[dpdk-dev] [RFC v2 1/2] vhost: populate guest memory for DMA-accelerated vhost-user

[Jiayu Hu <jiayu.hu@intel.com>]

DMA engines, like I/OAT, are efficient in moving large data
within memory. Offloading large copies in vhost side to DMA
engines can save precious CPU cycles and improve vhost
performance.

However, using the DMA engine requires to populate guest's
memory. This patch is to enable DMA-accelerated vhost-user
to populate guest's memory.

Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
---
 lib/librte_vhost/rte_vhost.h  |  1 +
 lib/librte_vhost/socket.c     | 11 +++++++++++
 lib/librte_vhost/vhost.h      |  2 ++
 lib/librte_vhost/vhost_user.c |  3 ++-
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
index 7b5dc87..7716939 100644
--- a/lib/librte_vhost/rte_vhost.h
+++ b/lib/librte_vhost/rte_vhost.h
@@ -34,6 +34,7 @@ extern "C" {
 #define RTE_VHOST_USER_EXTBUF_SUPPORT	(1ULL << 5)
 /* support only linear buffers (no chained mbufs) */
 #define RTE_VHOST_USER_LINEARBUF_SUPPORT	(1ULL << 6)
+#define RTE_VHOST_USER_DMA_COPY		(1ULL << 7)
 
 /** Protocol features. */
 #ifndef VHOST_USER_PROTOCOL_F_MQ
diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
index a34bc7f..9db6f6b 100644
--- a/lib/librte_vhost/socket.c
+++ b/lib/librte_vhost/socket.c
@@ -62,6 +62,8 @@ struct vhost_user_socket {
 	 */
 	int vdpa_dev_id;
 
+	bool dma_enabled;
+
 	struct vhost_device_ops const *notify_ops;
 };
 
@@ -240,6 +242,13 @@ vhost_user_add_connection(int fd, struct vhost_user_socket *vsocket)
 	if (vsocket->linearbuf)
 		vhost_enable_linearbuf(vid);
 
+	if (vsocket->dma_enabled) {
+		struct virtio_net *dev;
+
+		dev = get_device(vid);
+		dev->dma_enabled = true;
+	}
+
 	RTE_LOG(INFO, VHOST_CONFIG, "new device, handle is %d\n", vid);
 
 	if (vsocket->notify_ops->new_connection) {
@@ -889,6 +898,8 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
 		goto out_mutex;
 	}
 
+	vsocket->dma_enabled = flags & RTE_VHOST_USER_DMA_COPY;
+
 	/*
 	 * Set the supported features correctly for the builtin vhost-user
 	 * net driver.
diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index 9f11b28..b61a790 100644
--- a/lib/librte_vhost/vhost.h
+++ b/lib/librte_vhost/vhost.h
@@ -383,6 +383,8 @@ struct virtio_net {
 	 */
 	int			vdpa_dev_id;
 
+	bool			dma_enabled;
+
 	/* context data for the external message handlers */
 	void			*extern_data;
 	/* pre and post vhost user message handlers for the device */
diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 2a9fa7c..12722b9 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -1067,7 +1067,8 @@ vhost_user_set_mem_table(struct virtio_net **pdev, struct VhostUserMsg *msg,
 		}
 		mmap_size = RTE_ALIGN_CEIL(mmap_size, alignment);
 
-		populate = (dev->dequeue_zero_copy) ? MAP_POPULATE : 0;
+		populate = (dev->dequeue_zero_copy || dev->dma_enabled) ?
+			MAP_POPULATE : 0;
 		mmap_addr = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE,
 				 MAP_SHARED | populate, fd, 0);
 
-- 
2.7.4