From b473ec1131ee44ee25e0536a04be65246b93f4f3 Mon Sep 17 00:00:00 2001 From: Maxime Coquelin Date: Thu, 20 Dec 2018 17:47:55 +0100 Subject: [PATCH] vhost: batch used descs chains write-back with packed ring Instead of writing back descriptors chains in order, let's write the first chain flags last in order to improve batching. Also, move the write barrier in logging cache sync, so that it is done only when logging is enabled. It means there is now one more barrier for split ring when logging is enabled. With Kernel's pktgen benchmark, ~3% performance gain is measured. Signed-off-by: Maxime Coquelin Acked-by: Michael S. Tsirkin Reviewed-by: Tiwei Bie --- lib/librte_vhost/vhost.h | 7 ++----- lib/librte_vhost/virtio_net.c | 19 ++++++++++++++++--- 2 files changed, 18 insertions(+), 8 deletions(-) diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h index 3b3265c4b6..f267f898ca 100644 --- a/lib/librte_vhost/vhost.h +++ b/lib/librte_vhost/vhost.h @@ -457,12 +457,9 @@ vhost_log_cache_sync(struct virtio_net *dev, struct vhost_virtqueue *vq) !dev->log_base)) return; - log_base = (unsigned long *)(uintptr_t)dev->log_base; + rte_smp_wmb(); - /* - * It is expected a write memory barrier has been issued - * before this function is called. - */ + log_base = (unsigned long *)(uintptr_t)dev->log_base; for (i = 0; i < vq->log_cache_nb_elem; i++) { struct log_cache_entry *elem = vq->log_cache + i; diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index 4d201a3fd2..474acf64dd 100644 --- a/lib/librte_vhost/virtio_net.c +++ b/lib/librte_vhost/virtio_net.c @@ -97,6 +97,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, { int i; uint16_t used_idx = vq->last_used_idx; + uint16_t head_idx = vq->last_used_idx; + uint16_t head_flags = 0; /* Split loop in two to save memory barriers */ for (i = 0; i < vq->shadow_used_idx; i++) { @@ -126,12 +128,17 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, flags &= ~VRING_DESC_F_AVAIL; } - vq->desc_packed[vq->last_used_idx].flags = flags; + if (i > 0) { + vq->desc_packed[vq->last_used_idx].flags = flags; - vhost_log_cache_used_vring(dev, vq, + vhost_log_cache_used_vring(dev, vq, vq->last_used_idx * sizeof(struct vring_packed_desc), sizeof(struct vring_packed_desc)); + } else { + head_idx = vq->last_used_idx; + head_flags = flags; + } vq->last_used_idx += vq->shadow_used_packed[i].count; if (vq->last_used_idx >= vq->size) { @@ -140,7 +147,13 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, } } - rte_smp_wmb(); + vq->desc_packed[head_idx].flags = head_flags; + + vhost_log_cache_used_vring(dev, vq, + head_idx * + sizeof(struct vring_packed_desc), + sizeof(struct vring_packed_desc)); + vq->shadow_used_idx = 0; vhost_log_cache_sync(dev, vq); } -- 2.20.1