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

[Maor Gottlieb <maorg@mellanox.com>]

On 6/24/2020 5:00 PM, Jason Gunthorpe wrote:
> On Wed, Jun 24, 2020 at 01:42:49PM +0300, Maor Gottlieb wrote:
>> On 6/23/2020 9:49 PM, Jason Gunthorpe wrote:
>>> On Tue, Jun 23, 2020 at 09:15:06PM +0300, Leon Romanovsky wrote:
>>>> On Tue, Jun 23, 2020 at 02:52:00PM -0300, Jason Gunthorpe wrote:
>>>>> 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?
>>>> We don't have restrack for XRC, we will need somehow manage QP-to-XRC
>>>> connection there.
>>> It is not xrc, this is just looking up a qp and checking if it is part
>>> of the xrcd
>>>
>>> Jason
>> It's the XRC target  QP and it is not tracked.
> Really? Something called 'real_qp' isn't stored in the restrack?
> Doesn't that sound like a bug already?
>
> Jason

Bug / limitation. see the below comment from core_priv.h:

         /*
          * We don't track XRC QPs for now, because they don't have PD
          * and more importantly they are created internaly by driver,
          * see mlx5 create_dev_resources() as an example.
          */

Leon, the PD is a real limitation? regarding the second part (mlx5),  
you just sent patches that change it,right?