Re: [dpdk-dev] [PATCH] ethdev: make struct rte_eth_dev cache aligned

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, May 02, 2016 at 01:37:45PM +0530, Jerin Jacob wrote:
> Elements of struct rte_eth_dev used in the fast path.
> Make struct rte_eth_dev cache aligned to avoid the cases where
> rte_eth_dev elements share the same cache line with other structures.
> 
> Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> ---
>  lib/librte_ether/rte_ethdev.c | 2 +-
>  lib/librte_ether/rte_ethdev.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/librte_ether/rte_ethdev.c b/lib/librte_ether/rte_ethdev.c
> index a31018e..04f492d 100644
> --- a/lib/librte_ether/rte_ethdev.c
> +++ b/lib/librte_ether/rte_ethdev.c
> @@ -70,7 +70,7 @@
>  #include "rte_ethdev.h"
>  
>  static const char *MZ_RTE_ETH_DEV_DATA = "rte_eth_dev_data";
> -struct rte_eth_dev rte_eth_devices[RTE_MAX_ETHPORTS];
> +struct rte_eth_dev rte_eth_devices[RTE_MAX_ETHPORTS] __rte_cache_aligned;
>  static struct rte_eth_dev_data *rte_eth_dev_data;
>  static uint8_t nb_ports;
>  
> diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
> index 8519ff6..e359dda 100644
> --- a/lib/librte_ether/rte_ethdev.h
> +++ b/lib/librte_ether/rte_ethdev.h
> @@ -1630,7 +1630,7 @@ struct rte_eth_dev {
>  	struct rte_eth_rxtx_callback *pre_tx_burst_cbs[RTE_MAX_QUEUES_PER_PORT];
>  	uint8_t attached; /**< Flag indicating the port is attached */
>  	enum rte_eth_dev_type dev_type; /**< Flag indicating the device type */
> -};
> +} __rte_cache_aligned;
>  
>  struct rte_eth_dev_sriov {
>  	uint8_t active;               /**< SRIOV is active with 16, 32 or 64 pools */
> -- 
Adding cache aligned in two places is overkill, I think. If the structure is
marked as being cache aligned, there is no need to have the rte_eth_devices
marked that way too. I suggest therefore just keeping the structure alignment.

Regards,
/Bruce