Re: [dpdk-dev] [PATCH] ixgbe: fix compile error with gcc4.4 (used RHEL 6)

[Thomas Monjalon <thomas.monjalon@6wind.com>]

Hi Neil,

2014-09-18 11:03, Neil Horman:
> Thank you, I've reproduced the problem here, and you're right, it is a
> compiler bug, but I really hate the idea of just throwing braces around
> something to shut the compiler up, especially when the compiler has since
> been fixed.  Looking at it a bit more closely it seems like the the thing
> to do is actually just consistently use rte_mbuf_refcnt_set, since thats
> what the rte_mbuf header documentation says to do, and protects you if the
> internal structure changes, as well as prevents you from having to spread
> ifdef RTE_MBUF_REFCNT all over the place.
> 
> This patch does a bit more than that too.  With a little creative
> typedef-ing we don't need the anonymous union at all, and lets us just use
> a single refcnt variable, and I think eliminate that odd refcnt_reserved
> member of the union, that, as far as I can see, does nothing.

> --- a/config/common_linuxapp
> +++ b/config/common_linuxapp
> @@ -123,7 +123,7 @@ CONFIG_RTE_LOG_HISTORY=256
>  CONFIG_RTE_LIBEAL_USE_HPET=n
>  CONFIG_RTE_EAL_ALLOW_INV_SOCKET_ID=n
>  CONFIG_RTE_EAL_ALWAYS_PANIC_ON_ERROR=n
> -CONFIG_RTE_EAL_IGB_UIO=y
> +CONFIG_RTE_EAL_IGB_UIO=n
>  CONFIG_RTE_EAL_VFIO=y

Hum, indeed this patch does a bit more ;)

[...]
> -CONFIG_RTE_LIBRTE_KNI=y
> +CONFIG_RTE_LIBRTE_KNI=n
>  CONFIG_RTE_KNI_KO_DEBUG=n

> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -120,6 +120,15 @@ extern "C" {
>  typedef void    *MARKER[0];   /**< generic marker for a point in a
> structure */ typedef uint64_t MARKER64[0]; /**< marker that allows us to
> overwrite 8 bytes * with a single assignment */
> +
> +#ifdef RTE_MBUF_REFCNT
> +#ifdef RTE_MBUF_REFCNT_ATOMIC
> +typedef rte_atomic16_t rte_refcnt;
> +#else
> +typedef uint16_t rte_refcnt;
> +#endif
> +#endif
> +
>  /**
>   * The generic rte_mbuf, containing a packet mbuf.
>   */
> @@ -142,13 +151,9 @@ struct rte_mbuf {
>  	 * or non-atomic) is controlled by the CONFIG_RTE_MBUF_REFCNT_ATOMIC
>  	 * config option.
>  	 */
> -	union {
>  #ifdef RTE_MBUF_REFCNT
> -		rte_atomic16_t refcnt_atomic; /**< Atomically accessed refcnt */
> -		uint16_t refcnt;              /**< Non-atomically accessed refcnt */
> +	rte_refcnt refcnt;
>  #endif
> -		uint16_t refcnt_reserved;     /**< Do not use this field */
> -	};

You are changing the mbuf alignment if MBUF_REFCNT is disabled.

> --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> @@ -722,11 +722,9 @@ ixgbe_rxq_vec_setup(struct igb_rx_queue *rxq)
>  	static struct rte_mbuf mb_def = {
>  		.nb_segs = 1,
>  		.data_off = RTE_PKTMBUF_HEADROOM,
> -#ifdef RTE_MBUF_REFCNT
> -		{ .refcnt = 1, }
> -#endif
>  	};
> 
> +	rte_mbuf_refcnt_set(&mb_def, 1);

Performance impact must be checked here.

-- 
Thomas