Subject: Re: [PATCH for-next v3 1/2] IB/cma: Introduce rdma_set_min_rnr_timer()

From: Leon Romanovsky <[email-masked]>
Date: Thu, 1 Apr 2021 13:54:16 +0300

On Wed, Mar 31, 2021 at 08:43:13PM +0200, Håkon Bugge wrote:
> Introduce the ability for kernel ULPs to adjust the minimum RNR Retry
> timer. The INIT -> RTR transition executed by RDMA CM will be used for
> this adjustment. This avoids an additional ib_modify_qp() call.
> 
> rdma_set_min_rnr_timer() must be called before the call to
> rdma_connect() on the active side and before the call to rdma_accept()
> on the passive side.
> 
> The default value of RNR Retry timer is zero, which translates to 655
> ms. When the receiver is not ready to accept a send messages, it
> encodes the RNR Retry timer value in the NAK. The requestor will then
> wait at least the specified time value before retrying the send.
> 
> The 5-bit value to be supplied to the rdma_set_min_rnr_timer() is
> documented in IBTA Table 45: "Encoding for RNR NAK Timer Field".
> 
> Signed-off-by: Håkon Bugge <[email-masked]>
> Acked-by: Jason Gunthorpe <[email-masked]>
> ---
>  drivers/infiniband/core/cma.c      | 41 ++++++++++++++++++++++++++++++++++++++
>  drivers/infiniband/core/cma_priv.h |  2 ++
>  include/rdma/rdma_cm.h             |  2 ++
>  3 files changed, 45 insertions(+)
> 
> diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
> index 9409651..5ce097d 100644
> --- a/drivers/infiniband/core/cma.c
> +++ b/drivers/infiniband/core/cma.c
> @@ -852,6 +852,7 @@ static void cma_id_put(struct rdma_id_private *id_priv)
>  	id_priv->id.qp_type = qp_type;
>  	id_priv->tos_set = false;
>  	id_priv->timeout_set = false;
> +	id_priv->min_rnr_timer_set = false;
>  	id_priv->gid_type = IB_GID_TYPE_IB;
>  	spin_lock_init(&id_priv->lock);
>  	mutex_init(&id_priv->qp_mutex);
> @@ -1141,6 +1142,9 @@ int rdma_init_qp_attr(struct rdma_cm_id *id, struct ib_qp_attr *qp_attr,
>  	if ((*qp_attr_mask & IB_QP_TIMEOUT) && id_priv->timeout_set)
>  		qp_attr->timeout = id_priv->timeout;
>  
> +	if ((*qp_attr_mask & IB_QP_MIN_RNR_TIMER) && id_priv->min_rnr_timer_set)
> +		qp_attr->min_rnr_timer = id_priv->min_rnr_timer;
> +
>  	return ret;
>  }
>  EXPORT_SYMBOL(rdma_init_qp_attr);
> @@ -2615,6 +2619,43 @@ int rdma_set_ack_timeout(struct rdma_cm_id *id, u8 timeout)
>  }
>  EXPORT_SYMBOL(rdma_set_ack_timeout);
>  
> +/**
> + * rdma_set_min_rnr_timer() - Set the minimum RNR Retry timer of the
> + *			      QP associated with a connection identifier.
> + * @id: Communication identifier to associated with service type.
> + * @min_rnr_timer: 5-bit value encoded as Table 45: "Encoding for RNR NAK
> + *		   Timer Field" in the IBTA specification.
> + *
> + * This function should be called before rdma_connect() on active
> + * side, and on passive side before rdma_accept(). The timer value
> + * will be associated with the local QP. When it receives a send it is
> + * not read to handle, typically if the receive queue is empty, an RNR
> + * Retry NAK is returned to the requester with the min_rnr_timer
> + * encoded. The requester will then wait at least the time specified
> + * in the NAK before retrying. The default is zero, which translates
> + * to a minimum RNR Timer value of 655 ms.
> + *
> + * Return: 0 for success
> + */
> +int rdma_set_min_rnr_timer(struct rdma_cm_id *id, u8 min_rnr_timer)
> +{
> +	struct rdma_id_private *id_priv;
> +
> +	/* It is a five-bit value */
> +	if (min_rnr_timer & 0xe0)
> +		return -EINVAL;
> +
> +	if (id->qp_type != IB_QPT_RC && id->qp_type != IB_QPT_XRC_TGT)
> +		return -EINVAL;

This is in-kernel API and safe to use WARN_ON() instead of returning
error which RDS is not checking anyway.

Thanks