Re: [dpdk-dev] [PATCH] mbuf: enforce alignment of mbuf private area

["Zhang, Helin" <helin.zhang@intel.com>]

> -----Original Message-----
> From: Olivier Matz [mailto:olivier.matz@6wind.com]
> Sent: Thursday, July 30, 2015 6:56 AM
> To: dev@dpdk.org
> Cc: Ananyev, Konstantin; olivier.matz@6wind.com; Zhang, Helin;
> martin.weiser@allegro-packets.com; thomas.monjalon@6wind.com
> Subject: [PATCH] mbuf: enforce alignment of mbuf private area
> 
> It looks better to have a data buffer address that is aligned to
> 8 bytes. This is the case when there is no mbuf private area, but if there is one,
> the alignment depends on the size of this area that is located between the mbuf
> structure and the data buffer.
> 
> Indeed, some drivers expects to have the buffer address aligned to an even
> address, and moreover an unaligned buffer may impact the performance when
> accessing to network headers.
> 
> Add a check in rte_pktmbuf_pool_create() to verify the alignment constraint
> before creating the mempool. For applications that use the alternative way
> (direct call to rte_mempool_create), also add an assertion in rte_pktmbuf_init().
> 
> By the way, also add the MBUF log type.
> 
> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> ---
>  lib/librte_eal/common/include/rte_log.h | 1 +
>  lib/librte_mbuf/rte_mbuf.c              | 8 +++++++-
>  lib/librte_mbuf/rte_mbuf.h              | 7 +++++--
>  3 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_eal/common/include/rte_log.h
> b/lib/librte_eal/common/include/rte_log.h
> index 24a55cc..ede0dca 100644
> --- a/lib/librte_eal/common/include/rte_log.h
> +++ b/lib/librte_eal/common/include/rte_log.h
> @@ -77,6 +77,7 @@ extern struct rte_logs rte_logs;
>  #define RTE_LOGTYPE_PORT    0x00002000 /**< Log related to port. */
>  #define RTE_LOGTYPE_TABLE   0x00004000 /**< Log related to table. */
>  #define RTE_LOGTYPE_PIPELINE 0x00008000 /**< Log related to pipeline. */
> +#define RTE_LOGTYPE_MBUF    0x00010000 /**< Log related to mbuf. */
> 
>  /* these log types can be used in an application */
>  #define RTE_LOGTYPE_USER1   0x01000000 /**< User-defined log type 1. */
> diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c index
> 4320dd4..a1ddbb3 100644
> --- a/lib/librte_mbuf/rte_mbuf.c
> +++ b/lib/librte_mbuf/rte_mbuf.c
> @@ -125,6 +125,7 @@ rte_pktmbuf_init(struct rte_mempool *mp,
>  	mbuf_size = sizeof(struct rte_mbuf) + priv_size;
>  	buf_len = rte_pktmbuf_data_room_size(mp);
> 
> +	RTE_MBUF_ASSERT((priv_size & (RTE_MBUF_PRIV_ALIGN - 1)) == 0);
Using RTE_ALIGN() could be more readable?

>  	RTE_MBUF_ASSERT(mp->elt_size >= mbuf_size);
>  	RTE_MBUF_ASSERT(buf_len <= UINT16_MAX);
> 
> @@ -154,7 +155,12 @@ rte_pktmbuf_pool_create(const char *name, unsigned
> n,
>  	struct rte_pktmbuf_pool_private mbp_priv;
>  	unsigned elt_size;
> 
> -
> +	if ((priv_size & (RTE_MBUF_PRIV_ALIGN - 1)) != 0) {
Using RTE_ALIGN() could be more readable?

> +		RTE_LOG(ERR, MBUF, "mbuf priv_size=%u is not aligned\n",
> +			priv_size);
> +		rte_errno = EINVAL;
> +		return NULL;
> +	}
>  	elt_size = sizeof(struct rte_mbuf) + (unsigned)priv_size +
>  		(unsigned)data_room_size;
>  	mbp_priv.mbuf_data_room_size = data_room_size; diff --git
> a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h index
> 010b32d..c3b8c98 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -698,6 +698,9 @@ extern "C" {
> 
> RTE_PTYPE_INNER_L4_MASK))  #endif /* RTE_NEXT_ABI */
> 
> +/** Alignment constraint of mbuf private area. */ #define
> +RTE_MBUF_PRIV_ALIGN 8
> +
>  /**
>   * Get the name of a RX offload flag
>   *
> @@ -1238,7 +1241,7 @@ void rte_pktmbuf_pool_init(struct rte_mempool *mp,
> void *opaque_arg);
>   *   details.
>   * @param priv_size
>   *   Size of application private are between the rte_mbuf structure
> - *   and the data buffer.
> + *   and the data buffer. This value must be aligned to
> RTE_MBUF_PRIV_ALIGN.
>   * @param data_room_size
>   *   Size of data buffer in each mbuf, including RTE_PKTMBUF_HEADROOM.
>   * @param socket_id
> @@ -1250,7 +1253,7 @@ void rte_pktmbuf_pool_init(struct rte_mempool *mp,
> void *opaque_arg);
>   *   with rte_errno set appropriately. Possible rte_errno values include:
>   *    - E_RTE_NO_CONFIG - function could not get pointer to rte_config
> structure
>   *    - E_RTE_SECONDARY - function was called from a secondary process
> instance
> - *    - EINVAL - cache size provided is too large
> + *    - EINVAL - cache size provided is too large, or priv_size is not aligned.
>   *    - ENOSPC - the maximum number of memzones has already been
> allocated
>   *    - EEXIST - a memzone with the same name already exists
>   *    - ENOMEM - no appropriate memory area found in which to create
> memzone
> --
> 2.1.4