYPE_GUID_INFO = 0x14, MLX4_DEV_PMC_SUBTYPE_PORT_INFO = 0x15, -- cgit v1.2.3