[dpdk-dev] [PATCH 5/5] net/virtio: optimize xmit enqueue for packed ring

Maxime Coquelin maxime.coquelin at redhat.com
Thu Feb 21 13:31:58 CET 2019



On 2/21/19 1:25 PM, Tiwei Bie wrote:
> On Thu, Feb 21, 2019 at 12:22:29PM +0100, Maxime Coquelin wrote:
>> On 2/19/19 11:59 AM, Tiwei Bie wrote:
>>> This patch introduces an optimized enqueue function in packed
>>> ring for the case that virtio net header can be prepended to
>>> the unchained mbuf.
>>>
>>> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
>>> ---
>>>    drivers/net/virtio/virtio_rxtx.c | 63 +++++++++++++++++++++++++++++++-
>>>    1 file changed, 61 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
>>> index 60fa3aa50..771d3c3f6 100644
>>> --- a/drivers/net/virtio/virtio_rxtx.c
>>> +++ b/drivers/net/virtio/virtio_rxtx.c
>>> @@ -623,6 +623,62 @@ virtqueue_enqueue_xmit_inorder(struct virtnet_tx *txvq,
>>>    	vq->vq_desc_head_idx = idx & (vq->vq_nentries - 1);
>>>    }
>>> +static inline void
>>> +virtqueue_enqueue_xmit_packed_fast(struct virtnet_tx *txvq,
>>> +				   struct rte_mbuf *cookie,
>>> +				   int in_order)
>>> +{
>>> +	struct virtqueue *vq = txvq->vq;
>>> +	struct vring_packed_desc *dp;
>>> +	struct vq_desc_extra *dxp;
>>> +	uint16_t idx, id, flags;
>>> +	uint16_t head_size = vq->hw->vtnet_hdr_size;
>>> +	struct virtio_net_hdr *hdr;
>>> +
>>> +	id = in_order ? vq->vq_avail_idx : vq->vq_desc_head_idx;
>>> +	idx = vq->vq_avail_idx;
>>> +	dp = &vq->ring_packed.desc_packed[idx];
>>> +
>>> +	dxp = &vq->vq_descx[id];
>>> +	dxp->ndescs = 1;
>>> +	dxp->cookie = cookie;
>>> +
>>> +	flags = vq->avail_used_flags;
>>> +
>>> +	/* prepend cannot fail, checked by caller */
>>> +	hdr = (struct virtio_net_hdr *)
>>> +		rte_pktmbuf_prepend(cookie, head_size);
>>> +	cookie->pkt_len -= head_size;
>>> +
>>> +	/* if offload disabled, hdr is not zeroed yet, do it now */
>>> +	if (!vq->hw->has_tx_offload)
>>> +		virtqueue_clear_net_hdr(hdr);
>>> +	else
>>> +		virtqueue_xmit_offload(hdr, cookie, true);
>>> +
>>> +	dp->addr = VIRTIO_MBUF_DATA_DMA_ADDR(cookie, vq);
>>> +	dp->len  = cookie->data_len;
>>> +	dp->id   = id;
>>> +
>>> +	if (++vq->vq_avail_idx >= vq->vq_nentries) {
>>> +		vq->vq_avail_idx -= vq->vq_nentries;
>>> +		vq->avail_wrap_counter ^= 1;
>>> +		vq->avail_used_flags ^=
>>> +			VRING_DESC_F_AVAIL(1) | VRING_DESC_F_USED(1);
>>> +	}
>>> +
>>> +	vq->vq_free_cnt--;
>>> +
>>> +	if (!in_order) {
>>> +		vq->vq_desc_head_idx = dxp->next;
>>> +		if (vq->vq_desc_head_idx == VQ_RING_DESC_CHAIN_END)
>>> +			vq->vq_desc_tail_idx = VQ_RING_DESC_CHAIN_END;
>>> +	}
>>> +
>>> +	virtio_wmb(vq->hw->weak_barriers);
>>> +	dp->flags = flags;
>>> +}
>>> +
>>>    static inline void
>>>    virtqueue_enqueue_xmit_packed(struct virtnet_tx *txvq, struct rte_mbuf *cookie,
>>>    			      uint16_t needed, int can_push, int in_order)
>>> @@ -1979,8 +2035,11 @@ virtio_xmit_pkts_packed(void *tx_queue, struct rte_mbuf **tx_pkts,
>>>    		}
>>>    		/* Enqueue Packet buffers */
>>> -		virtqueue_enqueue_xmit_packed(txvq, txm, slots, can_push,
>>> -					      in_order);
>>> +		if (can_push)
>>> +			virtqueue_enqueue_xmit_packed_fast(txvq, txm, in_order);
>>> +		else
>>> +			virtqueue_enqueue_xmit_packed(txvq, txm, slots, 0,
>>> +						      in_order);
>>>    		virtio_update_packet_stats(&txvq->stats, txm);
>>>    	}
>>>
>>
>> I like this patch, but shouldn't virtqueue_enqueue_xmit_packed() be
>> simplified to get rid off "can_push" now that this case as a dedicated
>> function?
> 
> Yeah, I had the same thought. But after a second thought, I
> think we may also want to push the net hdr to the mbuf even
> if its nb_segs isn't 1 in the future, so I left it untouched.

Ok, that makes sense.
And I think doing the change won't affect the generated code much
anyway, as "can_push" related things will be stripped out at compilation 
time.

Reviewed-by: Maxime Coquelin <maxime.coquelin at redhat.com>

Thanks,
Maxime

> Thanks,
> Tiwei
> 


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