netdev - Re: [PATCH rdma-next 4/4] RDMA/mlx5: Use query_special

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Message-ID: <Y7WFTULBGZ1WczxV@unreal>
Date:   Wed, 4 Jan 2023 15:55:25 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Or Har-Toov <ohartoov@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, linux-rdma@...r.kernel.org,
        Michael Guralnik <michaelgur@...dia.com>,
        netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH rdma-next 4/4] RDMA/mlx5: Use query_special_contexts for
 mkeys

On Wed, Jan 04, 2023 at 09:13:10AM -0400, Jason Gunthorpe wrote:
> On Wed, Jan 04, 2023 at 03:09:54PM +0200, Leon Romanovsky wrote:
> > On Wed, Jan 04, 2023 at 09:03:06AM -0400, Jason Gunthorpe wrote:
> > > On Wed, Jan 04, 2023 at 10:11:25AM +0200, Leon Romanovsky wrote:
> > > > -int mlx5_cmd_null_mkey(struct mlx5_core_dev *dev, u32 *null_mkey)
> > > > -{
> > > > -	u32 out[MLX5_ST_SZ_DW(query_special_contexts_out)] = {};
> > > > -	u32 in[MLX5_ST_SZ_DW(query_special_contexts_in)] = {};
> > > > -	int err;
> > > > +	err = mlx5_cmd_exec_inout(dev->mdev, query_special_contexts, in, out);
> > > > +	if (err)
> > > > +		return err;
> > > >  
> > > > -	MLX5_SET(query_special_contexts_in, in, opcode,
> > > > -		 MLX5_CMD_OP_QUERY_SPECIAL_CONTEXTS);
> > > > -	err = mlx5_cmd_exec_inout(dev, query_special_contexts, in, out);
> > > > -	if (!err)
> > > > -		*null_mkey = MLX5_GET(query_special_contexts_out, out,
> > > > -				      null_mkey);
> > > > -	return err;
> > > > +	if (MLX5_CAP_GEN(dev->mdev, dump_fill_mkey))
> > > > +		dev->mkeys.dump_fill_mkey = MLX5_GET(query_special_contexts_out,
> > > > +						     out, dump_fill_mkey);
> > > > +
> > > > +	if (MLX5_CAP_GEN(dev->mdev, null_mkey))
> > > > +		dev->mkeys.null_mkey = cpu_to_be32(
> > > > +			MLX5_GET(query_special_contexts_out, out, null_mkey));
> > > > +
> > > > +	if (MLX5_CAP_GEN(dev->mdev, terminate_scatter_list_mkey)) {
> > > > +		dev->mkeys.terminate_scatter_list_mkey =
> > > > +			cpu_to_be32(MLX5_GET(query_special_contexts_out, out,
> > > > +					     terminate_scatter_list_mkey));
> > > > +		return 0;
> > > > +	}
> > > > +	dev->mkeys.terminate_scatter_list_mkey =
> > > > +		MLX5_TERMINATE_SCATTER_LIST_LKEY;
> > > 
> > > This is already stored in the core dev, why are you recalculating it
> > > here?
> > 
> > It is not recalculating but setting default value. In core dev, we will
> > have value only if MLX5_CAP_GEN(dev->mdev, terminate_scatter_list_mkey)
> > is true.
> 
> No, it has the identical code:
> 
> +static int mlx5_get_terminate_scatter_list_mkey(struct mlx5_core_dev *dev)
> +{
> +       if (MLX5_CAP_GEN(dev, terminate_scatter_list_mkey)) {
> +               dev->terminate_scatter_list_mkey =
> +                       cpu_to_be32(MLX5_GET(query_special_contexts_out, out,
> +                                            terminate_scatter_list_mkey));
> +               return 0;
> +       }
> +       dev->terminate_scatter_list_mkey = MLX5_TERMINATE_SCATTER_LIST_LKEY;

Ahh, you are talking about that.
terminate_scatter_list_mkey is part of an output from MLX5_CMD_OP_QUERY_SPECIAL_CONTEXTS,
which is needed to get other mkeys. So instead of doing special logic
for the terminate_scatter_list_mkey, we decided to use same pattern as
for other mkeys, which don't belong to core.

Thanks

> 
> Jason