Re: [PATCH rdma-next v1 2/2] RDMA/core: Optimize XRC target lookup

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Jun 23, 2020 at 02:15:31PM +0300, Leon Romanovsky wrote:
> From: Maor Gottlieb <maorg@mellanox.com>
> 
> Replace the mutex with read write semaphore and use xarray instead
> of linked list for XRC target QPs. This will give faster XRC target
> lookup. In addition, when QP is closed, don't insert it back to the
> xarray if the destroy command failed.
> 
> Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
> Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
>  drivers/infiniband/core/verbs.c | 57 ++++++++++++---------------------
>  include/rdma/ib_verbs.h         |  5 ++-
>  2 files changed, 23 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/infiniband/core/verbs.c b/drivers/infiniband/core/verbs.c
> index d66a0ad62077..1ccbe43e33cd 100644
> +++ b/drivers/infiniband/core/verbs.c
> @@ -1090,13 +1090,6 @@ static void __ib_shared_qp_event_handler(struct ib_event *event, void *context)
>  	spin_unlock_irqrestore(&qp->device->qp_open_list_lock, flags);
>  }
>  
> -static void __ib_insert_xrcd_qp(struct ib_xrcd *xrcd, struct ib_qp *qp)
> -{
> -	mutex_lock(&xrcd->tgt_qp_mutex);
> -	list_add(&qp->xrcd_list, &xrcd->tgt_qp_list);
> -	mutex_unlock(&xrcd->tgt_qp_mutex);
> -}
> -
>  static struct ib_qp *__ib_open_qp(struct ib_qp *real_qp,
>  				  void (*event_handler)(struct ib_event *, void *),
>  				  void *qp_context)
> @@ -1139,16 +1132,15 @@ struct ib_qp *ib_open_qp(struct ib_xrcd *xrcd,
>  	if (qp_open_attr->qp_type != IB_QPT_XRC_TGT)
>  		return ERR_PTR(-EINVAL);
>  
> -	qp = ERR_PTR(-EINVAL);
> -	mutex_lock(&xrcd->tgt_qp_mutex);
> -	list_for_each_entry(real_qp, &xrcd->tgt_qp_list, xrcd_list) {
> -		if (real_qp->qp_num == qp_open_attr->qp_num) {
> -			qp = __ib_open_qp(real_qp, qp_open_attr->event_handler,
> -					  qp_open_attr->qp_context);
> -			break;
> -		}
> +	down_read(&xrcd->tgt_qps_rwsem);
> +	real_qp = xa_load(&xrcd->tgt_qps, qp_open_attr->qp_num);
> +	if (!real_qp) {

Don't we already have a xarray indexed against qp_num in res_track?
Can we use it somehow?

Jason