netdev - Re: [PATCH 04/38] mlx5: Convert cq

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Date:   Tue, 27 Aug 2019 19:22:39 +0000
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     "willy@...radead.org" <willy@...radead.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH 04/38] mlx5: Convert cq_table to XArray

On Tue, 2019-08-20 at 15:32 -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> Since mlx5_cq_table would have shrunk down to just the xarray,
> eliminate
> it and embed the xarray directly into mlx5_eq.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/eq.c  | 27 ++++-------------
> --
>  .../net/ethernet/mellanox/mlx5/core/lib/eq.h  |  7 +----
>  2 files changed, 6 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> index 09d4c64b6e73..c5953f6e0a69 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> @@ -113,11 +113,10 @@ static int mlx5_cmd_destroy_eq(struct
> mlx5_core_dev *dev, u8 eqn)
>  /* caller must eventually call mlx5_cq_put on the returned cq */
>  static struct mlx5_core_cq *mlx5_eq_cq_get(struct mlx5_eq *eq, u32
> cqn)
>  {
> -	struct mlx5_cq_table *table = &eq->cq_table;
> -	struct mlx5_core_cq *cq = NULL;
> +	struct mlx5_core_cq *cq;
>  
>  	rcu_read_lock();
> -	cq = radix_tree_lookup(&table->tree, cqn);
> +	cq = xa_load(&eq->cq_table, cqn);
>  	if (likely(cq))
>  		mlx5_cq_hold(cq);
>  	rcu_read_unlock();
> @@ -243,7 +242,6 @@ static int
>  create_map_eq(struct mlx5_core_dev *dev, struct mlx5_eq *eq,
>  	      struct mlx5_eq_param *param)
>  {
> -	struct mlx5_cq_table *cq_table = &eq->cq_table;
>  	u32 out[MLX5_ST_SZ_DW(create_eq_out)] = {0};
>  	struct mlx5_priv *priv = &dev->priv;
>  	u8 vecidx = param->irq_index;
> @@ -254,11 +252,7 @@ create_map_eq(struct mlx5_core_dev *dev, struct
> mlx5_eq *eq,
>  	int err;
>  	int i;
>  
> -	/* Init CQ table */
> -	memset(cq_table, 0, sizeof(*cq_table));
> -	spin_lock_init(&cq_table->lock);
> -	INIT_RADIX_TREE(&cq_table->tree, GFP_ATOMIC);
> -
> +	xa_init_flags(&eq->cq_table, XA_FLAGS_LOCK_IRQ);

Why the IRQ flag ? we are not going to modify the xarray in irq context
all we do is hold a ref count on the entry we looked up
mlx5_cq_hold(cq); and this is protected by rcu_lock. 

>  	eq->nent = roundup_pow_of_two(param->nent +
> MLX5_NUM_SPARE_EQE);
>  	eq->cons_index = 0;
>  	err = mlx5_buf_alloc(dev, eq->nent * MLX5_EQE_SIZE, &eq->buf);
> @@ -378,25 +372,14 @@ static int destroy_unmap_eq(struct
> mlx5_core_dev *dev, struct mlx5_eq *eq)
>  
>  int mlx5_eq_add_cq(struct mlx5_eq *eq, struct mlx5_core_cq *cq)
>  {
> -	struct mlx5_cq_table *table = &eq->cq_table;
> -	int err;
> -
> -	spin_lock(&table->lock);
> -	err = radix_tree_insert(&table->tree, cq->cqn, cq);
> -	spin_unlock(&table->lock);
> -
> -	return err;
> +	return xa_err(xa_store(&eq->cq_table, cq->cqn, cq,
> GFP_KERNEL));
>  }
>  
>  void mlx5_eq_del_cq(struct mlx5_eq *eq, struct mlx5_core_cq *cq)
>  {
> -	struct mlx5_cq_table *table = &eq->cq_table;
>  	struct mlx5_core_cq *tmp;
>  
> -	spin_lock(&table->lock);
> -	tmp = radix_tree_delete(&table->tree, cq->cqn);
> -	spin_unlock(&table->lock);
> -
> +	tmp = xa_erase(&eq->cq_table, cq->cqn);
>  	if (!tmp) {
>  		mlx5_core_dbg(eq->dev, "cq 0x%x not found in eq 0x%x
> tree\n",
>  			      eq->eqn, cq->cqn);
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/eq.h
> b/drivers/net/ethernet/mellanox/mlx5/core/lib/eq.h
> index 4be4d2d36218..a342cf78120e 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/lib/eq.h
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/eq.h
> @@ -16,14 +16,9 @@ struct mlx5_eq_tasklet {
>  	spinlock_t            lock; /* lock completion tasklet list */
>  };
>  
> -struct mlx5_cq_table {
> -	spinlock_t              lock;	/* protect radix tree */
> -	struct radix_tree_root  tree;
> -};
> -
>  struct mlx5_eq {
>  	struct mlx5_core_dev    *dev;
> -	struct mlx5_cq_table    cq_table;
> +	struct xarray		cq_table;
>  	__be32 __iomem	        *doorbell;
>  	u32                     cons_index;
>  	struct mlx5_frag_buf    buf;