From e7ef688562b69076e79ca132de05cb0be732792d Mon Sep 17 00:00:00 2001 From: Zhihong Wang Date: Fri, 14 Oct 2016 17:34:33 +0800 Subject: [PATCH] vhost: optimize cache access This patch reorders the code to delay virtio header write to improve cache access efficiency for cases where the mrg_rxbuf feature is turned on. CPU pipeline stall cycles can be significantly reduced. Virtio header write and mbuf data copy are all remote store operations which takes a long time to finish. It's a good idea to put them together to remove bubbles in between, to let as many remote store instructions as possible go into store buffer at the same time to hide latency, and to let the H/W prefetcher goes to work as early as possible. On a Haswell machine, about 100 cycles can be saved per packet by this patch alone. Taking 64B packets traffic for example, this means about 60% efficiency improvement for the enqueue operation. Signed-off-by: Zhihong Wang Signed-off-by: Yuanhan Liu Reviewed-by: Jianbo Liu Tested-by: Maxime Coquelin --- lib/librte_vhost/virtio_net.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index 15ef0b0bbf..27ebf3de49 100644 --- a/lib/librte_vhost/virtio_net.c +++ b/lib/librte_vhost/virtio_net.c @@ -390,6 +390,8 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq, uint32_t desc_offset, desc_avail; uint32_t cpy_len; uint16_t desc_idx, used_idx; + uint64_t hdr_addr, hdr_phys_addr; + struct rte_mbuf *hdr_mbuf; if (unlikely(m == NULL)) return 0; @@ -401,17 +403,15 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq, if (buf_vec[vec_idx].buf_len < dev->vhost_hlen || !desc_addr) return 0; - rte_prefetch0((void *)(uintptr_t)desc_addr); + hdr_mbuf = m; + hdr_addr = desc_addr; + hdr_phys_addr = buf_vec[vec_idx].buf_addr; + rte_prefetch0((void *)(uintptr_t)hdr_addr); virtio_hdr.num_buffers = end_idx - start_idx; LOG_DEBUG(VHOST_DATA, "(%d) RX: num merge buffers %d\n", dev->vid, virtio_hdr.num_buffers); - virtio_enqueue_offload(m, &virtio_hdr.hdr); - copy_virtio_net_hdr(dev, desc_addr, virtio_hdr); - vhost_log_write(dev, buf_vec[vec_idx].buf_addr, dev->vhost_hlen); - PRINT_PACKET(dev, (uintptr_t)desc_addr, dev->vhost_hlen, 0); - desc_avail = buf_vec[vec_idx].buf_len - dev->vhost_hlen; desc_offset = dev->vhost_hlen; desc_chain_head = buf_vec[vec_idx].desc_idx; @@ -456,6 +456,16 @@ copy_mbuf_to_desc_mergeable(struct virtio_net *dev, struct vhost_virtqueue *vq, mbuf_avail = rte_pktmbuf_data_len(m); } + if (hdr_addr) { + virtio_enqueue_offload(hdr_mbuf, &virtio_hdr.hdr); + copy_virtio_net_hdr(dev, hdr_addr, virtio_hdr); + vhost_log_write(dev, hdr_phys_addr, dev->vhost_hlen); + PRINT_PACKET(dev, (uintptr_t)hdr_addr, + dev->vhost_hlen, 0); + + hdr_addr = 0; + } + 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), -- 2.20.1