netdev - Re: [PATCH rdma-next v1 2/3] RDMA/mlx5: Separate DCI QP creation logic

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Date:   Wed, 23 Jun 2021 09:03:38 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Doug Ledford <dledford@...hat.com>,
        Lior Nahmanson <liorna@...dia.com>,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Meir Lichtinger <meirl@...dia.com>, netdev@...r.kernel.org,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH rdma-next v1 2/3] RDMA/mlx5: Separate DCI QP creation
 logic

On Tue, Jun 22, 2021 at 03:45:56PM -0300, Jason Gunthorpe wrote:
> On Mon, Jun 21, 2021 at 10:06:15AM +0300, Leon Romanovsky wrote:
> > From: Lior Nahmanson <liorna@...dia.com>
> > 
> > This patch isolates DCI QP creation logic to separate function, so this
> > change will reduce complexity when adding new features to DCI QP without
> > interfering with other QP types.
> > 
> > The code was copied from create_user_qp() while taking only DCI relevant bits.
> > 
> > Reviewed-by: Meir Lichtinger <meirl@...dia.com>
> > Signed-off-by: Lior Nahmanson <liorna@...dia.com>
> > Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> >  drivers/infiniband/hw/mlx5/qp.c | 157 ++++++++++++++++++++++++++++++++
> >  1 file changed, 157 insertions(+)
> > 
> > diff --git a/drivers/infiniband/hw/mlx5/qp.c b/drivers/infiniband/hw/mlx5/qp.c
> > index 7a5f1eba60e3..65a380543f5a 100644
> > +++ b/drivers/infiniband/hw/mlx5/qp.c
> > @@ -1974,6 +1974,160 @@ static int create_xrc_tgt_qp(struct mlx5_ib_dev *dev, struct mlx5_ib_qp *qp,
> >  	return 0;
> >  }
> >  
> > +static int create_dci(struct mlx5_ib_dev *dev, struct ib_pd *pd,
> > +		      struct mlx5_ib_qp *qp,
> > +		      struct mlx5_create_qp_params *params)
> > +{
> 
> This is a huge amount of copying just to add 4 lines, why?
> 
> There must be a better way to do this qp stuff.
> 
> Why not put more stuff in _create_user_qp()?

Lior proposed it in original patch, but I didn't like it. It caused to
mix of various QP types and maze of "if () else ()" that are not applicable
one to another.

The huge _create_user_qp() is the reason why create_dci() is not small,
we simply had hard time to understand if specific HW bit is needed or
not in DCI flow.

My goal is to have small per-QP type specific functions that calls
to simple functions for very narrow scope.

Something like that:
static int create_dci(...)
{
  ...
  configure_send_cq(..)
  configure_recv_sq(..)
  configure_srq(...)
  ...
}

static int create_user_qp(...)
{
  ...
  configure_send_cq(..)
  configure_recv_sq(..)
  configure_srq(...)
  ...
}


Thanks

> 
> Jason