> -----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
