[dpdk-dev] [PATCH] ring: fix sc dequeue performance issue

[Ananyev, Konstantin]

> -----Original Message-----
> From: Jerin Jacob [mailto:jerin.jacob at caviumnetworks.com]
> Sent: Sunday, July 24, 2016 6:08 PM
> To: dev at dpdk.org
> Cc: thomas.monjalon at 6wind.com; Ananyev, Konstantin <konstantin.ananyev at intel.com>; Jerin Jacob
> <jerin.jacob at caviumnetworks.com>
> Subject: [dpdk-dev] [PATCH] ring: fix sc dequeue performance issue
> 
> Use of rte_smb_wmb() instead of rte_smb_rmb() in sc dequeue function creates the additional overhead of waiting for all the STOREs to be
> completed to local buffer from ring buffer memory. The sc dequeue function demands only LOAD-STORE barrier where LOADs from ring
> buffer memory needs to be completed before tail pointer update. Changing to rte_smb_rmb() to enable the required LOAD-STORE barrier.
> 
> Fixes: ecc7d10e448e ("ring: guarantee dequeue ordering before tail update")
> 
> Signed-off-by: Jerin Jacob <jerin.jacob at caviumnetworks.com>
> ---
>  lib/librte_ring/rte_ring.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h index f928324..0e22e69 100644
> --- a/lib/librte_ring/rte_ring.h
> +++ b/lib/librte_ring/rte_ring.h
> @@ -756,7 +756,7 @@ __rte_ring_sc_do_dequeue(struct rte_ring *r, void **obj_table,
> 
>  	/* copy in table */
>  	DEQUEUE_PTRS();
> -	rte_smp_wmb();
> +	rte_smp_rmb();
> 
>  	__RING_STAT_ADD(r, deq_success, n);
>  	r->cons.tail = cons_next;
> --

Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com>

> 2.5.5