Re: [PATCH v4 2/6] vhost: rewrite enqueue

["Wang, Zhihong" <zhihong.wang@intel.com>]

> -----Original Message-----
> From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> Sent: Wednesday, September 7, 2016 1:33 PM
> To: Wang, Zhihong <zhihong.wang@intel.com>
> Cc: dev@dpdk.org; maxime.coquelin@redhat.com;
> thomas.monjalon@6wind.com
> Subject: Re: [PATCH v4 2/6] vhost: rewrite enqueue
> 
> Hmmm, yet another email didn't send out successfully. Resend.
> 
> BTW, please work out v5 on top of the latest next-virtio tree.
> 
> Thanks.

Okay. Thanks.

> 
> 	--yliu
> 
> On Mon, Sep 05, 2016 at 02:39:25PM +0800, Yuanhan Liu wrote:
> ----
> On Mon, Aug 29, 2016 at 11:36:00PM -0400, Zhihong Wang wrote:
> > This patch implements the vhost logic from scratch into a single function
> > designed for high performance and better maintainability.
> >
> > This is the baseline version of the new code, more optimization will be
> > added in the following patches in this patch set.
> >
> > ---
> > Changes in v4:
> >
> >  1. Refactor the code for clearer logic.
> >
> >  2. Add PRINT_PACKET for debugging.
> >
> > ---
> > Changes in v3:
> >
> >  1. Rewrite enqueue and delete the obsolete in the same patch.
> 
> Change log should go ---->
> 
> > Signed-off-by: Zhihong Wang <zhihong.wang@intel.com>
> > ---
> 
> ... here, after the SoB.
> 
> >  lib/librte_vhost/vhost_rxtx.c | 525 ++++++++++++-----------------------------
> -
> >  1 file changed, 145 insertions(+), 380 deletions(-)
> >
> > diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
> > index 5806f99..629e8ae 100644
> > --- a/lib/librte_vhost/vhost_rxtx.c
> > +++ b/lib/librte_vhost/vhost_rxtx.c
> > @@ -91,7 +91,7 @@ is_valid_virt_queue_idx(uint32_t idx, int is_tx,
> uint32_t qp_nb)
> >  	return (is_tx ^ (idx & 1)) == 0 && idx < qp_nb * VIRTIO_QNUM;
> >  }
> >
> > -static void
> > +static inline void __attribute__((always_inline))
> >  virtio_enqueue_offload(struct rte_mbuf *m_buf, struct virtio_net_hdr
> *net_hdr)
> >  {
> >  	if (m_buf->ol_flags & PKT_TX_L4_MASK) {
> > @@ -112,6 +112,10 @@ virtio_enqueue_offload(struct rte_mbuf *m_buf,
> struct virtio_net_hdr *net_hdr)
> >  						cksum));
> >  			break;
> >  		}
> > +	} else {
> > +		net_hdr->flags = 0;
> > +		net_hdr->csum_start = 0;
> > +		net_hdr->csum_offset = 0;
> >  	}
> >
> >  	if (m_buf->ol_flags & PKT_TX_TCP_SEG) {
> > @@ -122,437 +126,198 @@ virtio_enqueue_offload(struct rte_mbuf
> *m_buf, struct virtio_net_hdr *net_hdr)
> >  		net_hdr->gso_size = m_buf->tso_segsz;
> >  		net_hdr->hdr_len = m_buf->l2_len + m_buf->l3_len
> >  					+ m_buf->l4_len;
> > +	} else {
> > +		net_hdr->gso_type = 0;
> > +		net_hdr->hdr_len = 0;
> > +		net_hdr->gso_size = 0;
> >  	}
> >  }
> >
> > -static inline void
> > -copy_virtio_net_hdr(struct virtio_net *dev, uint64_t desc_addr,
> > -		    struct virtio_net_hdr_mrg_rxbuf hdr)
> > +static inline void __attribute__((always_inline))
> > +update_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
> > +		uint32_t desc_chain_head, uint32_t desc_chain_len)
> >  {
> > -	if (dev->vhost_hlen == sizeof(struct virtio_net_hdr_mrg_rxbuf))
> > -		*(struct virtio_net_hdr_mrg_rxbuf *)(uintptr_t)desc_addr =
> hdr;
> > -	else
> > -		*(struct virtio_net_hdr *)(uintptr_t)desc_addr = hdr.hdr;
> > +	uint32_t used_idx_round = vq->last_used_idx & (vq->size - 1);
> 
> I'd suggest to use "used_idx", instead of "used_idx_round".
> 
> > +
> > +	vq->used->ring[used_idx_round].id = desc_chain_head;
> > +	vq->used->ring[used_idx_round].len = desc_chain_len;
> > +	vhost_log_used_vring(dev, vq, offsetof(struct vring_used,
> > +				ring[used_idx_round]),
> > +			sizeof(vq->used->ring[used_idx_round]));
> >  }
> >
> > -static inline int __attribute__((always_inline))
> > -copy_mbuf_to_desc(struct virtio_net *dev, struct vhost_virtqueue *vq,
> > -		  struct rte_mbuf *m, uint16_t desc_idx)
> > +static inline uint32_t __attribute__((always_inline))
> > +enqueue_packet(struct virtio_net *dev, struct vhost_virtqueue *vq,
> > +		uint16_t avail_idx, struct rte_mbuf *mbuf,
> > +		uint32_t is_mrg_rxbuf)
> >  {
> > -	uint32_t desc_avail, desc_offset;
> > -	uint32_t mbuf_avail, mbuf_offset;
> > -	uint32_t cpy_len;
> > +	struct virtio_net_hdr_mrg_rxbuf *virtio_hdr;
> >  	struct vring_desc *desc;
> >  	uint64_t desc_addr;
> > -	struct virtio_net_hdr_mrg_rxbuf virtio_hdr = {{0, 0, 0, 0, 0, 0}, 0};
> > -
> > -	desc = &vq->desc[desc_idx];
> > +	uint32_t desc_chain_head;
> > +	uint32_t desc_chain_len;
> > +	uint32_t desc_current;
> > +	uint32_t desc_offset;
> > +	uint32_t mbuf_len;
> > +	uint32_t mbuf_avail;
> > +	uint32_t copy_len;
> > +	uint32_t extra_buffers = 0;
> 
> I'd name it to "num_buffers", to keep consistent with the virito hdr
> naming style.
> 
> > +
> > +	/* start with the first mbuf of the packet */
> > +	mbuf_len = rte_pktmbuf_data_len(mbuf);
> > +	mbuf_avail = mbuf_len;
> > +
> > +	/* get the current desc */
> > +	desc_current = vq->avail->ring[(vq->last_used_idx) & (vq->size - 1)];
> > +	desc_chain_head = desc_current;
> > +	desc = &vq->desc[desc_current];
> >  	desc_addr = gpa_to_vva(dev, desc->addr);
> > -	/*
> > -	 * Checking of 'desc_addr' placed outside of 'unlikely' macro to avoid
> > -	 * performance issue with some versions of gcc (4.8.4 and 5.3.0)
> which
> > -	 * otherwise stores offset on the stack instead of in a register.
> > -	 */
> > -	if (unlikely(desc->len < dev->vhost_hlen) || !desc_addr)
> > -		return -1;
> > +	if (unlikely(!desc_addr))
> > +		goto error;
> >
> > -	rte_prefetch0((void *)(uintptr_t)desc_addr);
> > +	/* handle virtio header */
> > +	virtio_hdr = (struct virtio_net_hdr_mrg_rxbuf
> *)(uintptr_t)desc_addr;
> > +	virtio_enqueue_offload(mbuf, &(virtio_hdr->hdr));
> > +	if (is_mrg_rxbuf)
> > +		virtio_hdr->num_buffers = extra_buffers + 1;
> >
> > -	virtio_enqueue_offload(m, &virtio_hdr.hdr);
> > -	copy_virtio_net_hdr(dev, desc_addr, virtio_hdr);
> >  	vhost_log_write(dev, desc->addr, dev->vhost_hlen);
> >  	PRINT_PACKET(dev, (uintptr_t)desc_addr, dev->vhost_hlen, 0);
> > -
> >  	desc_offset = dev->vhost_hlen;
> > -	desc_avail  = desc->len - dev->vhost_hlen;
> > -
> > -	mbuf_avail  = rte_pktmbuf_data_len(m);
> > -	mbuf_offset = 0;
> > -	while (mbuf_avail != 0 || m->next != NULL) {
> > -		/* done with current mbuf, fetch next */
> > -		if (mbuf_avail == 0) {
> > -			m = m->next;
> > -
> > -			mbuf_offset = 0;
> > -			mbuf_avail  = rte_pktmbuf_data_len(m);
> > +	desc_chain_len = desc_offset;
> > +	desc_addr += desc_offset;
> > +
> > +	/* start copy from mbuf to desc */
> > +	while (mbuf_avail || mbuf->next) {
> > +		/* get the next mbuf if the current done */
> > +		if (!mbuf_avail) {
> > +			mbuf = mbuf->next;
> > +			mbuf_len = rte_pktmbuf_data_len(mbuf);
> > +			mbuf_avail = mbuf_len;
> >  		}
> >
> > -		/* done with current desc buf, fetch next */
> > -		if (desc_avail == 0) {
> > -			if ((desc->flags & VRING_DESC_F_NEXT) == 0) {
> > -				/* Room in vring buffer is not enough */
> > -				return -1;
> > -			}
> > -			if (unlikely(desc->next >= vq->size))
> > -				return -1;
> > +		/* get the next desc if the current done */
> > +		if (desc->len <= desc_offset) {
> > +			if (desc->flags & VRING_DESC_F_NEXT) {
> > +				/* go on with the current desc chain */
> > +				desc_offset = 0;
> > +				desc_current = desc->next;
> > +				desc = &vq->desc[desc_current];
> > +				desc_addr = gpa_to_vva(dev, desc->addr);
> > +				if (unlikely(!desc_addr))
> > +					goto error;
> > +			} else if (is_mrg_rxbuf) {
> > +				/* start with the next desc chain */
> > +				update_used_ring(dev, vq,
> desc_chain_head,
> > +						desc_chain_len);
> > +				vq->last_used_idx++;
> 
> Why not putting "vq->last_used_idx++" into update_used_ring()?
> 
> > +				extra_buffers++;
> > +				virtio_hdr->num_buffers++;
> > +				if (avail_idx == vq->last_used_idx)
> > +					goto error;
> > +
> > +				desc_current =
> > +					vq->avail->ring[(vq->last_used_idx)
> &
> > +					(vq->size - 1)];
> > +				desc_chain_head = desc_current;
> > +				desc = &vq->desc[desc_current];
> > +				desc_addr = gpa_to_vva(dev, desc->addr);
> > +				if (unlikely(!desc_addr))
> > +					goto error;
> >
> > -			desc = &vq->desc[desc->next];
> > -			desc_addr = gpa_to_vva(dev, desc->addr);
> > -			if (unlikely(!desc_addr))
> > -				return -1;
> > -
> > -			desc_offset = 0;
> > -			desc_avail  = desc->len;
> > +				desc_chain_len = 0;
> > +				desc_offset = 0;
> > +			} else
> > +				goto error;
> >  		}
> >
> > -		cpy_len = RTE_MIN(desc_avail, mbuf_avail);
> > -		rte_memcpy((void *)((uintptr_t)(desc_addr + desc_offset)),
> > -			rte_pktmbuf_mtod_offset(m, void *, mbuf_offset),
> > -			cpy_len);
> > -		vhost_log_write(dev, desc->addr + desc_offset, cpy_len);
> > -		PRINT_PACKET(dev, (uintptr_t)(desc_addr + desc_offset),
> > -			     cpy_len, 0);
> > -
> > -		mbuf_avail  -= cpy_len;
> > -		mbuf_offset += cpy_len;
> > -		desc_avail  -= cpy_len;
> > -		desc_offset += cpy_len;
> > +		/* copy mbuf data */
> > +		copy_len = RTE_MIN(desc->len - desc_offset, mbuf_avail);
> 
> TBH, I'm okay with copy_len (actually, I prefer it slightly). However,
> the old code uses cpy_len, the current dequeue function also uses cpy_len,
> I then see no good reason to use copy_len here. It's really not a good
> idea to me to use two different naming styles in one source file.
> 
> 
> > +		rte_memcpy((void *)(uintptr_t)desc_addr,
> > +				rte_pktmbuf_mtod_offset(mbuf, void *,
> > +					mbuf_len - mbuf_avail),
> 
> I would keep the old var "mbuf_offset" and do not introduce "mbuf_len".
> This could avoid above calculation and make it straightforward.
> 
> > +				copy_len);
> > +		vhost_log_write(dev, desc->addr + desc_offset, copy_len);
> > +		PRINT_PACKET(dev, (uintptr_t)desc_addr, copy_len, 0);
> > +		mbuf_avail -= copy_len;
> > +		desc_offset += copy_len;
> > +		desc_addr += copy_len;
> > +		desc_chain_len += copy_len;
> 
> Vertical alighment[0] is not a must, but as you can see, it's a style I
> prefer. Meaning, if possible, please follow it.
> 
> [0]: https://en.wikipedia.org/wiki/Programming_style#Vertical_alignment
> 
> >  	}
> >
> > -	return 0;
> > -}
> > +	update_used_ring(dev, vq, desc_chain_head, desc_chain_len);
> > +	vq->last_used_idx++;
> >
> ...
> > -	rte_prefetch0(&vq->desc[desc_indexes[0]]);
> > -	for (i = 0; i < count; i++) {
> > -		uint16_t desc_idx = desc_indexes[i];
> > -		int err;
> > +	return 0;
> >
> > -		err = copy_mbuf_to_desc(dev, vq, pkts[i], desc_idx);
> > -		if (unlikely(err)) {
> > -			used_idx = (start_idx + i) & (vq->size - 1);
> > -			vq->used->ring[used_idx].len = dev->vhost_hlen;
> > -			vhost_log_used_vring(dev, vq,
> > -				offsetof(struct vring_used, ring[used_idx]),
> > -				sizeof(vq->used->ring[used_idx]));
> > -		}
> > +error:
> > +	/* rollback on any error if last_used_idx update on-the-fly */
> > +	vq->last_used_idx -= extra_buffers;
> >
> > -		if (i + 1 < count)
> > -			rte_prefetch0(&vq->desc[desc_indexes[i+1]]);
> > -	}
> > +	return 1;
> 
> We normally returns -1 (but not 1) on error.
> 
> >
> > +static inline void __attribute__((always_inline))
> > +notify_guest(struct virtio_net *dev, struct vhost_virtqueue *vq)
> > +{
> >  	rte_smp_wmb();
> > -
> > -	*(volatile uint16_t *)&vq->used->idx += count;
> > -	vq->last_used_idx += count;
> > -	vhost_log_used_vring(dev, vq,
> > -		offsetof(struct vring_used, idx),
> > -		sizeof(vq->used->idx));
> > -
> > -	/* flush used->idx update before we read avail->flags. */
> > +	vq->used->idx = vq->last_used_idx;
> 
> I will not drop the "volatile" cast here, sliently. You know this kind of
> stuff is tricky and would be painful to debug if it cause any issue. Such
> removal deserves a patch, as well as some explanations.
> 
> > +	vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
> > +			sizeof(vq->used->idx));
> >  	rte_mb();
> > -
> > -	/* Kick the guest if necessary. */
> >  	if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> >  			&& (vq->callfd >= 0))
> >  		eventfd_write(vq->callfd, (eventfd_t)1);
> > -	return count;
> >  }
> >
> ...
> > +	/* start enqueuing packets 1 by 1 */
> > +	avail_idx = *((volatile uint16_t *)&vq->avail->idx);
> > +	while (pkt_left && avail_idx != vq->last_used_idx) {
> > +		if (enqueue_packet(dev, vq, avail_idx, pkts[pkt_idx],
> > +					is_mrg_rxbuf))
> >  			break;
> > -		}
> > -
> > -		nr_used = copy_mbuf_to_desc_mergeable(dev, vq, end,
> > -						      pkts[pkt_idx], buf_vec);
> > -		rte_smp_wmb();
> > -
> > -		*(volatile uint16_t *)&vq->used->idx += nr_used;
> > -		vhost_log_used_vring(dev, vq, offsetof(struct vring_used,
> idx),
> > -			sizeof(vq->used->idx));
> > -		vq->last_used_idx += nr_used;
> > -	}
> > -
> > -	if (likely(pkt_idx)) {
> > -		/* flush used->idx update before we read avail->flags. */
> > -		rte_mb();
> >
> > -		/* Kick the guest if necessary. */
> > -		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> > -				&& (vq->callfd >= 0))
> > -			eventfd_write(vq->callfd, (eventfd_t)1);
> > +		pkt_idx++;
> > +		pkt_sent++;
> 
> pkt_idx and pkt_sent is duplicate here.
> 
> 	--yliu
> 
> > +		pkt_left--;
> >  	}
> >
> > -	return pkt_idx;
> > -}
> > -
> > -uint16_t
> > -rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
> > -	struct rte_mbuf **pkts, uint16_t count)
> > -{
> > -	struct virtio_net *dev = get_device(vid);
> > -
> > -	if (!dev)
> > -		return 0;
> > +	/* update used idx and kick the guest if necessary */
> > +	if (pkt_sent)
> > +		notify_guest(dev, vq);
> >
> > -	if (dev->features & (1 << VIRTIO_NET_F_MRG_RXBUF))
> > -		return virtio_dev_merge_rx(dev, queue_id, pkts, count);
> > -	else
> > -		return virtio_dev_rx(dev, queue_id, pkts, count);
> > +	return pkt_sent;
> >  }
> >
> >  static void
> > --
> > 2.7.4