Re: [dpdk-dev] [PATCH v2 3/3] net/virtio: improve batching in mergeable path

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 12/19/18 12:18 PM, Tiwei Bie wrote:
> On Tue, Dec 11, 2018 at 02:48:04PM +0100, Maxime Coquelin wrote:
>> This patch improves both descriptors dequeue and refill,
>> by using the same bathing strategy as done in in-order path.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>   drivers/net/virtio/virtio_rxtx.c | 237 ++++++++++++++++---------------
>>   1 file changed, 126 insertions(+), 111 deletions(-)
>>
>> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
>> index ebe5c74b5..59bcac2f7 100644
>> --- a/drivers/net/virtio/virtio_rxtx.c
>> +++ b/drivers/net/virtio/virtio_rxtx.c
>> @@ -267,41 +267,42 @@ virtqueue_enqueue_refill_inorder(struct virtqueue *vq,
>>   }
>>   
>>   static inline int
>> -virtqueue_enqueue_recv_refill(struct virtqueue *vq, struct rte_mbuf *cookie)
>> +virtqueue_enqueue_recv_refill(struct virtqueue *vq, struct rte_mbuf **cookie,
>> +				uint16_t num)
>>   {
>>   	struct vq_desc_extra *dxp;
>>   	struct virtio_hw *hw = vq->hw;
>> -	struct vring_desc *start_dp;
>> -	uint16_t needed = 1;
>> -	uint16_t head_idx, idx;
>> +	struct vring_desc *start_dp = vq->vq_ring.desc;
>> +	uint16_t idx, i;
>>   
>>   	if (unlikely(vq->vq_free_cnt == 0))
>>   		return -ENOSPC;
>> -	if (unlikely(vq->vq_free_cnt < needed))
>> +	if (unlikely(vq->vq_free_cnt < num))
>>   		return -EMSGSIZE;
>>   
>> -	head_idx = vq->vq_desc_head_idx;
>> -	if (unlikely(head_idx >= vq->vq_nentries))
>> +	if (unlikely(vq->vq_desc_head_idx >= vq->vq_nentries))
>>   		return -EFAULT;
>>   
>> -	idx = head_idx;
>> -	dxp = &vq->vq_descx[idx];
>> -	dxp->cookie = (void *)cookie;
>> -	dxp->ndescs = needed;
>> +	for (i = 0; i < num; i++) {
>> +		idx = vq->vq_desc_head_idx;
>> +		dxp = &vq->vq_descx[idx];
>> +		dxp->cookie = (void *)cookie[i];
>> +		dxp->ndescs = 1;
>>   
>> -	start_dp = vq->vq_ring.desc;
>> -	start_dp[idx].addr =
>> -		VIRTIO_MBUF_ADDR(cookie, vq) +
>> -		RTE_PKTMBUF_HEADROOM - hw->vtnet_hdr_size;
>> -	start_dp[idx].len =
>> -		cookie->buf_len - RTE_PKTMBUF_HEADROOM + hw->vtnet_hdr_size;
>> -	start_dp[idx].flags =  VRING_DESC_F_WRITE;
>> -	idx = start_dp[idx].next;
>> -	vq->vq_desc_head_idx = idx;
>> -	if (vq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END)
>> -		vq->vq_desc_tail_idx = idx;
>> -	vq->vq_free_cnt = (uint16_t)(vq->vq_free_cnt - needed);
>> -	vq_update_avail_ring(vq, head_idx);
>> +		start_dp[idx].addr =
>> +			VIRTIO_MBUF_ADDR(cookie[i], vq) +
>> +			RTE_PKTMBUF_HEADROOM - hw->vtnet_hdr_size;
>> +		start_dp[idx].len =
>> +			cookie[i]->buf_len - RTE_PKTMBUF_HEADROOM +
>> +			hw->vtnet_hdr_size;
>> +		start_dp[idx].flags = VRING_DESC_F_WRITE;
>> +		vq->vq_desc_head_idx = start_dp[idx].next;
>> +		if (vq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END)
>> +			vq->vq_desc_tail_idx = vq->vq_desc_head_idx;
> 
> It's better to break the loop here. Or maybe move
> this check out of the loop.

Right, I vote for breaking, else we might get an out of bound access.

Thanks!

>> +		vq_update_avail_ring(vq, idx);
>> +	}
>> +
>> +	vq->vq_free_cnt = (uint16_t)(vq->vq_free_cnt - num);
>>   
>>   	return 0;
>>   }
> [...]
>