Re: [dpdk-dev] [PATCH] mempool: Reduce rte_mempool structure size

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

Hi Keith,

Looks good, thanks. Please find some comments below.

> [PATCH] mempool: Reduce rte_mempool structure size

nit: we usually avoid uppercase letters in title

On 02/03/2016 12:02 AM, Keith Wiles wrote:
> diff --git a/lib/librte_mempool/rte_mempool.c b/lib/librte_mempool/rte_mempool.c
> index aff5f6d..bdf8e2e 100644
> --- a/lib/librte_mempool/rte_mempool.c
> +++ b/lib/librte_mempool/rte_mempool.c
> @@ -450,15 +450,11 @@ rte_mempool_xmem_create(const char *name, unsigned n, unsigned elt_size,
>  	int page_size = getpagesize();
>  
>  	/* compilation-time checks */
> +#ifdef RTE_LIBRTE_MEMPOOL_DEBUG
>  	RTE_BUILD_BUG_ON((sizeof(struct rte_mempool) &
>  			  RTE_CACHE_LINE_MASK) != 0);
> -#if RTE_MEMPOOL_CACHE_MAX_SIZE > 0
>  	RTE_BUILD_BUG_ON((sizeof(struct rte_mempool_cache) &
>  			  RTE_CACHE_LINE_MASK) != 0);
> -	RTE_BUILD_BUG_ON((offsetof(struct rte_mempool, local_cache) &
> -			  RTE_CACHE_LINE_MASK) != 0);
> -#endif
> -#ifdef RTE_LIBRTE_MEMPOOL_DEBUG

I don't think the #ifdef RTE_LIBRTE_MEMPOOL_DEBUG should be moved.
It should only protects the checks on stats which are enabled
in debug mode.

> @@ -194,10 +192,7 @@ struct rte_mempool {
>  
>  	unsigned private_data_size;      /**< Size of private data. */
>  
> -#if RTE_MEMPOOL_CACHE_MAX_SIZE > 0
> -	/** Per-lcore local cache. */
> -	struct rte_mempool_cache local_cache[RTE_MAX_LCORE];
> -#endif
> +	struct rte_mempool_cache *local_cache; /**< Per-lcore local cache */
>  
>  #ifdef RTE_LIBRTE_MEMPOOL_DEBUG
>  	/** Per-lcore statistics. */

As you noticed it in your initial mail, this changes the ABI. I
think your patch justifies the ABI change, so I think it should
follow the ABI change process described in
dpdk/doc/guides/contributing/versioning.rst.

>From what I understand of versioning.rst, these kind of changes
requires a deprecation notice first, and will be integrated in
next version. I don't think it's easy to keep a backward compat
in this case, especially because the rte_mempool structure is
used by several inlined functions.

Regards,
Olivier