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

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

On 07/30/2015 05:33 PM, Zhang, Helin wrote:
>
>
>> -----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?

Will do, thanks for commenting.



>
>> +		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
>