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 Mon, Apr 30, 2018 at 1:38 PM, Jason Gunthorpe <jgg@xxxxxxxxxxxx> wrote:
>
> 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..

Makes sense. Are you referring to the Parent Domain or the Protection
Domain by PD here?

-Rohit
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