Re: [dpdk-dev] [PATCH v7 1/8] net/virtio: vring init for packed queues

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

On 10/03/2018 03:11 PM, Jens Freimann wrote:
> Add and initialize descriptor data structures.
> 
> To allow out of order processing a .next field was added to
> struct vq_desc_extra because there is none in the packed virtqueue
> descriptor itself. This is used to chain descriptors and process them
> similiar to how it is handled for split virtqueues.
> 
> Signed-off-by: Jens Freimann <jfreimann@redhat.com>
> ---
>   drivers/net/virtio/virtio_ethdev.c | 28 +++++++++------
>   drivers/net/virtio/virtio_pci.h    |  8 +++++
>   drivers/net/virtio/virtio_ring.h   | 55 +++++++++++++++++++++++++++---
>   drivers/net/virtio/virtqueue.h     | 13 ++++++-
>   4 files changed, 88 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
> index b81df0a99..d6a1613dd 100644
> --- a/drivers/net/virtio/virtio_ethdev.c
> +++ b/drivers/net/virtio/virtio_ethdev.c
> @@ -299,19 +299,27 @@ virtio_init_vring(struct virtqueue *vq)
>   
>   	PMD_INIT_FUNC_TRACE();
>   
> -	/*
> -	 * Reinitialise since virtio port might have been stopped and restarted
> -	 */
>   	memset(ring_mem, 0, vq->vq_ring_size);
> -	vring_init(vr, size, ring_mem, VIRTIO_PCI_VRING_ALIGN);
> +	vring_init(vq->hw, vr, size, ring_mem, VIRTIO_PCI_VRING_ALIGN);
> +
> +	vq->vq_free_cnt = vq->vq_nentries;
> +	memset(vq->vq_descx, 0, sizeof(struct vq_desc_extra) * vq->vq_nentries);
>   	vq->vq_used_cons_idx = 0;
> +	vq->vq_avail_idx     = 0;
>   	vq->vq_desc_head_idx = 0;
> -	vq->vq_avail_idx = 0;
>   	vq->vq_desc_tail_idx = (uint16_t)(vq->vq_nentries - 1);
> -	vq->vq_free_cnt = vq->vq_nentries;
> -	memset(vq->vq_descx, 0, sizeof(struct vq_desc_extra) * vq->vq_nentries);
> +	if (vtpci_packed_queue(vq->hw)) {
> +		uint16_t i;
> +		for(i = 0; i < size - 1; i++) {
> +			vq->vq_descx[i].next = i + 1;

I would move it in a dedicated loop, and do it only if IN_ORDER hasn't
been negotiated. Not for performance reason of course, but just to
highlight that this extra stuff isn't needed with in-order.

> +			vq->vq_ring.desc_packed[i].index = i;

I would use the vring_desc_init_packed function declared below instead.

> +		}

Trailing space.

> +		vq->vq_ring.desc_packed[i].index = i;
> +		vq->vq_descx[i].next = VQ_RING_DESC_CHAIN_END;
> +	} else {
>   
> -	vring_desc_init(vr->desc, size);
> +		vring_desc_init_split(vr->desc, size);
> +	}
>   
>   	/*
>   	 * Disable device(host) interrupting guest
> @@ -386,7 +394,7 @@ virtio_init_queue(struct rte_eth_dev *dev, uint16_t vtpci_queue_idx)
>   	/*
>   	 * Reserve a memzone for vring elements
>   	 */
> -	size = vring_size(vq_size, VIRTIO_PCI_VRING_ALIGN);
> +	size = vring_size(hw, vq_size, VIRTIO_PCI_VRING_ALIGN);
>   	vq->vq_ring_size = RTE_ALIGN_CEIL(size, VIRTIO_PCI_VRING_ALIGN);
>   	PMD_INIT_LOG(DEBUG, "vring_size: %d, rounded_vring_size: %d",
>   		     size, vq->vq_ring_size);
> @@ -489,7 +497,7 @@ virtio_init_queue(struct rte_eth_dev *dev, uint16_t vtpci_queue_idx)
>   		for (i = 0; i < vq_size; i++) {
>   			struct vring_desc *start_dp = txr[i].tx_indir;
>   
> -			vring_desc_init(start_dp, RTE_DIM(txr[i].tx_indir));
> +			vring_desc_init_split(start_dp, RTE_DIM(txr[i].tx_indir));
>   
>   			/* first indirect descriptor is always the tx header */
>   			start_dp->addr = txvq->virtio_net_hdr_mem
> diff --git a/drivers/net/virtio/virtio_pci.h b/drivers/net/virtio/virtio_pci.h
> index 58fdd3d45..90204d281 100644
> --- a/drivers/net/virtio/virtio_pci.h
> +++ b/drivers/net/virtio/virtio_pci.h
> @@ -113,6 +113,8 @@ struct virtnet_ctl;
>   
>   #define VIRTIO_F_VERSION_1		32
>   #define VIRTIO_F_IOMMU_PLATFORM	33
> +#define VIRTIO_F_RING_PACKED		34
> +#define VIRTIO_F_IN_ORDER		35
Isn't that feature already declared?

>   
>   /*
>    * Some VirtIO feature bits (currently bits 28 through 31) are
> @@ -314,6 +316,12 @@ vtpci_with_feature(struct virtio_hw *hw, uint64_t bit)
>   	return (hw->guest_features & (1ULL << bit)) != 0;
>   }
>   
> +static inline int
> +vtpci_packed_queue(struct virtio_hw *hw)
> +{
> +	return vtpci_with_feature(hw, VIRTIO_F_RING_PACKED);
> +}
> +
>   /*
>    * Function declaration from virtio_pci.c
>    */
> diff --git a/drivers/net/virtio/virtio_ring.h b/drivers/net/virtio/virtio_ring.h
> index 9e3c2a015..309069fdb 100644
> --- a/drivers/net/virtio/virtio_ring.h
> +++ b/drivers/net/virtio/virtio_ring.h
> @@ -54,11 +54,38 @@ struct vring_used {
>   	struct vring_used_elem ring[0];
>   };
>   
> +/* For support of packed virtqueues in Virtio 1.1 the format of descriptors
> + * looks like this.
> + */
> +struct vring_desc_packed {
> +	uint64_t addr;
> +	uint32_t len;
> +	uint16_t index;
> +	uint16_t flags;
> +} __attribute__ ((aligned(16)));
> +
> +#define RING_EVENT_FLAGS_ENABLE 0x0
> +#define RING_EVENT_FLAGS_DISABLE 0x1
> +#define RING_EVENT_FLAGS_DESC 0x2
> +struct vring_packed_desc_event {
> +	uint16_t desc_event_off_wrap;
> +	uint16_t desc_event_flags;
> +};
> +
>   struct vring {
>   	unsigned int num;
> -	struct vring_desc  *desc;
> -	struct vring_avail *avail;
> -	struct vring_used  *used;
> +	union {
> +		struct vring_desc_packed *desc_packed;
> +		struct vring_desc *desc;
> +	};
> +	union {
> +		struct vring_avail *avail;
> +		struct vring_packed_desc_event *driver_event;
> +	};
> +	union {
> +		struct vring_used  *used;
> +		struct vring_packed_desc_event *device_event;
> +	};
>   };
>   
>   /* The standard layout for the ring is a continuous chunk of memory which
> @@ -95,10 +122,18 @@ struct vring {
>   #define vring_avail_event(vr) (*(uint16_t *)&(vr)->used->ring[(vr)->num])
>   
>   static inline size_t
> -vring_size(unsigned int num, unsigned long align)
> +vring_size(struct virtio_hw *hw, unsigned int num, unsigned long align)
>   {
>   	size_t size;
>   
> +	if (vtpci_packed_queue(hw)) {
> +		size = num * sizeof(struct vring_desc_packed);
> +		size += sizeof(struct vring_packed_desc_event);
> +		size = RTE_ALIGN_CEIL(size, align);
> +		size += sizeof(struct vring_packed_desc_event);
> +		return size;
> +	}
> +
>   	size = num * sizeof(struct vring_desc);
>   	size += sizeof(struct vring_avail) + (num * sizeof(uint16_t));
>   	size = RTE_ALIGN_CEIL(size, align);
> @@ -108,10 +143,20 @@ vring_size(unsigned int num, unsigned long align)
>   }
>   
>   static inline void
> -vring_init(struct vring *vr, unsigned int num, uint8_t *p,
> +vring_init(struct virtio_hw *hw, struct vring *vr, unsigned int num, uint8_t *p,
>   	unsigned long align)
>   {
>   	vr->num = num;
> +	if (vtpci_packed_queue(hw)) {
> +		vr->desc_packed = (struct vring_desc_packed *)p;
> +		vr->driver_event = (struct vring_packed_desc_event *)(p +
> +			num * sizeof(struct vring_desc_packed));
> +		vr->device_event = (struct vring_packed_desc_event *)
> +				RTE_ALIGN_CEIL((uintptr_t)(vr->driver_event +
> +				sizeof(struct vring_packed_desc_event)), align);
> +		return;
> +	}
> +

As a general comment, I would find it cleaner to have dedicated
functions for split and packed variants, like vring_init_split,
vring_init_packed, etc...


>   	vr->desc = (struct vring_desc *) p;
>   	vr->avail = (struct vring_avail *) (p +
>   		num * sizeof(struct vring_desc));
> diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
> index 26518ed98..6a4f92b79 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -161,6 +161,7 @@ struct virtio_pmd_ctrl {
>   struct vq_desc_extra {
>   	void *cookie;
>   	uint16_t ndescs;
> +	uint16_t next;
>   };
>   
>   struct virtqueue {
> @@ -245,9 +246,19 @@ struct virtio_tx_region {
>   			   __attribute__((__aligned__(16)));
>   };
>   
> +static inline void
> +vring_desc_init_packed(struct vring *vr, int n)
> +{
> +	int i;
> +	for (i = 0; i < n; i++) {
> +		struct vring_desc_packed *desc = &vr->desc_packed[i];
> +		desc->index = i;
> +	}
> +}

I see the split variant is also called to init the indirect tables.
Do you confirm this isn't needed in the case of packed ring?

> +
>   /* Chain all the descriptors in the ring with an END */
>   static inline void
> -vring_desc_init(struct vring_desc *dp, uint16_t n)
> +vring_desc_init_split(struct vring_desc *dp, uint16_t n)
>   {
>   	uint16_t i;
>   
>