On 10/28/2015 07:28 AM, Sagi Grimberg wrote:
> 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;
What code tree did you make this patch from? Because in an upstream 4.4
kernel, there is no function mlx4_ib_init_device_flags(), but there is
mlx4_ib_query_device() that does much the same thing. But in there,
there is no ibdev->max_sge_rd, there is props->max_sge_rd. It's like
this came from an entirely different source base somewhere.
> 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,
>
--
Doug Ledford <dledford@xxxxxxxxxx>
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