Re: [PATCH v9 1/3] mempool: support external mempool operations

[Olivier Matz <olivier.matz@6wind.com>]

Hi David,

Some comments below.

On 06/10/2016 05:16 PM, David Hunt wrote:
> Until now, the objects stored in a mempool were internally stored in a
> ring. This patch introduces the possibility to register external handlers
> replacing the ring.
> 
> The default behavior remains unchanged, but calling the new function
> rte_mempool_set_handler() right after rte_mempool_create_empty() allows
> the user to change the handler that will be used when populating
> the mempool.
> 
> This patch also adds a set of default ops (function callbacks) based
> on rte_ring.
> 
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> Signed-off-by: David Hunt <david.hunt@intel.com>
> 

> ...
> @@ -386,10 +352,14 @@ rte_mempool_populate_phys(struct rte_mempool *mp, char *vaddr,
>  	int ret;
>  
>  	/* create the internal ring if not already done */
> -	if ((mp->flags & MEMPOOL_F_RING_CREATED) == 0) {
> -		ret = rte_mempool_ring_create(mp);
> -		if (ret < 0)
> -			return ret;
> +	if ((mp->flags & MEMPOOL_F_POOL_CREATED) == 0) {
> +		rte_errno = 0;
> +		ret = rte_mempool_ops_alloc(mp);
> +		if (ret != 0) {
> +			if (rte_errno == 0)
> +				return -EINVAL;
> +			return -rte_errno;
> +		}
>  	}

The rte_errno should be removed. Just return the error code from
rte_mempool_ops_alloc() on failure.

> +/** Structure defining mempool operations structure */
> +struct rte_mempool_ops {
> +	char name[RTE_MEMPOOL_OPS_NAMESIZE]; /**< Name of mempool ops struct */
> +	rte_mempool_alloc_t alloc;       /**< Allocate private data */
> +	rte_mempool_free_t free;         /**< Free the external pool. */
> +	rte_mempool_put_t put;           /**< Put an object. */
> +	rte_mempool_get_t get;           /**< Get an object. */
> +	rte_mempool_get_count get_count; /**< Get qty of available objs. */
> +} __rte_cache_aligned;
> +

Sorry, I missed that in the previous reviews, but since the get/put
functions have been renamed in dequeue/enqueue, I think the same change
should also be done here.


> +/**
> + * Prototype for implementation specific data provisioning function.
> + *
> + * The function should provide the implementation specific memory for
> + * for use by the other mempool ops functions in a given mempool ops struct.
> + * E.g. the default ops provides an instance of the rte_ring for this purpose.
> + * it will most likely point to a different type of data structure, and
> + * will be transparent to the application programmer.
> + */
> +typedef int (*rte_mempool_alloc_t)(struct rte_mempool *mp);

A comment saying that this function should set mp->pool_data
would be nice here, I think.


> +/* wrapper to allocate an external mempool's private (pool) data */
> +int
> +rte_mempool_ops_alloc(struct rte_mempool *mp)
> +{
> +	struct rte_mempool_ops *ops;
> +
> +	ops = rte_mempool_ops_get(mp->ops_index);
> +	if (ops->alloc == NULL)
> +		return -ENOMEM;
> +	return ops->alloc(mp);
> +}

Now that we check that ops->alloc != NULL in the register function,
I wonder if we should keep this test or not. Yes, it doesn't hurt,
but for consistency with the other functions (get/put/get_count),
we may remove it.

This would be a good thing because it would prevent any confusion
with rte_mempool_ops_get(), which returns a pointer to the ops struct
(and has nothing to do with ops->get()).



Regards,
Olivier