Re: [dpdk-dev] [PATCH] vhost: add support to large linear mbufs

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Flavio,

On 10/2/19 12:19 AM, 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, change the API so that the application can
> optionally provide a second mempool containing larger mbufs. If that
> is not provided (NULL), the behavior remains as before the change.
> Otherwise, the data size is checked and the corresponding mempool
> is used to return linear mbufs.

It is not necessary to break the API (and it would require a deprecation
notice), but instead you could create a new API:

static inline uint16_t
vhost_dequeue_burst(int vid, uint16_t queue_id,
		struct rte_mempool *mbuf_pool,
		struct rte_mempool *mbuf_pool_large,
		struct rte_mbuf **pkts, uint16_t count);

uint16_t rte_vhost_dequeue_burst(int vid, uint16_t queue_id,
				struct rte_mempool *mbuf_pool,
				struct rte_mbuf **pkts, uint16_t count)
{
	return vhost_dequeue_burst(vid, queue_id, mbuf_pool, NULL,
				pkts, count);
}

uint16_t rte_vhost_dequeue_burst2(int vid, uint16_t queue_id,
				struct rte_mempool *mbuf_pool,
				struct rte_mempool *mbuf_pool_large,
				struct rte_mbuf **pkts, uint16_t count)
{
	return vhost_dequeue_burst(vid, queue_id, mbuf_pool,
				mbuf_pool_large,
				pkts, count);
}



Yeah, the name isn't very creative, I'm sure you'll have better idea!

> 
> Signed-off-by: Flavio Leitner <fbl@sysclose.org>
> ---
>  drivers/net/vhost/rte_eth_vhost.c |  4 +--
>  examples/tep_termination/main.c   |  2 +-
>  examples/vhost/main.c             |  2 +-
>  lib/librte_vhost/rte_vhost.h      |  5 ++-
>  lib/librte_vhost/virtio_net.c     | 57 +++++++++++++++++++++++--------
>  5 files changed, 50 insertions(+), 20 deletions(-)

Maxime