[dpdk-dev] [PATCH v2 08/16] vhost: add flush function for burst enqueue

[Liu, Yong]

> -----Original Message-----
> From: Gavin Hu (Arm Technology China) [mailto:Gavin.Hu at arm.com]
> Sent: Wednesday, September 25, 2019 11:38 AM
> To: Liu, Yong <yong.liu at intel.com>; maxime.coquelin at redhat.com; Bie, Tiwei
> <tiwei.bie at intel.com>; Wang, Zhihong <zhihong.wang at intel.com>
> Cc: dev at dpdk.org; nd <nd at arm.com>
> Subject: RE: [dpdk-dev] [PATCH v2 08/16] vhost: add flush function for
> burst enqueue
> 
> Hi Marvin,
> 
> One typo and one comment about the barrier.
> 
> /Gavin
> 
> > -----Original Message-----
> > From: dev <dev-bounces at dpdk.org> On Behalf Of Marvin Liu
> > Sent: Friday, September 20, 2019 12:37 AM
> > To: maxime.coquelin at redhat.com; tiwei.bie at intel.com;
> > zhihong.wang at intel.com
> > Cc: dev at dpdk.org; Marvin Liu <yong.liu at intel.com>
> > Subject: [dpdk-dev] [PATCH v2 08/16] vhost: add flush function for burst
> > enqueue
> >
> > Flush used flags when burst enqueue function is finished. Descriptor's
> > flags are pre-calculated as them will be reset by vhost.
> s/them/they
> 

Thanks.

> >
> > Signed-off-by: Marvin Liu <yong.liu at intel.com>
> >
> > diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> > index 000648dd4..9c42c7db0 100644
> > --- a/lib/librte_vhost/vhost.h
> > +++ b/lib/librte_vhost/vhost.h
> > @@ -39,6 +39,9 @@
> >
> >  #define VHOST_LOG_CACHE_NR 32
> >
> > +#define VIRTIO_RX_USED_FLAG  (0ULL | VRING_DESC_F_AVAIL |
> > VRING_DESC_F_USED \
> > +				| VRING_DESC_F_WRITE)
> > +#define VIRTIO_RX_USED_WRAP_FLAG (VRING_DESC_F_WRITE)
> >  #define PACKED_DESCS_BURST (RTE_CACHE_LINE_SIZE / \
> >  			    sizeof(struct vring_packed_desc))
> >
> > diff --git a/lib/librte_vhost/virtio_net.c
> b/lib/librte_vhost/virtio_net.c
> > index e2787b72e..8e4036204 100644
> > --- a/lib/librte_vhost/virtio_net.c
> > +++ b/lib/librte_vhost/virtio_net.c
> > @@ -169,6 +169,51 @@ update_shadow_packed(struct vhost_virtqueue
> > *vq,
> >  	vq->shadow_used_packed[i].count = count;
> >  }
> >
> > +static __rte_always_inline void
> > +flush_burst_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
> > +	uint64_t *lens, uint16_t *ids, uint16_t flags)
> > +{
> > +	uint16_t i;
> > +
> > +	UNROLL_PRAGMA(PRAGMA_PARAM)
> > +	for (i = 0; i < PACKED_DESCS_BURST; i++) {
> > +		vq->desc_packed[vq->last_used_idx + i].id = ids[i];
> > +		vq->desc_packed[vq->last_used_idx + i].len = lens[i];
> > +	}
> > +
> > +	UNROLL_PRAGMA(PRAGMA_PARAM)
> > +	for (i = 0; i < PACKED_DESCS_BURST; i++) {
> > +		rte_smp_wmb();
> Should this rte_smp_wmb() be moved above the loop? It guarantees the
> orderings of updates of id, len happens before the flags,
> But all the flags of different descriptors should not be ordered.
> 
Hi Gavin,
For each descriptor, virtio driver will first check flags and then check read barrier, at the last driver will read id and length.
So wmb here is to guarantee that id and length are updated before flags. And afterwards wmb is to guarantee the sequence.

Thanks,
Marvin

> > +		vq->desc_packed[vq->last_used_idx + i].flags = flags;
> > +	}
> > +
> > +	vhost_log_cache_used_vring(dev, vq, vq->last_used_idx *
> > +				   sizeof(struct vring_packed_desc),
> > +				   sizeof(struct vring_packed_desc) *
> > +				   PACKED_DESCS_BURST);
> > +	vhost_log_cache_sync(dev, vq);
> > +
> > +	vq->last_used_idx += PACKED_DESCS_BURST;
> > +	if (vq->last_used_idx >= vq->size) {
> > +		vq->used_wrap_counter ^= 1;
> > +		vq->last_used_idx -= vq->size;
> > +	}
> > +}
> > +
> > +static __rte_always_inline void
> > +flush_enqueue_burst_packed(struct virtio_net *dev, struct
> > vhost_virtqueue *vq,
> > +	uint64_t *lens, uint16_t *ids)
> > +{
> > +	uint16_t flags = 0;
> > +
> > +	if (vq->used_wrap_counter)
> > +		flags = VIRTIO_RX_USED_FLAG;
> > +	else
> > +		flags = VIRTIO_RX_USED_WRAP_FLAG;
> > +
> > +	flush_burst_packed(dev, vq, lens, ids, flags);
> > +}
> > +
> >  static __rte_always_inline void
> >  update_enqueue_shadow_packed(struct vhost_virtqueue *vq, uint16_t
> > desc_idx,
> >  	uint32_t len, uint16_t count)
> > @@ -950,6 +995,7 @@ virtio_dev_rx_burst_packed(struct virtio_net *dev,
> > struct vhost_virtqueue *vq,
> >  	struct virtio_net_hdr_mrg_rxbuf *hdrs[PACKED_DESCS_BURST];
> >  	uint32_t buf_offset = dev->vhost_hlen;
> >  	uint64_t lens[PACKED_DESCS_BURST];
> > +	uint16_t ids[PACKED_DESCS_BURST];
> >
> >  	uint16_t i;
> >
> > @@ -1013,6 +1059,12 @@ virtio_dev_rx_burst_packed(struct virtio_net
> > *dev, struct vhost_virtqueue *vq,
> >  			   pkts[i]->pkt_len);
> >  	}
> >
> > +	UNROLL_PRAGMA(PRAGMA_PARAM)
> > +	for (i = 0; i < PACKED_DESCS_BURST; i++)
> > +		ids[i] = descs[avail_idx + i].id;
> > +
> > +	flush_enqueue_burst_packed(dev, vq, lens, ids);
> > +
> >  	return 0;
> >  }
> >
> > --
> > 2.17.1