Re: [dpdk-dev] [PATCH v4] vhost: support inflight share memory protocol feature

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

On 5/5/19 11:02 AM, Li Lin wrote:
> From: Li Lin <lilin24@baidu.com>
> 
> This patch introduces two new messages VHOST_USER_GET_INFLIGHT_FD
> and VHOST_USER_SET_INFLIGHT_FD to support transferring a shared
> buffer between qemu and backend.
> 
> Firstly, qemu uses VHOST_USER_GET_INFLIGHT_FD to get the
> shared buffer from backend. Then qemu should send it back
> through VHOST_USER_SET_INFLIGHT_FD each time we start vhost-user.
> 
> This shared buffer is used to process inflight I/O when backend
> reconnect.
> 
> Signed-off-by: Li Lin <lilin24@baidu.com>
> Signed-off-by: Ni Xun <nixun@baidu.com>
> Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
> ---
> v2 - add set&clr inflight desc functions
> v3 - simplified some functions implementation
> v4 - rework some data structures according to qemu doc
> 
>   lib/librte_vhost/rte_vhost.h           |  83 ++++++++++
>   lib/librte_vhost/rte_vhost_version.map |   3 +
>   lib/librte_vhost/vhost.c               | 105 ++++++++++++
>   lib/librte_vhost/vhost.h               |  12 ++
>   lib/librte_vhost/vhost_user.c          | 292 +++++++++++++++++++++++++++++++++
>   lib/librte_vhost/vhost_user.h          |  13 +-
>   6 files changed, 507 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_vhost/rte_vhost.h b/lib/librte_vhost/rte_vhost.h
> index d2c0c93f4..d4d709717 100644
> --- a/lib/librte_vhost/rte_vhost.h
> +++ b/lib/librte_vhost/rte_vhost.h
> @@ -71,6 +71,10 @@ extern "C" {
>   #define VHOST_USER_PROTOCOL_F_HOST_NOTIFIER 11
>   #endif
>   
> +#ifndef VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD
> +#define VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD 12
> +#endif
> +
>   /** Indicate whether protocol features negotiation is supported. */
>   #ifndef VHOST_USER_F_PROTOCOL_FEATURES
>   #define VHOST_USER_F_PROTOCOL_FEATURES	30
> @@ -98,12 +102,41 @@ struct rte_vhost_memory {
>   	struct rte_vhost_mem_region regions[];
>   };
>   
> +struct inflight_desc {
> +	uint8_t inflight;
> +	uint8_t padding[5];
> +	uint16_t next;
> +	uint64_t counter;
> +};
> +
> +struct inflight_info {
> +	uint64_t features;
> +	uint16_t version;
> +	uint16_t desc_num;
> +	uint16_t last_inflight_io;
> +	uint16_t used_idx;
> +	struct inflight_desc desc[0];
> +};
> +
> +struct resubmit_desc {
> +	uint16_t index;
> +	uint64_t counter;
> +};
> +
> +struct resubmit_info {
> +	struct resubmit_desc *resubmit_list;
> +	uint16_t resubmit_num;
> +};
> +
>   struct rte_vhost_vring {
>   	struct vring_desc	*desc;
>   	struct vring_avail	*avail;
>   	struct vring_used	*used;
>   	uint64_t		log_guest_addr;
>   
> +	struct inflight_info	*inflight;
> +	struct resubmit_info	*resubmit;
> +
>   	/** Deprecated, use rte_vhost_vring_call() instead. */
>   	int			callfd;
>   
> @@ -632,6 +665,56 @@ int rte_vhost_get_vhost_vring(int vid, uint16_t vring_idx,
>   int rte_vhost_vring_call(int vid, uint16_t vring_idx);
>   
>   /**
> + * set inflight flag for a desc.
> + *
> + * @param vid
> + *  vhost device ID
> + * @param vring_idx
> + *  vring index
> + * @param idx
> + *  inflight entry index
> + * @return
> + *  0 on success, -1 on failure
> + */
> +int __rte_experimental
> +rte_vhost_set_inflight_desc(int vid, uint16_t vring_idx,
> +		uint16_t idx);
> +
> +/**
> + * clear inflight flag for a desc.
> + *
> + * @param vid
> + *  vhost device ID
> + * @param vring_idx
> + *  vring index
> + * @param last_used_idx
> + *  next free used_idx
> + * @param idx
> + *  inflight entry index
> + * @return
> + *  0 on success, -1 on failure
> + */
> +int __rte_experimental
> +rte_vhost_clr_inflight_desc(int vid, uint16_t vring_idx,
> +		uint16_t last_used_idx, uint16_t idx);
> +
> +/**
> + * set last inflight io index.
> + *
> + * @param vid
> + *  vhost device ID
> + * @param vring_idx
> + *  vring index
> + * @param idx
> + *  inflight entry index
> + * @return
> + *  0 on success, -1 on failure
> + */
> +int __rte_experimental
> +rte_vhost_set_last_inflight_io(int vid, uint16_t vring_idx,
> +		uint16_t idx);
> +
> +/**
>    * Get vhost RX queue avail count.
>    *
>    * @param vid
> diff --git a/lib/librte_vhost/rte_vhost_version.map b/lib/librte_vhost/rte_vhost_version.map
> index 5f1d4a75c..a992b3935 100644
> --- a/lib/librte_vhost/rte_vhost_version.map
> +++ b/lib/librte_vhost/rte_vhost_version.map
> @@ -87,4 +87,7 @@ EXPERIMENTAL {
>   	rte_vdpa_relay_vring_used;
>   	rte_vhost_extern_callback_register;
>   	rte_vhost_driver_set_protocol_features;
> +	rte_vhost_set_inflight_desc;
> +	rte_vhost_clr_inflight_desc;
> +	rte_vhost_set_last_inflight_io;
>   };
> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
> index 163f4595e..03eab3551 100644
> --- a/lib/librte_vhost/vhost.c
> +++ b/lib/librte_vhost/vhost.c
> @@ -76,6 +76,16 @@ cleanup_vq(struct vhost_virtqueue *vq, int destroy)
>   		close(vq->callfd);
>   	if (vq->kickfd >= 0)
>   		close(vq->kickfd);
> +	if (vq->inflight)
> +		vq->inflight = NULL;
> +	if (vq->resubmit->resubmit_list) {
> +		free(vq->resubmit->resubmit_list);
> +		vq->resubmit->resubmit_list = NULL;
> +	}
> +	if (vq->resubmit) {
> +		free(vq->resubmit);
> +		vq->resubmit = NULL;
> +	}
>   }
>   
>   /*
> @@ -589,6 +599,9 @@ rte_vhost_get_vhost_vring(int vid, uint16_t vring_idx,
>   	vring->kickfd  = vq->kickfd;
>   	vring->size    = vq->size;
>   
> +	vring->inflight = vq->inflight;
> +	vring->resubmit = vq->resubmit;
> +
>   	return 0;
>   }
>   
> @@ -617,6 +630,98 @@ rte_vhost_vring_call(int vid, uint16_t vring_idx)
>   	return 0;
>   }
>   
> +int
> +rte_vhost_set_inflight_desc(int vid, uint16_t vring_idx, uint16_t idx)
> +{
> +	struct virtio_net *dev;
> +	struct vhost_virtqueue *vq;
> +
> +	dev = get_device(vid);
> +	if (!dev)
> +		return -1;
> +
> +	if (!(dev->features &
> +		(1ULL << VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)))
> +		return 0;

Shouldn't -1 be returned here also?
I think this function should be called only if the feature negotiation
succeeded.

Returning an error here would help the calling application to know
something went wrong.

Same comment applies for the clear function.
> +
> +	if (vring_idx >= VHOST_MAX_VRING)
> +		return -1;
> +
> +	vq = dev->virtqueue[vring_idx];
> +	if (!vq)
> +		return -1;
> +
> +	if (unlikely(!vq->inflight))
> +		return -1;
> +
> +	vq->inflight->desc[idx].counter = vq->counter++;
> +	vq->inflight->desc[idx].inflight = 1;
> +	return 0;
> +}
> +
> +int
> +rte_vhost_clr_inflight_desc(int vid, uint16_t vring_idx,
> +	uint16_t last_used_idx, uint16_t idx)
> +{
> +	struct virtio_net *dev;
> +	struct vhost_virtqueue *vq;
> +
> +	dev = get_device(vid);
> +	if (!dev)
> +		return -1;
> +
> +	if (!(dev->features &
> +		(1ULL << VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)))
> +		return 0;
> +
> +	if (vring_idx >= VHOST_MAX_VRING)
> +		return -1;
> +
> +	vq = dev->virtqueue[vring_idx];
> +	if (!vq)
> +		return -1;
> +
> +	if (unlikely(!vq->inflight))
> +		return -1;
> +
> +	rte_compiler_barrier();
> +
> +	vq->inflight->desc[idx].inflight = 0;
> +
> +	rte_compiler_barrier();
> +
> +	vq->inflight->used_idx = last_used_idx;
> +	return 0;
> +}
> +
> +int
> +rte_vhost_set_last_inflight_io(int vid, uint16_t vring_idx, uint16_t idx)
> +{
> +	struct virtio_net *dev;
> +	struct vhost_virtqueue *vq;
> +
> +	dev = get_device(vid);
> +	if (!dev)
> +		return -1;
> +
> +	if (!(dev->features &
> +		(1ULL << VHOST_USER_PROTOCOL_F_INFLIGHT_SHMFD)))
> +		return 0;
> +
> +	if (vring_idx >= VHOST_MAX_VRING)
> +		return -1;
> +
> +	vq = dev->virtqueue[vring_idx];
> +	if (!vq)
> +		return -1;
> +
> +	if (unlikely(!vq->inflight))
> +		return -1;
> +
> +	vq->inflight->last_inflight_io = idx;
> +	return 0;
> +}

Are above functions supposed to be called in the hot path?
If so, you might want to use unlikely for the error checks
everywhere.

> +
>   uint16_t
>   rte_vhost_avail_entries(int vid, uint16_t queue_id)
>   {
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index e9138dfab..3dace2ec3 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -128,6 +128,11 @@ struct vhost_virtqueue {
>   	/* Physical address of used ring, for logging */
>   	uint64_t		log_guest_addr;
>   
> +	/* Inflight share memory info */
> +	struct inflight_info	*inflight;
> +	struct resubmit_info	*resubmit;
> +	uint64_t counter;

counter and resubmit are too generic names.

> +
>   	uint16_t		nr_zmbuf;
>   	uint16_t		zmbuf_size;
>   	uint16_t		last_zmbuf_idx;
> @@ -286,6 +291,12 @@ struct guest_page {
>   	uint64_t size;
>   };
>   
> +struct inflight_mem_info {
> +	int fd;
> +	void *addr;
> +	uint64_t size;
> +};
> +
>   /**
>    * Device structure contains all configuration information relating
>    * to the device.
> @@ -303,6 +314,7 @@ struct virtio_net {
>   	uint32_t		nr_vring;
>   	int			dequeue_zero_copy;
>   	struct vhost_virtqueue	*virtqueue[VHOST_MAX_QUEUE_PAIRS * 2];
> +	struct inflight_mem_info inflight_info;
>   #define IF_NAME_SZ (PATH_MAX > IFNAMSIZ ? PATH_MAX : IFNAMSIZ)
>   	char			ifname[IF_NAME_SZ];
>   	uint64_t		log_size;

Do you have some code example using these new APIs?
It would help for reviewing the patch.

Thanks,
Maxime