Re: [dpdk-dev] [PATCH v6 07/15] vhost: extract split ring handling from Rx and Tx functions

[Tiwei Bie <tiwei.bie@intel.com>]

On Mon, Jul 02, 2018 at 10:16:21AM +0200, Maxime Coquelin wrote:
[...]
> +
> +	if (unlikely(vq->access_ok == 0))
> +		if (unlikely(vring_translate(dev, vq) < 0))
> +			goto out;
> +
> +

Please just keep one blank line.

> +	/*
> +	 * Construct a RARP broadcast packet, and inject it to the "pkts"
> +	 * array, to looks like that guest actually send such packet.
> +	 *
> +	 * Check user_send_rarp() for more information.
> +	 *
> +	 * broadcast_rarp shares a cacheline in the virtio_net structure
> +	 * with some fields that are accessed during enqueue and
> +	 * rte_atomic16_cmpset() causes a write if using cmpxchg. This could
> +	 * result in false sharing between enqueue and dequeue.
> +	 *
> +	 * Prevent unnecessary false sharing by reading broadcast_rarp first
> +	 * and only performing cmpset if the read indicates it is likely to
> +	 * be set.
> +	 */
> +

Please remove above blank line.

> +	if (unlikely(rte_atomic16_read(&dev->broadcast_rarp) &&
> +			rte_atomic16_cmpset((volatile uint16_t *)
> +				&dev->broadcast_rarp.cnt, 1, 0))) {
> +
> +		rarp_mbuf = rte_net_make_rarp_packet(mbuf_pool, &dev->mac);
> +		if (rarp_mbuf == NULL) {
> +			RTE_LOG(ERR, VHOST_DATA,
> +				"Failed to make RARP packet.\n");
> +			return 0;
> +		}
> +		count -= 1;
> +	}
> +
> +	count = virtio_dev_tx_split(dev, vq, mbuf_pool, pkts, count);
> +
>  out:
>  	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
>  		vhost_user_iotlb_rd_unlock(vq);
> @@ -1200,10 +1222,10 @@ rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
>  		 * Inject it to the head of "pkts" array, so that switch's mac
>  		 * learning table will get updated first.
>  		 */
> -		memmove(&pkts[1], pkts, i * sizeof(struct rte_mbuf *));
> +		memmove(&pkts[1], pkts, count * sizeof(struct rte_mbuf *));
>  		pkts[0] = rarp_mbuf;
> -		i += 1;
> +		count += 1;
>  	}
>  
> -	return i;
> +	return count;
>  }
> -- 
> 2.14.4
>