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 <sagig@xxxxxxxxxxxx>
Reviewed-by: Steve Wise <swise@xxxxxxxxxxxxxxxxxxxxx>
---
drivers/infiniband/hw/mlx4/main.c | 2 +-
include/linux/mlx4/device.h | 11 +++++++++++
2 files changed, 12 insertions(+), 1 deletions(-)
diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
index 7026580..e0232a2 100644
--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -499,7 +499,7 @@ static int mlx4_ib_init_device_flags(struct ib_device *ibdev)
ibdev->max_qp_wr = dev->dev->caps.max_wqes - MLX4_IB_SQ_MAX_SPARE;
ibdev->max_sge = min(dev->dev->caps.max_sq_sg,
dev->dev->caps.max_rq_sg);
- ibdev->max_sge_rd = ibdev->max_sge;
+ ibdev->max_sge_rd = MLX4_MAX_SGE_RD;
ibdev->max_cq = dev->dev->quotas.cq;
ibdev->max_cqe = dev->dev->caps.max_cqes;
ibdev->max_mr = dev->dev->quotas.mpt;
diff --git a/include/linux/mlx4/device.h b/include/linux/mlx4/device.h
index dac6872..3dcae41 100644
--- a/include/linux/mlx4/device.h
+++ b/include/linux/mlx4/device.h
@@ -427,6 +427,17 @@ enum {
};
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,
MLX4_DEV_PMC_SUBTYPE_PKEY_TABLE = 0x16,
--
1.7.1
--
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