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From: Maxime Coquelin <maxime.coquelin@redhat.com>
To: dev@dpdk.org, i.maximets@samsung.com, tiwei.bie@intel.com,
	zhihong.wang@intel.com, jfreiman@redhat.com, mst@redhat.com
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Subject: [dpdk-dev] [PATCH v2] vhost: batch used descs chains write-back with packed ring
Date: Wed, 19 Dec 2018 10:29:52 +0100	[thread overview]
Message-ID: <20181219092952.25728-1-maxime.coquelin@redhat.com> (raw)

Instead of writing back descriptors chains in order, let's
write the first chain flags last in order to improve batching.

With Kernel's pktgen benchmark, ~3% performance gain is measured.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---

V2:
Revert back to initial implementation to have a write
barrier before every descs flags store, but still
store first desc flags last. (Missing barrier reported
by Ilya)


 lib/librte_vhost/virtio_net.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 8c657a101..de436af79 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,
+				vq->last_used_idx *
+				sizeof(struct vring_packed_desc),
+				sizeof(struct vring_packed_desc));
+
 	vq->shadow_used_idx = 0;
 	vhost_log_cache_sync(dev, vq);
 }
-- 
2.17.2

             reply	other threads:[~2018-12-19  9:30 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-19  9:29 Maxime Coquelin [this message]
2018-12-19 16:43 ` Michael S. Tsirkin
2018-12-20  4:44 ` Tiwei Bie
2018-12-20  8:49   ` Maxime Coquelin
2018-12-20  9:27     ` Maxime Coquelin
2018-12-20 14:03   ` Michael S. Tsirkin

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