[dpdk-dev] [PATCH v2 02/13] mbuf: reorder fields by time of use

Liu, Jijiang jijiang.liu at intel.com
Mon Sep 15 09:11:51 CEST 2014


Hi Bruce,

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Bruce Richardson
> Sent: Thursday, September 11, 2014 9:16 PM
> To: dev at dpdk.org
> Subject: [dpdk-dev] [PATCH v2 02/13] mbuf: reorder fields by time of use
> 
> *  Reorder the fields in the mbuf so that we have fields that are used together
> side-by-side in the structure. This means that we have a contiguous block of
> 8-bytes in the mbuf which are used to reset an mbuf of descriptor rearm, and a
> block of 16-bytes of data (excluding flags) which are set on RX from the
> received packet descriptor.
> * Use dummy fields as appropriate to ensure alignment or to reserve gaps for
> later field additions.
> * Place most items which are not used by fast-path RX separately at the end of
> the structure so they can later be moved to a separate cache line.
> [The l2/l3 length fields are not moved at this stage as doing so will cause
> overflow to the next cache line].
> 
> Updated in V2:
> * Updated the KNI buffer structure to match that of new mbuf
> * Cleaned up commit message typos.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
> ---
>  .../linuxapp/eal/include/exec-env/rte_kni_common.h | 12 ++++++-----
>  lib/librte_mbuf/rte_mbuf.h                         | 25
> ++++++++++++----------
>  2 files changed, 21 insertions(+), 16 deletions(-)
> 
> diff --git a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> index 07908ac..f2b502c 100644
> --- a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> +++ b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
> @@ -108,15 +108,17 @@ struct rte_kni_fifo {
>   * Padding is necessary to assure the offsets of these fields
>   */
>  struct rte_kni_mbuf {
> -	void *pool;
>  	void *buf_addr;
> -	char pad0[16];
> -	void *next;
> +	char pad0[10];
>  	uint16_t data_off;      /**< Start address of data in segment buffer. */
> +	char pad1[4];
> +	uint16_t ol_flags;      /**< Offload features. */
> +	char pad2[8];
>  	uint16_t data_len;      /**< Amount of data in segment buffer. */
>  	uint32_t pkt_len;       /**< Total pkt len: sum of all segment data_len.
> */
> -	char pad2[4];
> -	uint16_t ol_flags;      /**< Offload features. */
> +	char pad3[8];
> +	void *pool;
> +	void *next;
>  } __attribute__((__aligned__(64)));
> 
>  /*
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h index
> 71080e5..413a5a1 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -115,16 +115,12 @@ extern "C" {
>   * The generic rte_mbuf, containing a packet mbuf.
>   */
>  struct rte_mbuf {
> -	struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */
>  	void *buf_addr;           /**< Virtual address of segment buffer. */
>  	phys_addr_t buf_physaddr; /**< Physical address of segment buffer. */
> -	uint16_t buf_len;         /**< Length of segment buffer. */
> 
> -	/* valid for any segment */
> -	struct rte_mbuf *next;    /**< Next segment of scattered packet. */
> +	/* next 8 bytes are initialised on RX descriptor rearm */
> +	uint16_t buf_len;         /**< Length of segment buffer. */
>  	uint16_t data_off;
> -	uint16_t data_len;        /**< Amount of data in segment buffer. */
> -	uint32_t pkt_len;         /**< Total pkt len: sum of all segments. */
> 
>  #ifdef RTE_MBUF_REFCNT
>  	/**
> @@ -142,14 +138,17 @@ struct rte_mbuf {
>  #else
>  	uint16_t refcnt_reserved;     /**< Do not use this field */
>  #endif
> -	uint16_t reserved;            /**< Unused field. Required for padding
> */
> -	uint16_t ol_flags;            /**< Offload features. */
> -
> -	/* these fields are valid for first segment only */
>  	uint8_t nb_segs;        /**< Number of segments. */
>  	uint8_t port;           /**< Input port. */
> 
> -	/* offload features, valid for first segment only */
> +	uint16_t ol_flags;      /**< Offload features. */
> +	uint16_t reserved0;     /**< Unused field. Required for padding */
> +	uint32_t reserved1;     /**< Unused field. Required for padding */
> +
> +	/* remaining bytes are set on RX when pulling packet from descriptor */
> +	uint16_t reserved2;     /**< Unused field. Required for padding */
> +	uint16_t data_len;      /**< Amount of data in segment buffer. */
> +	uint32_t pkt_len;       /**< Total pkt len: sum of all segments. */
>  	union {
>  		uint16_t l2_l3_len; /**< combined l2/l3 lengths as single var */
>  		struct {
> @@ -167,6 +166,10 @@ struct rte_mbuf {
>  		uint32_t sched;     /**< Hierarchical scheduler */
>  	} hash;                 /**< hash information */
> 
> +	/* fields only used in slow path or on TX */
> +	struct rte_mempool *pool; /**< Pool from which mbuf was allocated. */
> +	struct rte_mbuf *next;    /**< Next segment of scattered packet. */
> +
>  	union {
>  		uint8_t metadata[0];
>  		uint16_t metadata16[0];
> --
> 1.9.3

It seems that you removed the inner_l3_len and inner_l2_len fields from the rte_mbuf.h structure, what is the reason?

/Jijiang Liu 


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