Re: [PATCH rdma-core 2/2] mlx5: Disable locking on a QP if it is assigned to a thread domain

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On Fri, Apr 27, 2018 at 04:36:15AM +0000, Rohit Zambre wrote:
> By creating a QP within a thread domain the application is guaranteeing
> that the QP will not be accessed concurrently from multiple user threads.
> Hence, a lock is not needed for QP that is assigned to a thread domain.
> 
> This patch disables locking on the QP if a thread domain is passed during
> QP-creation.
> 
> Signed-off-by: Rohit Zambre <rzambre@xxxxxxx>
>  providers/mlx5/verbs.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/providers/mlx5/verbs.c b/providers/mlx5/verbs.c
> index 9fd765e..f7132e4 100644
> +++ b/providers/mlx5/verbs.c
> @@ -1607,6 +1607,7 @@ static struct ibv_qp *create_qp(struct ibv_context *context,
>  	struct mlx5_create_qp_ex_resp  resp_ex;
>  	struct mlx5_qp		       *qp;
>  	int				ret;
> +	int				thread_safe;
>  	struct mlx5_context	       *ctx = to_mctx(context);
>  	struct ibv_qp		       *ibqp;
>  	int32_t				usr_idx = 0;
> @@ -1751,8 +1752,14 @@ static struct ibv_qp *create_qp(struct ibv_context *context,
>  
>  	mlx5_init_qp_indices(qp);
>  
> -	if (mlx5_spinlock_init(&qp->sq.lock, !mlx5_single_threaded) ||
> -	    mlx5_spinlock_init(&qp->rq.lock, !mlx5_single_threaded))
> +	mparent_domain = to_mparent_domain(attr->pd);
> +	if (mparent_domain && mparent_domain->mtd)
> +		thread_safe = 1;
> +	else
> +		thread_safe = mlx5_single_threaded;
> +
> +	if (mlx5_spinlock_init(&qp->sq.lock, !thread_safe) ||
> +	    mlx5_spinlock_init(&qp->rq.lock, !thread_safe))
>  		goto err_free_qp_buf;

This would be nicer to have a 'mlx5_spinlock_init_pd' that takes the
object's pd and does the above calcuations.

All the remaining uses should be revised at once to use a pd if it
makes sense during the init..

Jason
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