Re: [dpdk-dev] [PATCH v2] vhost: add support for large buffers.

[Tiwei Bie <tiwei.bie@intel.com>]

[PATCH v2] vhost: add support for large buffers.

There is a warning reported by devtools/check-git-log.sh
The '.' at the end of the title should be dropped.

On Fri, Oct 04, 2019 at 05:10:08PM -0300, Flavio Leitner wrote:
> The rte_vhost_dequeue_burst supports two ways of dequeuing data.
> If the data fits into a buffer, then all data is copied and a
> single linear buffer is returned. Otherwise it allocates
> additional mbufs and chains them together to return a multiple
> segments mbuf.
> 
> While that covers most use cases, it forces applications that
> need to work with larger data sizes to support multiple segments
> mbufs. The non-linear characteristic brings complexity and
> performance implications to the application.
> 
> To resolve the issue, let the host provide during registration
> if attaching an external buffer to pktmbuf is supported and if
> only linear buffer are supported.
> 
> Signed-off-by: Flavio Leitner <fbl@sysclose.org>
> ---
>  doc/guides/prog_guide/vhost_lib.rst |  35 ++++++++++
>  lib/librte_vhost/rte_vhost.h        |   4 ++
>  lib/librte_vhost/socket.c           |  10 +++
>  lib/librte_vhost/vhost.c            |  22 ++++++
>  lib/librte_vhost/vhost.h            |   4 ++
>  lib/librte_vhost/virtio_net.c       | 103 ++++++++++++++++++++++++++--
>  6 files changed, 172 insertions(+), 6 deletions(-)
> 
> - Changelog:
>   V2:
>     - Used rte_malloc() instead of another mempool as suggested by Shahaf.
>     - Added the documentation section.
>     - Using driver registration to negotiate the features.
>     - OvS PoC code:
>       https://github.com/fleitner/ovs/commit/8fc197c40b1d4fda331686a7b919e9e2b670dda7
> 
> diff --git a/doc/guides/prog_guide/vhost_lib.rst b/doc/guides/prog_guide/vhost_lib.rst
> index fc3ee4353..07e40e3c5 100644
> --- a/doc/guides/prog_guide/vhost_lib.rst
> +++ b/doc/guides/prog_guide/vhost_lib.rst
> @@ -117,6 +117,41 @@ The following is an overview of some key Vhost API functions:
>      Enabling this flag should only be done when the calling application does
>      not pre-fault the guest shared memory, otherwise migration would fail.
>  
> +  - ``RTE_VHOST_USER_LINEARBUF_SUPPORT``
> +
> +    Enabling this flag forces vhost dequeue function to only provide linear
> +    pktmbuf (no multi-segmented pktmbuf).
> +
> +    The vhost library by default provides a single pktmbuf for given a
> +    packet, but if for some reason the data doesn't fit into a single
> +    pktmbuf (e.g., TSO is enabled), the library will allocate additional
> +    pktmbufs from the same mempool and chain them together to create a
> +    multi-segmented pktmbuf.
> +
> +    However, the vhost application needs to support multi-segmented format.
> +    If the vhost application does not support that format and requires large
> +    buffers to be dequeue, this flag should be enabled to force only linear
> +    buffers (see RTE_VHOST_USER_EXTBUF_SUPPORT) or drop the packet.
> +
> +    It is disabled by default.
> +
> +  - ``RTE_VHOST_USER_EXTBUF_SUPPORT``
> +
> +    Enabling this flag allows vhost dequeue function to allocate and attach
> +    an external buffer to a pktmbuf if the pkmbuf doesn't provide enough
> +    space to store all data.
> +
> +    This is useful when the vhost application wants to support large packets
> +    but doesn't want to increase the default mempool object size nor to
> +    support multi-segmented mbufs (non-linear). In this case, a fresh buffer
> +    is allocated using rte_malloc() which gets attached to a pktmbuf using
> +    rte_pktmbuf_attach_extbuf().
> +
> +    See RTE_VHOST_USER_LINEARBUF_SUPPORT as well to disable multi-segmented
> +    mbufs for application that doesn't support chained mbufs.
> +
> +    It is disabled by default.
> +
>  * ``rte_vhost_driver_set_features(path, features)``
>  
>    This function sets the feature bits the vhost-user driver supports. The
> diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
> index 19474bca0..b821b5df4 100644
> --- a/lib/librte_vhost/rte_vhost.h
> +++ b/lib/librte_vhost/rte_vhost.h
> @@ -30,6 +30,10 @@ extern "C" {
>  #define RTE_VHOST_USER_DEQUEUE_ZERO_COPY	(1ULL << 2)
>  #define RTE_VHOST_USER_IOMMU_SUPPORT	(1ULL << 3)
>  #define RTE_VHOST_USER_POSTCOPY_SUPPORT		(1ULL << 4)
> +/* support mbuf with external buffer attached */
> +#define RTE_VHOST_USER_EXTBUF_SUPPORT	(1ULL << 5)
> +/* support only linear buffers (no chained mbufs) */
> +#define RTE_VHOST_USER_LINEARBUF_SUPPORT	(1ULL << 6)
>  
>  /** Protocol features. */
>  #ifndef VHOST_USER_PROTOCOL_F_MQ
> diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
> index 274988c4d..0ba610fda 100644
> --- a/lib/librte_vhost/socket.c
> +++ b/lib/librte_vhost/socket.c
> @@ -40,6 +40,8 @@ struct vhost_user_socket {
>  	bool dequeue_zero_copy;
>  	bool iommu_support;
>  	bool use_builtin_virtio_net;
> +	bool extbuf;
> +	bool linearbuf;
>  
>  	/*
>  	 * The "supported_features" indicates the feature bits the
> @@ -232,6 +234,12 @@ vhost_user_add_connection(int fd, struct vhost_user_socket *vsocket)
>  	if (vsocket->dequeue_zero_copy)
>  		vhost_enable_dequeue_zero_copy(vid);
>  
> +	if (vsocket->extbuf)
> +		vhost_enable_extbuf(vid);
> +
> +	if (vsocket->linearbuf)
> +		vhost_enable_linearbuf(vid);
> +
>  	RTE_LOG(INFO, VHOST_CONFIG, "new device, handle is %d\n", vid);
>  
>  	if (vsocket->notify_ops->new_connection) {
> @@ -870,6 +878,8 @@ rte_vhost_driver_register(const char *path, uint64_t flags)
>  		goto out_free;
>  	}
>  	vsocket->dequeue_zero_copy = flags & RTE_VHOST_USER_DEQUEUE_ZERO_COPY;
> +	vsocket->extbuf = flags & RTE_VHOST_USER_EXTBUF_SUPPORT;
> +	vsocket->linearbuf = flags & RTE_VHOST_USER_LINEARBUF_SUPPORT;

It could be problematic to use dequeue_zero_copy with
above two features at the same time.
We may want to reject such combination.

>  
>  	/*
>  	 * Set the supported features correctly for the builtin vhost-user
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index cea44df8c..77457f538 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -605,6 +605,28 @@ vhost_set_builtin_virtio_net(int vid, bool enable)
>  		dev->flags &= ~VIRTIO_DEV_BUILTIN_VIRTIO_NET;
>  }
>  
> +void
> +vhost_enable_extbuf(int vid)
> +{
> +	struct virtio_net *dev = get_device(vid);
> +
> +	if (dev == NULL)
> +		return;
> +
> +	dev->extbuf = 1;
> +}
> +
> +void
> +vhost_enable_linearbuf(int vid)
> +{
> +	struct virtio_net *dev = get_device(vid);
> +
> +	if (dev == NULL)
> +		return;
> +
> +	dev->linearbuf = 1;
> +}
> +
>  int
>  rte_vhost_get_mtu(int vid, uint16_t *mtu)
>  {
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 5131a97a3..0346bd118 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -302,6 +302,8 @@ struct virtio_net {
>  	rte_atomic16_t		broadcast_rarp;
>  	uint32_t		nr_vring;
>  	int			dequeue_zero_copy;
> +	int			extbuf;
> +	int			linearbuf;
>  	struct vhost_virtqueue	*virtqueue[VHOST_MAX_QUEUE_PAIRS * 2];
>  #define IF_NAME_SZ (PATH_MAX > IFNAMSIZ ? PATH_MAX : IFNAMSIZ)
>  	char			ifname[IF_NAME_SZ];
> @@ -476,6 +478,8 @@ void vhost_attach_vdpa_device(int vid, int did);
>  void vhost_set_ifname(int, const char *if_name, unsigned int if_len);
>  void vhost_enable_dequeue_zero_copy(int vid);
>  void vhost_set_builtin_virtio_net(int vid, bool enable);
> +void vhost_enable_extbuf(int vid);
> +void vhost_enable_linearbuf(int vid);
>  
>  struct vhost_device_ops const *vhost_driver_callback_get(const char *path);
>  
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index 5b85b832d..fca75161d 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -2,6 +2,7 @@
>   * Copyright(c) 2010-2016 Intel Corporation
>   */
>  
> +#include <assert.h>
>  #include <stdint.h>
>  #include <stdbool.h>
>  #include <linux/virtio_net.h>
> @@ -1289,6 +1290,96 @@ get_zmbuf(struct vhost_virtqueue *vq)
>  	return NULL;
>  }
>  
> +static void
> +virtio_dev_extbuf_free(void *addr __rte_unused, void *opaque)
> +{
> +	rte_free(opaque);
> +}
> +
> +static int
> +virtio_dev_extbuf_alloc(struct rte_mbuf *pkt, uint16_t size)
> +{
> +	struct rte_mbuf_ext_shared_info *shinfo;
> +	uint16_t buf_len;

It also includes RTE_PKTMBUF_HEADROOM and sizeof(*shinfo).
Is uint16_t big enough?

> +	rte_iova_t iova;
> +	void *buf;
> +
> +	shinfo = NULL;
> +	buf_len = size + RTE_PKTMBUF_HEADROOM;
> +
> +	/* Try to use pkt buffer to store shinfo to reduce the amount of memory
> +	 * required, otherwise store shinfo in the new buffer.
> +	 */
> +	if (rte_pktmbuf_tailroom(pkt) > sizeof(*shinfo))
> +		shinfo = rte_pktmbuf_mtod(pkt,
> +					  struct rte_mbuf_ext_shared_info *);
> +	else {
> +		if (unlikely(buf_len + sizeof(shinfo) > UINT16_MAX)) {

Should be sizeof(*shinfo)

> +			RTE_LOG(ERR, VHOST_DATA,
> +				"buffer size exceeded maximum.\n");
> +			return -ENOSPC;
> +		}
> +
> +		buf_len += sizeof(shinfo);

Ditto.

> +	}
> +
> +	buf = rte_malloc(NULL, buf_len, RTE_CACHE_LINE_SIZE);
> +	if (unlikely(buf == NULL)) {
> +		RTE_LOG(ERR, VHOST_DATA,
> +				"Failed to allocate memory for mbuf.\n");

Looks better to just have 3 tabs before the string.

> +		return -ENOMEM;
> +	}
> +
> +	/* initialize shinfo */
> +	if (shinfo) {
> +		shinfo->free_cb = virtio_dev_extbuf_free;
> +		shinfo->fcb_opaque = buf;
> +		rte_mbuf_ext_refcnt_set(shinfo, 1);
> +	} else {
> +		shinfo = rte_pktmbuf_ext_shinfo_init_helper(buf, &buf_len,
> +					      virtio_dev_extbuf_free, buf);
> +		assert(shinfo);

As a library, we shouldn't abort the process.
We can just return the error.

> +	}
> +
> +	iova = rte_mempool_virt2iova(buf);

Should be rte_malloc_virt2iova().

> +	rte_pktmbuf_attach_extbuf(pkt, buf, iova, buf_len, shinfo);
> +	rte_pktmbuf_reset_headroom(pkt);
> +	assert(pkt->ol_flags == EXT_ATTACHED_MBUF);

Ditto.

> +
> +	return 0;
> +}
> +
> +/*
> + * Allocate a host supported pktmbuf.
> + */
> +static __rte_always_inline struct rte_mbuf *
> +virtio_dev_pktmbuf_alloc(struct virtio_net *dev, struct rte_mempool *mp,
> +			 uint16_t data_len)
> +{
> +	struct rte_mbuf *pkt = rte_pktmbuf_alloc(mp);
> +
> +	if (unlikely(pkt == NULL))
> +		return NULL;
> +
> +	if (rte_pktmbuf_tailroom(pkt) >= data_len)
> +		return pkt;
> +
> +	/* attach an external buffer if supported */
> +	if (dev->extbuf && !virtio_dev_extbuf_alloc(pkt, data_len))
> +		return pkt;
> +
> +	/* check if chained buffers are allowed */
> +	if (!dev->linearbuf)
> +		return pkt;
> +
> +	/* Data doesn't fit into the buffer and the host supports
> +	 * only linear buffers
> +	 */
> +	rte_pktmbuf_free(pkt);
> +
> +	return NULL;
> +}
> +
>  static __rte_noinline uint16_t
>  virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  	struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t count)
> @@ -1343,21 +1434,21 @@ virtio_dev_tx_split(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  	for (i = 0; i < count; i++) {
>  		struct buf_vector buf_vec[BUF_VECTOR_MAX];
>  		uint16_t head_idx;
> -		uint32_t dummy_len;
> +		uint32_t buf_len;
>  		uint16_t nr_vec = 0;
>  		int err;
>  
>  		if (unlikely(fill_vec_buf_split(dev, vq,
>  						vq->last_avail_idx + i,
>  						&nr_vec, buf_vec,
> -						&head_idx, &dummy_len,
> +						&head_idx, &buf_len,
>  						VHOST_ACCESS_RO) < 0))
>  			break;
>  
>  		if (likely(dev->dequeue_zero_copy == 0))
>  			update_shadow_used_ring_split(vq, head_idx, 0);
>  
> -		pkts[i] = rte_pktmbuf_alloc(mbuf_pool);
> +		pkts[i] = virtio_dev_pktmbuf_alloc(dev, mbuf_pool, buf_len);
>  		if (unlikely(pkts[i] == NULL)) {
>  			RTE_LOG(ERR, VHOST_DATA,
>  				"Failed to allocate memory for mbuf.\n");
> @@ -1451,14 +1542,14 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  	for (i = 0; i < count; i++) {
>  		struct buf_vector buf_vec[BUF_VECTOR_MAX];
>  		uint16_t buf_id;
> -		uint32_t dummy_len;
> +		uint32_t buf_len;
>  		uint16_t desc_count, nr_vec = 0;
>  		int err;
>  
>  		if (unlikely(fill_vec_buf_packed(dev, vq,
>  						vq->last_avail_idx, &desc_count,
>  						buf_vec, &nr_vec,
> -						&buf_id, &dummy_len,
> +						&buf_id, &buf_len,
>  						VHOST_ACCESS_RO) < 0))
>  			break;
>  
> @@ -1466,7 +1557,7 @@ virtio_dev_tx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
>  			update_shadow_used_ring_packed(vq, buf_id, 0,
>  					desc_count);
>  
> -		pkts[i] = rte_pktmbuf_alloc(mbuf_pool);
> +		pkts[i] = virtio_dev_pktmbuf_alloc(dev, mbuf_pool, buf_len);
>  		if (unlikely(pkts[i] == NULL)) {
>  			RTE_LOG(ERR, VHOST_DATA,
>  				"Failed to allocate memory for mbuf.\n");
> -- 
> 2.20.1
>