[dpdk-dev] [PATCH v5 5/6] vhost: batch update used ring

Wang, Zhihong zhihong.wang at intel.com
Wed Sep 14 10:43:30 CEST 2016



> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com]
> Sent: Monday, September 12, 2016 11:46 PM
> To: Wang, Zhihong <zhihong.wang at intel.com>; dev at dpdk.org
> Cc: yuanhan.liu at linux.intel.com; thomas.monjalon at 6wind.com
> Subject: Re: [PATCH v5 5/6] vhost: batch update used ring
> 
> 
> 
> On 09/09/2016 05:39 AM, Zhihong Wang wrote:
> > This patch enables batch update of the used ring for better efficiency.
> >
> > Signed-off-by: Zhihong Wang <zhihong.wang at intel.com>
> > ---
> > Changes in v4:
> >
> >  1. Free shadow used ring in the right place.
> >
> >  2. Add failure check for shadow used ring malloc.
> >
> >  lib/librte_vhost/vhost.c      | 20 ++++++++++++--
> >  lib/librte_vhost/vhost.h      |  4 +++
> >  lib/librte_vhost/vhost_user.c | 31 +++++++++++++++++----
> >  lib/librte_vhost/virtio_net.c | 64
> +++++++++++++++++++++++++++++++++++--------
> >  4 files changed, 101 insertions(+), 18 deletions(-)
> >
> > diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> > index 46095c3..cb31cdd 100644
> > --- a/lib/librte_vhost/vhost.c
> > +++ b/lib/librte_vhost/vhost.c
> > @@ -119,10 +119,26 @@ cleanup_device(struct virtio_net *dev, int
> destroy)
> >  static void
> >  free_device(struct virtio_net *dev)
> >  {
> > +	struct vhost_virtqueue *vq_0;
> > +	struct vhost_virtqueue *vq_1;
> >  	uint32_t i;
> >
> > -	for (i = 0; i < dev->virt_qp_nb; i++)
> > -		rte_free(dev->virtqueue[i * VIRTIO_QNUM]);
> > +	for (i = 0; i < dev->virt_qp_nb; i++) {
> > +		vq_0 = dev->virtqueue[i * VIRTIO_QNUM];
> > +		if (vq_0->shadow_used_ring) {
> > +			rte_free(vq_0->shadow_used_ring);
> > +			vq_0->shadow_used_ring = NULL;
> > +		}
> > +
> > +		vq_1 = dev->virtqueue[i * VIRTIO_QNUM + 1];
> > +		if (vq_1->shadow_used_ring) {
> > +			rte_free(vq_1->shadow_used_ring);
> > +			vq_1->shadow_used_ring = NULL;
> > +		}
> > +
> > +		/* malloc together, free together */
> > +		rte_free(vq_0);
> > +	}
> >
> >  	rte_free(dev);
> >  }
> > diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> > index 9707dfc..381dc27 100644
> > --- a/lib/librte_vhost/vhost.h
> > +++ b/lib/librte_vhost/vhost.h
> > @@ -85,6 +85,10 @@ struct vhost_virtqueue {
> >
> >  	/* Physical address of used ring, for logging */
> >  	uint64_t		log_guest_addr;
> > +
> > +	/* Shadow used ring for performance */
> > +	struct vring_used_elem	*shadow_used_ring;
> > +	uint32_t		shadow_used_idx;
> >  } __rte_cache_aligned;
> >
> >  /* Old kernels have no such macro defined */
> > diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> > index eee99e9..d7cf1ed 100644
> > --- a/lib/librte_vhost/vhost_user.c
> > +++ b/lib/librte_vhost/vhost_user.c
> > @@ -193,7 +193,21 @@ static int
> >  vhost_user_set_vring_num(struct virtio_net *dev,
> >  			 struct vhost_vring_state *state)
> >  {
> > -	dev->virtqueue[state->index]->size = state->num;
> > +	struct vhost_virtqueue *vq;
> > +
> > +	vq = dev->virtqueue[state->index];
> > +	vq->size = state->num;
> > +	if (!vq->shadow_used_ring) {
> > +		vq->shadow_used_ring = rte_malloc(NULL,
> > +				vq->size * sizeof(struct vring_used_elem),
> > +				RTE_CACHE_LINE_SIZE);
> > +		if (!vq->shadow_used_ring) {
> > +			RTE_LOG(ERR, VHOST_CONFIG,
> > +				"Failed to allocate memory"
> > +				" for shadow used ring.\n");
> > +			return -1;
> > +		}
> > +	}
> >
> >  	return 0;
> >  }
> > @@ -611,14 +625,21 @@ static int
> >  vhost_user_get_vring_base(struct virtio_net *dev,
> >  			  struct vhost_vring_state *state)
> >  {
> > +	struct vhost_virtqueue *vq;
> > +
> >  	/* We have to stop the queue (virtio) if it is running. */
> >  	if (dev->flags & VIRTIO_DEV_RUNNING) {
> >  		dev->flags &= ~VIRTIO_DEV_RUNNING;
> >  		notify_ops->destroy_device(dev->vid);
> >  	}
> >
> > +	vq = dev->virtqueue[state->index];
> >  	/* Here we are safe to get the last used index */
> > -	state->num = dev->virtqueue[state->index]->last_used_idx;
> > +	state->num = vq->last_used_idx;
> > +	if (vq->shadow_used_ring) {
> > +		rte_free(vq->shadow_used_ring);
> > +		vq->shadow_used_ring = NULL;
> > +	}
> >
> >  	RTE_LOG(INFO, VHOST_CONFIG,
> >  		"vring base idx:%d file:%d\n", state->index, state->num);
> > @@ -627,10 +648,10 @@ vhost_user_get_vring_base(struct virtio_net
> *dev,
> >  	 * sent and only sent in vhost_vring_stop.
> >  	 * TODO: cleanup the vring, it isn't usable since here.
> >  	 */
> > -	if (dev->virtqueue[state->index]->kickfd >= 0)
> > -		close(dev->virtqueue[state->index]->kickfd);
> > +	if (vq->kickfd >= 0)
> > +		close(vq->kickfd);
> >
> > -	dev->virtqueue[state->index]->kickfd =
> VIRTIO_UNINITIALIZED_EVENTFD;
> > +	vq->kickfd = VIRTIO_UNINITIALIZED_EVENTFD;
> >
> >  	return 0;
> >  }
> > diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> > index b38f18f..e9f6353 100644
> > --- a/lib/librte_vhost/virtio_net.c
> > +++ b/lib/librte_vhost/virtio_net.c
> > @@ -134,17 +134,52 @@ virtio_enqueue_offload(struct rte_mbuf
> *m_buf, struct virtio_net_hdr *net_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)
> > +update_used_ring(struct vhost_virtqueue *vq, uint32_t
> desc_chain_head,
> > +		uint32_t desc_chain_len)
> >  {
> > -	uint32_t used_idx = vq->last_used_idx & (vq->size - 1);
> > -
> > -	vq->used->ring[used_idx].id = desc_chain_head;
> > -	vq->used->ring[used_idx].len = desc_chain_len;
> > +	vq->shadow_used_ring[vq->shadow_used_idx].id  =
> desc_chain_head;
> > +	vq->shadow_used_ring[vq->shadow_used_idx].len =
> desc_chain_len;
> > +	vq->shadow_used_idx++;
> >  	vq->last_used_idx++;
> > -	vhost_log_used_vring(dev, vq, offsetof(struct vring_used,
> > -				ring[used_idx]),
> > -			sizeof(vq->used->ring[used_idx]));
> > +}
> > +
> > +static inline void __attribute__((always_inline))
> > +flush_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
> > +		uint32_t used_idx_start)
> > +{
> > +	if (used_idx_start + vq->shadow_used_idx < vq->size) {
> > +		rte_memcpy(&vq->used->ring[used_idx_start],
> > +				&vq->shadow_used_ring[0],
> > +				vq->shadow_used_idx *
> > +				sizeof(struct vring_used_elem));
> > +		vhost_log_used_vring(dev, vq,
> > +				offsetof(struct vring_used,
> > +					ring[used_idx_start]),
> > +				vq->shadow_used_idx *
> > +				sizeof(struct vring_used_elem));
> > +	} else {
> > +		uint32_t part_1 = vq->size - used_idx_start;
> > +		uint32_t part_2 = vq->shadow_used_idx - part_1;
> > +
> > +		rte_memcpy(&vq->used->ring[used_idx_start],
> > +				&vq->shadow_used_ring[0],
> > +				part_1 *
> > +				sizeof(struct vring_used_elem));
> > +		vhost_log_used_vring(dev, vq,
> > +				offsetof(struct vring_used,
> > +					ring[used_idx_start]),
> > +				part_1 *
> > +				sizeof(struct vring_used_elem));
> > +		rte_memcpy(&vq->used->ring[0],
> > +				&vq->shadow_used_ring[part_1],
> > +				part_2 *
> > +				sizeof(struct vring_used_elem));
> > +		vhost_log_used_vring(dev, vq,
> > +				offsetof(struct vring_used,
> > +					ring[0]),
> > +				part_2 *
> > +				sizeof(struct vring_used_elem));
> > +	}
> >  }
> Is expanding the code done for performance purpose?

Hi Maxime,

Yes theoretically this has the least branch number.
And I think the logic is simpler this way.

Thanks
Zhihong

> Or maybe we could have a loop to do that?
> Something like this (not compiled, not tested):
> 
> static inline void __attribute__((always_inline))
> flush_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
> {
> 	uint32_t to = used_idx_start;
> 	uint32_t from = 0;
> 	uint32_t count;
> 
> 	if (used_idx_start + vq->shadow_used_idx < vq->size)
> 		count = vq->shadow_used_idx;
> 	else
> 		count = vq->size - used_idx_start;
> 
> 	do {
> 		rte_memcpy(&vq->used->ring[to],
> 				&vq->shadow_used_ring[from],
> 				count * sizeof(struct vring_used_elem));
> 		vhost_log_used_vring(dev, vq,
> 				offsetof(struct vring_used, ring[to]),
> 				count * sizeof(struct vring_used_elem));
> 
> 		to = (to + count) & (vq->size - 1);
> 		from += count;
> 		count = vq->shadow_used_idx - count;
> 	} while (count);
> }
> 
> Regards,
> Maxime


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