Re: [dpdk-dev] [PATCH v3 15/21] vhost: packed queue enqueue path

[Jens Freimann <jfreimann@redhat.com>]

On Fri, Apr 06, 2018 at 11:36:03AM +0200, Maxime Coquelin wrote:
>
>
>On 04/05/2018 12:10 PM, Jens Freimann wrote:
>>Implement enqueue of packets to the receive virtqueue.
>>
>>Set descriptor flag VIRTQ_DESC_F_USED and toggle used wrap counter if
>>last descriptor in ring is used. Perform a write memory barrier before
>>flags are written to descriptor.
>>
>>Chained descriptors are not supported with this patch.
>>
>>Signed-off-by: Jens Freimann <jfreimann@redhat.com>
>>---
>>  lib/librte_vhost/virtio_net.c | 129 ++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 129 insertions(+)
>>
>>diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
>>index 7eea1da04..578e5612e 100644
>>--- a/lib/librte_vhost/virtio_net.c
>>+++ b/lib/librte_vhost/virtio_net.c
>>@@ -695,6 +695,135 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t queue_id,
>>  	return pkt_idx;
>>  }
>>+static inline uint32_t __attribute__((always_inline))
>>+vhost_enqueue_burst_packed(struct virtio_net *dev, uint16_t queue_id,
>>+	      struct rte_mbuf **pkts, uint32_t count)
>>+{
>>+	struct vhost_virtqueue *vq;
>>+	struct vring_desc_packed *descs;
>>+	uint16_t idx;
>>+	uint16_t mask;
>>+	uint16_t i;
>>+
>>+	vq = dev->virtqueue[queue_id];
>>+
>>+	rte_spinlock_lock(&vq->access_lock);
>>+
>>+	if (unlikely(vq->enabled == 0)) {
>>+		i = 0;
>>+		goto out_access_unlock;
>>+	}
>>+
>>+	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
>>+		vhost_user_iotlb_rd_lock(vq);
>>+
>>+	descs = vq->desc_packed;
>>+	mask = vq->size - 1;
>>+
>>+	for (i = 0; i < count; i++) {
>>+		uint32_t desc_avail, desc_offset;
>>+		uint32_t mbuf_avail, mbuf_offset;
>>+		uint32_t cpy_len;
>>+		struct vring_desc_packed *desc;
>>+		uint64_t desc_addr;
>>+		struct virtio_net_hdr_mrg_rxbuf *hdr;
>>+		struct rte_mbuf *m = pkts[i];
>>+
>>+		/* XXX: there is an assumption that no desc will be chained */
>Is this assumption still true?
>If not what are the plan to fix this?

This is a leftover from the prototype code. I checked the code and
don't see what it could still relate to except if it is supposed to
mean indirect instead of chained. I think the comment can be removed. 
>
>>+		idx = vq->last_used_idx & mask;
>>+		desc = &descs[idx];
>>+
>>+		if (!desc_is_avail(vq, desc))
>IIUC, it means the ring is full.
>I think this is an unlikely case, so maybe better to use the unlikely
>macro here.

yes, we can use unlikely here, will fix.

thanks!

regards,
Jens