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From f3bf9a1a9b1ad3419b436855306ad8b5d8efab2f Mon Sep 17 00:00:00 2001
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From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Date: Thu, 20 Dec 2018 17:47:55 +0100
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Subject: [PATCH 18/18] vhost: batch used descs chains write-back with packed
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ring
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[ upstream commit b473ec1131ee44ee25e0536a04be65246b93f4f3 ]
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Instead of writing back descriptors chains in order, let's
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write the first chain flags last in order to improve batching.
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Also, move the write barrier in logging cache sync, so that it
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is done only when logging is enabled. It means there is now
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one more barrier for split ring when logging is enabled.
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With Kernel's pktgen benchmark, ~3% performance gain is measured.
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Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
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Acked-by: Michael S. Tsirkin <mst@redhat.com>
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Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>
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(cherry picked from commit b473ec1131ee44ee25e0536a04be65246b93f4f3)
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Signed-off-by: Jens Freimann <jfreimann@redhat.com>
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---
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lib/librte_vhost/vhost.h | 7 ++-----
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lib/librte_vhost/virtio_net.c | 19 ++++++++++++++++---
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2 files changed, 18 insertions(+), 8 deletions(-)
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diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
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index 552b9298d..adc2fb78e 100644
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--- a/lib/librte_vhost/vhost.h
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+++ b/lib/librte_vhost/vhost.h
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@@ -456,12 +456,9 @@ vhost_log_cache_sync(struct virtio_net *dev, struct vhost_virtqueue *vq)
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!dev->log_base))
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return;
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- log_base = (unsigned long *)(uintptr_t)dev->log_base;
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+ rte_smp_wmb();
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- /*
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- * It is expected a write memory barrier has been issued
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- * before this function is called.
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- */
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+ log_base = (unsigned long *)(uintptr_t)dev->log_base;
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for (i = 0; i < vq->log_cache_nb_elem; i++) {
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struct log_cache_entry *elem = vq->log_cache + i;
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diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
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index 15d682c3c..ec70ef947 100644
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--- a/lib/librte_vhost/virtio_net.c
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+++ b/lib/librte_vhost/virtio_net.c
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@@ -136,6 +136,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
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{
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int i;
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uint16_t used_idx = vq->last_used_idx;
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+ uint16_t head_idx = vq->last_used_idx;
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+ uint16_t head_flags = 0;
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/* Split loop in two to save memory barriers */
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for (i = 0; i < vq->shadow_used_idx; i++) {
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@@ -165,12 +167,17 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
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flags &= ~VRING_DESC_F_AVAIL;
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}
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- vq->desc_packed[vq->last_used_idx].flags = flags;
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+ if (i > 0) {
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+ vq->desc_packed[vq->last_used_idx].flags = flags;
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- vhost_log_cache_used_vring(dev, vq,
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+ vhost_log_cache_used_vring(dev, vq,
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vq->last_used_idx *
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sizeof(struct vring_packed_desc),
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sizeof(struct vring_packed_desc));
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+ } else {
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+ head_idx = vq->last_used_idx;
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+ head_flags = flags;
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+ }
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vq->last_used_idx += vq->shadow_used_packed[i].count;
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if (vq->last_used_idx >= vq->size) {
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@@ -179,7 +186,13 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
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}
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}
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- rte_smp_wmb();
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+ vq->desc_packed[head_idx].flags = head_flags;
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+
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+ vhost_log_cache_used_vring(dev, vq,
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+ head_idx *
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+ sizeof(struct vring_packed_desc),
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+ sizeof(struct vring_packed_desc));
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+
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vq->shadow_used_idx = 0;
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vhost_log_cache_sync(dev, vq);
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}
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--
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2.21.0
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