Re: [PATCH 1/2] mlx4: Expose correct max_sge_rd limit

[Or Gerlitz <ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>]

On 10/27/2015 11:40 AM, Sagi Grimberg wrote:
> mlx4 devices (ConnectX-2, ConnectX-3) can not issue
> max_sge in a single RDMA_READ request (resulting in
> a completion error). Thus, expose lower max_sge_rd
> to avoid this issue.

Sagi,

I can hear your pain when wearing the iser target driver maintainer hat.

Still, this patch is currently pure WA b/c we didn't do RCA (Root Cause 
Analysis)

Lets wait for RCA (which might yield the same patch, BTW) and keep 
suffering in LIO

Or.


>
> Signed-off-by: Sagi Grimberg <sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> ---
>   drivers/infiniband/hw/mlx4/main.c |    3 ++-
>   1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
> index 3889723..46305dc 100644
> --- a/drivers/infiniband/hw/mlx4/main.c
> +++ b/drivers/infiniband/hw/mlx4/main.c
> @@ -499,7 +499,8 @@ 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;
> +	/* reserve 2 sge slots for rdma reads */
> +	ibdev->max_sge_rd	   = ibdev->max_sge - 2;
>   	ibdev->max_cq		   = dev->dev->quotas.cq;
>   	ibdev->max_cqe		   = dev->dev->caps.max_cqes;
>   	ibdev->max_mr		   = dev->dev->quotas.mpt;

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