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From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: Joyce Kong <joyce.kong@arm.com>,
	chenbo.xia@intel.com, honnappa.nagarahalli@arm.com,
	ruifeng.wang@arm.com
Cc: dev@dpdk.org, nd@arm.com
Subject: Re: [dpdk-dev] [PATCH v1 2/8] examples/vhost_blk: replace smp with thread fence
Date: Thu, 7 Jan 2021 17:35:35 +0100
Message-ID: <69c1223d-8336-deb3-addd-2eed27e684f1@redhat.com> (raw)
In-Reply-To: <20201221155033.6771-3-joyce.kong@arm.com>



On 12/21/20 4:50 PM, Joyce Kong wrote:
> Simply replace the rte_smp_mb barriers with SEQ_CST atomic thread fence,
> if there is no load/store operations.
> 
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> ---
>  examples/vhost_blk/vhost_blk.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/examples/vhost_blk/vhost_blk.c b/examples/vhost_blk/vhost_blk.c
> index bb293d492..7ea60863d 100644
> --- a/examples/vhost_blk/vhost_blk.c
> +++ b/examples/vhost_blk/vhost_blk.c
> @@ -86,9 +86,9 @@ enqueue_task(struct vhost_blk_task *task)
>  	 */
>  	used->ring[used->idx & (vq->vring.size - 1)].id = task->req_idx;
>  	used->ring[used->idx & (vq->vring.size - 1)].len = task->data_len;

From here
> -	rte_smp_mb();
> +	rte_atomic_thread_fence(__ATOMIC_SEQ_CST);
>  	used->idx++;
> -	rte_smp_mb();
> +	rte_atomic_thread_fence(__ATOMIC_SEQ_CST);

to here, couldn't it be replaced with:
__atomic_add_fetch(&used->idx, 1, __ATOMIC_RELEASE);

?

>  	rte_vhost_clr_inflight_desc_split(task->ctrlr->vid,
>  		vq->id, used->idx, task->req_idx);
> @@ -112,12 +112,12 @@ enqueue_task_packed(struct vhost_blk_task *task)
>  	desc->id = task->buffer_id;
>  	desc->addr = 0;
>  
> -	rte_smp_mb();
> +	rte_atomic_thread_fence(__ATOMIC_SEQ_CST);
>  	if (vq->used_wrap_counter)
>  		desc->flags |= VIRTQ_DESC_F_AVAIL | VIRTQ_DESC_F_USED;
>  	else
>  		desc->flags &= ~(VIRTQ_DESC_F_AVAIL | VIRTQ_DESC_F_USED);
> -	rte_smp_mb();
> +	rte_atomic_thread_fence(__ATOMIC_SEQ_CST);
>  
>  	rte_vhost_clr_inflight_desc_packed(task->ctrlr->vid, vq->id,
>  					   task->inflight_idx);
> 


  reply	other threads:[~2021-01-07 16:35 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-21 15:50 [dpdk-dev] [PATCH v1 0/8] replace smp barriers in vhost with C11 atomic Joyce Kong
2020-12-21 15:50 ` [dpdk-dev] [PATCH v1 1/8] examples/vhost: relax memory ordering when enqueue/dequeue Joyce Kong
2021-01-07 16:33   ` Maxime Coquelin
2020-12-21 15:50 ` [dpdk-dev] [PATCH v1 2/8] examples/vhost_blk: replace smp with thread fence Joyce Kong
2021-01-07 16:35   ` Maxime Coquelin [this message]
2020-12-21 15:50 ` [dpdk-dev] [PATCH v1 3/8] vhost: remove unnecessary smp barrier for desc flags Joyce Kong
2021-01-07 16:38   ` Maxime Coquelin
2020-12-21 15:50 ` [dpdk-dev] [PATCH v1 4/8] vhost: remove unnecessary smp barrier for avail idx Joyce Kong
2021-01-07 16:43   ` Maxime Coquelin
2020-12-21 15:50 ` [dpdk-dev] [PATCH v1 5/8] vhost: relax full barriers for desc flags Joyce Kong
2021-01-07 16:45   ` Maxime Coquelin
2020-12-21 15:50 ` [dpdk-dev] [PATCH v1 6/8] vhost: relax full barriers for used idx Joyce Kong
2021-01-07 16:46   ` Maxime Coquelin
2020-12-21 15:50 ` [dpdk-dev] [PATCH v1 7/8] vhost: replace smp with thread fence for packed vring Joyce Kong
2021-01-07 17:06   ` Maxime Coquelin
2020-12-21 15:50 ` [dpdk-dev] [PATCH v1 8/8] vhost: replace smp with thread fence for control path Joyce Kong
2021-01-07 17:15   ` Maxime Coquelin
2021-01-08  9:16 ` [dpdk-dev] [PATCH v1 0/8] replace smp barriers in vhost with C11 atomic Maxime Coquelin

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