On Wed, Jun 12, 2019 at 03:12:27PM +0300, Leon Romanovsky wrote:
> On Wed, Jun 12, 2019 at 09:08:02AM -0300, Jason Gunthorpe wrote:
> > On Wed, Jun 12, 2019 at 12:01:23PM +0000, Mark Zhang wrote:
> > > On 6/12/2019 1:54 AM, Jason Gunthorpe wrote:
> > > > On Thu, Jun 06, 2019 at 01:53:37PM +0300, Leon Romanovsky wrote:
> > > >> From: Mark Zhang <markz@xxxxxxxxxxxx>
> > > >>
> > > >> Add support for ib callbacks counter_bind_qp() and counter_unbind_qp().
> > > >>
> > > >> Signed-off-by: Mark Zhang <markz@xxxxxxxxxxxx>
> > > >> Reviewed-by: Majd Dibbiny <majd@xxxxxxxxxxxx>
> > > >> Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxxxx>
> > > >> drivers/infiniband/hw/mlx5/main.c | 53 +++++++++++++++++++++++++++++++
> > > >> 1 file changed, 53 insertions(+)
> > > >>
> > > >> diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
> > > >> index 8b7bcf8f68fb..66c94a060718 100644
> > > >> +++ b/drivers/infiniband/hw/mlx5/main.c
> > > >> @@ -5533,6 +5533,57 @@ static int mlx5_ib_get_hw_stats(struct ib_device *ibdev,
> > > >> return num_counters;
> > > >> }
> > > >>
> > > >> +static int mlx5_ib_counter_bind_qp(struct rdma_counter *counter,
> > > >> + struct ib_qp *qp)
> > > >> +{
> > > >> + struct mlx5_ib_dev *dev = to_mdev(qp->device);
> > > >> + u16 cnt_set_id = 0;
> > > >> + int err;
> > > >> +
> > > >> + if (!counter->id) {
> > > >> + err = mlx5_cmd_alloc_q_counter(dev->mdev,
> > > >> + &cnt_set_id,
> > > >> + MLX5_SHARED_RESOURCE_UID);
> > > >> + if (err)
> > > >> + return err;
> > > >> + counter->id = cnt_set_id;
> > > >> + }
> > > >> +
> > > >> + err = mlx5_ib_qp_set_counter(qp, counter);
> > > >> + if (err)
> > > >> + goto fail_set_counter;
> > > >> +
> > > >> + return 0;
> > > >> +
> > > >> +fail_set_counter:
> > > >> + mlx5_core_dealloc_q_counter(dev->mdev, cnt_set_id);
> > > >> + counter->id = 0;
> > > >> +
> > > >> + return err;
> > > >> +}
> > > >> +
> > > >> +static int mlx5_ib_counter_unbind_qp(struct ib_qp *qp, bool force)
> > > >> +{
> > > >> + struct mlx5_ib_dev *dev = to_mdev(qp->device);
> > > >> + struct rdma_counter *counter = qp->counter;
> > > >> + int err;
> > > >> +
> > > >> + err = mlx5_ib_qp_set_counter(qp, NULL);
> > > >> + if (err && !force)
> > > >> + return err;
> > > >> +
> > > >> + /*
> > > >> + * Deallocate the counter if this is the last QP bound on it;
> > > >> + * If @force is set then we still deallocate the q counter
> > > >> + * no matter if there's any error in previous. used for cases
> > > >> + * like qp destroy.
> > > >> + */
> > > >> + if (atomic_read(&counter->usecnt) == 1)
> > > >> + return mlx5_core_dealloc_q_counter(dev->mdev, counter->id);
> > > >
> > > > This looks like a nonsense thing to write, what it is trying to do
> > > > with that atomic?
> > > >
> > > > I still can't see why this isn't a normal kref.
> > > >
> > >
> > > Hi Jason,
> > >
> > > Have discussed with Leon, unlike other resources, counter alloc/dealloc
> > > isn't called explicitly. So we need a refcount to record how many QPs
> > > are bound on this counter, when it comes to 0 then the counter can be
> > > deallocated. Whether to use atomic or kref the code is similar, it is
> > > not able to take advantage of kref/completion.
> >
> > That doesn't explain the nonsense "atomic_read(&counter->usecnt) == 1"
> > test
>
> It means that all QPs "returned" this counter.
It doesn't make sense to do something like that with an atomic, either
you know there is no possible atomic_inc/dec at this point (which begs the
question why test it), or it is racy
Jason
