[dpdk-dev] [PATCH v4 1/9] vhost: advertise support in-order feature

[Marvin Liu <yong.liu@intel.com>]

If devices always use descriptors in the same order in which they have
been made available. These devices can offer the VIRTIO_F_IN_ORDER
feature. If negotiated, this knowledge allows devices to notify the use
of a batch of buffers to virtio driver by only writing used ring index.

Vhost user device has supported this feature by default. If vhost
dequeue zero is enabled, should disable VIRTIO_F_IN_ORDER as vhost can’t
assure that descriptors returned from NIC are in order.

Signed-off-by: Marvin Liu <yong.liu@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index 0399c37bc..d63031747 100644
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -853,6 +853,12 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
 	vsocket->supported_features = VIRTIO_NET_SUPPORTED_FEATURES;
 	vsocket->features           = VIRTIO_NET_SUPPORTED_FEATURES;
 
+	/* Dequeue zero copy can't assure descriptors returned in order */
+	if (vsocket->dequeue_zero_copy) {
+		vsocket->supported_features &= ~(1ULL << VIRTIO_F_IN_ORDER);
+		vsocket->features &= ~(1ULL << VIRTIO_F_IN_ORDER);
+	}
+
 	if (!(flags & RTE_VHOST_USER_IOMMU_SUPPORT)) {
 		vsocket->supported_features &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
 		vsocket->features &= ~(1ULL << VIRTIO_F_IOMMU_PLATFORM);
diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 786a74f64..3437b996b 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -191,6 +191,13 @@ struct vhost_msg {
  #define VIRTIO_F_VERSION_1 32
 #endif
 
+/*
+ * Available and used descs are in same order
+ */
+#ifndef VIRTIO_F_IN_ORDER
+#define VIRTIO_F_IN_ORDER      35
+#endif
+
 /* Features supported by this builtin vhost-user net driver. */
 #define VIRTIO_NET_SUPPORTED_FEATURES ((1ULL << VIRTIO_NET_F_MRG_RXBUF) | \
 				(1ULL << VIRTIO_F_ANY_LAYOUT) | \
@@ -214,7 +221,8 @@ struct vhost_msg {
 				(1ULL << VIRTIO_NET_F_GUEST_ECN) | \
 				(1ULL << VIRTIO_RING_F_INDIRECT_DESC) | \
 				(1ULL << VIRTIO_RING_F_EVENT_IDX) | \
-				(1ULL << VIRTIO_NET_F_MTU) | \
+				(1ULL << VIRTIO_NET_F_MTU)  | \
+				(1ULL << VIRTIO_F_IN_ORDER) | \
 				(1ULL << VIRTIO_F_IOMMU_PLATFORM))
 
 
-- 
2.17.0