Re: [dpdk-dev] [PATCH 1/2] lib/ethdev: replace full barrier with relaxed barrier

[Ferruh Yigit <ferruh.yigit@intel.com>]

On 10/2/2020 1:07 AM, Honnappa Nagarahalli wrote:
> From: Phil Yang <phil.yang@arm.com>
> 
> While registering the call back functions full write barrier
> can be replaced with one-way write barrier.
> 
> Signed-off-by: Phil Yang <phil.yang@arm.com>
> Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>

+Konstantin & Jerin,

Can you please help reviewing this patch?

> ---
>   lib/librte_ethdev/rte_ethdev.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
> index 7858ad5f1..59a41c07f 100644
> --- a/lib/librte_ethdev/rte_ethdev.c
> +++ b/lib/librte_ethdev/rte_ethdev.c
> @@ -26,7 +26,6 @@
>   #include <rte_eal.h>
>   #include <rte_per_lcore.h>
>   #include <rte_lcore.h>
> -#include <rte_atomic.h>
>   #include <rte_branch_prediction.h>
>   #include <rte_common.h>
>   #include <rte_mempool.h>
> @@ -4527,8 +4526,12 @@ rte_eth_add_first_rx_callback(uint16_t port_id, uint16_t queue_id,
>   	rte_spinlock_lock(&rte_eth_rx_cb_lock);
>   	/* Add the callbacks at first position */
>   	cb->next = rte_eth_devices[port_id].post_rx_burst_cbs[queue_id];
> -	rte_smp_wmb();
> -	rte_eth_devices[port_id].post_rx_burst_cbs[queue_id] = cb;
> +	/* Stores to cb->fn, cb->param and cb->next should complete before
> +	 * cb is visible to data plane threads.
> +	 */
> +	__atomic_store_n(
> +		&rte_eth_devices[port_id].post_rx_burst_cbs[queue_id],
> +		cb, __ATOMIC_RELEASE);
>   	rte_spinlock_unlock(&rte_eth_rx_cb_lock);
>   
>   	return cb;
>