From 8b13d12a16e7da07326f75bb8b5b82a39bdcbe9e Mon Sep 17 00:00:00 2001 From: Marvin Liu Date: Fri, 17 Apr 2020 10:39:05 +0800 Subject: [PATCH] vhost: fix shadow update Defer shadow ring update introduces functional issue which has been described in Eugenio's fix patch. The current implementation of vhost_net in packed vring tries to fill the shadow vector before send any actual changes to the guest. While this can be beneficial for the throughput, it conflicts with some bufferfloats methods like the linux kernel napi, that stops transmitting packets if there are too much bytes/buffers in the driver. It also introduces performance issue when frontend run much faster than backend. Frontend may not be able to collect available descs when shadow update is deferred. That will harm RFC2544 throughput. Appropriate choice is to remove deferred shadowed update method. Now shadowed used descs are flushed at the end of dequeue function. Fixes: 31d6c6a5b820 ("vhost: optimize packed ring dequeue") Cc: stable@dpdk.org Signed-off-by: Marvin Liu Tested-by: Yinan Wang Reviewed-by: Maxime Coquelin --- lib/librte_vhost/virtio_net.c | 46 ++--------------------------------- 1 file changed, 2 insertions(+), 44 deletions(-) diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index 2104159047..4a75319432 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; -- 2.20.1