[dpdk-dev] [PATCH] vhost: remove deferred shadow update
Wang, Yinan
yinan.wang at intel.com
Mon Apr 6 10:56:57 CEST 2020
Tested-by: Wang, Yinan <yinan.wang at intel.com>
> -----Original Message-----
> From: dev <dev-bounces at dpdk.org> On Behalf Of Marvin Liu
> Sent: 2020年4月2日 5:29
> To: maxime.coquelin at redhat.com; Ye, Xiaolong <xiaolong.ye at intel.com>;
> Wang, Zhihong <zhihong.wang at intel.com>; eperezma at redhat.com
> Cc: dev at dpdk.org; Liu, Yong <yong.liu at intel.com>
> Subject: [dpdk-dev] [PATCH] vhost: remove deferred shadow update
>
> Defer shadow ring update will help overall throughput when frontend much
> slower than backend. But that is not all the cases we faced now.
> In case like ovs-dpdk + dpdk virtio user, frontend will much faster than
> backend. Frontend may not be able to collect available descs when shadow
> update is deferred. Thus will harm RFC2544 performance.
>
> Solution is just remove deferred shadow update, which will help RFC2544
> and fix potential issue with virtio net driver.
>
> Signed-off-by: Marvin Liu <yong.liu at intel.com>
>
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index
> 37c47c7dc..2ba0575a7 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -382,25 +382,6 @@ vhost_shadow_enqueue_single_packed(struct
> virtio_net *dev,
> }
> }
>
> -static __rte_always_inline void
> -vhost_flush_dequeue_packed(struct virtio_net *dev,
> - struct vhost_virtqueue *vq)
> -{
> - int shadow_count;
> - if (!vq->shadow_used_idx)
> - return;
> -
> - shadow_count = vq->last_used_idx - vq->shadow_last_used_idx;
> - if (shadow_count <= 0)
> - shadow_count += vq->size;
> -
> - if ((uint32_t)shadow_count >= (vq->size - MAX_PKT_BURST)) {
> - do_data_copy_dequeue(vq);
> - vhost_flush_dequeue_shadow_packed(dev, vq);
> - vhost_vring_call_packed(dev, vq);
> - }
> -}
> -
> /* avoid write operation when necessary, to lessen cache issues */
> #define ASSIGN_UNLESS_EQUAL(var, val) do { \
> if ((var) != (val)) \
> @@ -2133,20 +2114,6 @@ virtio_dev_tx_packed_zmbuf(struct virtio_net
> *dev,
> return pkt_idx;
> }
>
> -static __rte_always_inline bool
> -next_desc_is_avail(const struct vhost_virtqueue *vq) -{
> - bool wrap_counter = vq->avail_wrap_counter;
> - uint16_t next_used_idx = vq->last_used_idx + 1;
> -
> - if (next_used_idx >= vq->size) {
> - next_used_idx -= vq->size;
> - wrap_counter ^= 1;
> - }
> -
> - return desc_is_avail(&vq->desc_packed[next_used_idx],
> wrap_counter);
> -}
> -
> static __rte_noinline uint16_t
> virtio_dev_tx_packed(struct virtio_net *dev,
> struct vhost_virtqueue *vq,
> @@ -2163,7 +2130,6 @@ virtio_dev_tx_packed(struct virtio_net *dev,
> if (remained >= PACKED_BATCH_SIZE) {
> if (!virtio_dev_tx_batch_packed(dev, vq, mbuf_pool,
> &pkts[pkt_idx])) {
> - vhost_flush_dequeue_packed(dev, vq);
> pkt_idx += PACKED_BATCH_SIZE;
> remained -= PACKED_BATCH_SIZE;
> continue;
> @@ -2173,7 +2139,6 @@ virtio_dev_tx_packed(struct virtio_net *dev,
> if (virtio_dev_tx_single_packed(dev, vq, mbuf_pool,
> &pkts[pkt_idx]))
> break;
> - vhost_flush_dequeue_packed(dev, vq);
> pkt_idx++;
> remained--;
>
> @@ -2182,15 +2147,8 @@ virtio_dev_tx_packed(struct virtio_net *dev,
> if (vq->shadow_used_idx) {
> do_data_copy_dequeue(vq);
>
> - if (remained && !next_desc_is_avail(vq)) {
> - /*
> - * The guest may be waiting to TX some buffers to
> - * enqueue more to avoid bufferfloat, so we try to
> - * reduce latency here.
> - */
> - vhost_flush_dequeue_shadow_packed(dev, vq);
> - vhost_vring_call_packed(dev, vq);
> - }
> + vhost_flush_dequeue_shadow_packed(dev, vq);
> + vhost_vring_call_packed(dev, vq);
> }
>
> return pkt_idx;
> --
> 2.17.1
More information about the dev
mailing list