[dpdk-dev] [PATCH v5 5/6] vhost: batch update used ring

[Maxime Coquelin]

On 09/14/2016 10:43 AM, Wang, Zhihong wrote:
>
>
>> -----Original Message-----
>> From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com]
>> Sent: Monday, September 12, 2016 11:46 PM
>> To: Wang, Zhihong <zhihong.wang at intel.com>; dev at dpdk.org
>> Cc: yuanhan.liu at linux.intel.com; thomas.monjalon at 6wind.com
>> Subject: Re: [PATCH v5 5/6] vhost: batch update used ring
>>
>>
>>
>> On 09/09/2016 05:39 AM, Zhihong Wang wrote:
>>> This patch enables batch update of the used ring for better efficiency.
>>>
>>> Signed-off-by: Zhihong Wang <zhihong.wang at intel.com>
>>> ---
>>> Changes in v4:
>>>
>>>  1. Free shadow used ring in the right place.
>>>
>>>  2. Add failure check for shadow used ring malloc.
>>>
>>>  lib/librte_vhost/vhost.c      | 20 ++++++++++++--
>>>  lib/librte_vhost/vhost.h      |  4 +++
>>>  lib/librte_vhost/vhost_user.c | 31 +++++++++++++++++----
>>>  lib/librte_vhost/virtio_net.c | 64
>> +++++++++++++++++++++++++++++++++++--------
>>>  4 files changed, 101 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c
>>> index 46095c3..cb31cdd 100644
>>> --- a/lib/librte_vhost/vhost.c
>>> +++ b/lib/librte_vhost/vhost.c
>>> @@ -119,10 +119,26 @@ cleanup_device(struct virtio_net *dev, int
>> destroy)
>>>  static void
>>>  free_device(struct virtio_net *dev)
>>>  {
>>> +	struct vhost_virtqueue *vq_0;
>>> +	struct vhost_virtqueue *vq_1;
>>>  	uint32_t i;
>>>
>>> -	for (i = 0; i < dev->virt_qp_nb; i++)
>>> -		rte_free(dev->virtqueue[i * VIRTIO_QNUM]);
>>> +	for (i = 0; i < dev->virt_qp_nb; i++) {
>>> +		vq_0 = dev->virtqueue[i * VIRTIO_QNUM];
>>> +		if (vq_0->shadow_used_ring) {
>>> +			rte_free(vq_0->shadow_used_ring);
>>> +			vq_0->shadow_used_ring = NULL;
>>> +		}
>>> +
>>> +		vq_1 = dev->virtqueue[i * VIRTIO_QNUM + 1];
>>> +		if (vq_1->shadow_used_ring) {
>>> +			rte_free(vq_1->shadow_used_ring);
>>> +			vq_1->shadow_used_ring = NULL;
>>> +		}
>>> +
>>> +		/* malloc together, free together */
>>> +		rte_free(vq_0);
>>> +	}
>>>
>>>  	rte_free(dev);
>>>  }
>>> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
>>> index 9707dfc..381dc27 100644
>>> --- a/lib/librte_vhost/vhost.h
>>> +++ b/lib/librte_vhost/vhost.h
>>> @@ -85,6 +85,10 @@ struct vhost_virtqueue {
>>>
>>>  	/* Physical address of used ring, for logging */
>>>  	uint64_t		log_guest_addr;
>>> +
>>> +	/* Shadow used ring for performance */
>>> +	struct vring_used_elem	*shadow_used_ring;
>>> +	uint32_t		shadow_used_idx;
>>>  } __rte_cache_aligned;
>>>
>>>  /* Old kernels have no such macro defined */
>>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>>> index eee99e9..d7cf1ed 100644
>>> --- a/lib/librte_vhost/vhost_user.c
>>> +++ b/lib/librte_vhost/vhost_user.c
>>> @@ -193,7 +193,21 @@ static int
>>>  vhost_user_set_vring_num(struct virtio_net *dev,
>>>  			 struct vhost_vring_state *state)
>>>  {
>>> -	dev->virtqueue[state->index]->size = state->num;
>>> +	struct vhost_virtqueue *vq;
>>> +
>>> +	vq = dev->virtqueue[state->index];
>>> +	vq->size = state->num;
>>> +	if (!vq->shadow_used_ring) {
>>> +		vq->shadow_used_ring = rte_malloc(NULL,
>>> +				vq->size * sizeof(struct vring_used_elem),
>>> +				RTE_CACHE_LINE_SIZE);
>>> +		if (!vq->shadow_used_ring) {
>>> +			RTE_LOG(ERR, VHOST_CONFIG,
>>> +				"Failed to allocate memory"
>>> +				" for shadow used ring.\n");
>>> +			return -1;
>>> +		}
>>> +	}
>>>
>>>  	return 0;
>>>  }
>>> @@ -611,14 +625,21 @@ static int
>>>  vhost_user_get_vring_base(struct virtio_net *dev,
>>>  			  struct vhost_vring_state *state)
>>>  {
>>> +	struct vhost_virtqueue *vq;
>>> +
>>>  	/* We have to stop the queue (virtio) if it is running. */
>>>  	if (dev->flags & VIRTIO_DEV_RUNNING) {
>>>  		dev->flags &= ~VIRTIO_DEV_RUNNING;
>>>  		notify_ops->destroy_device(dev->vid);
>>>  	}
>>>
>>> +	vq = dev->virtqueue[state->index];
>>>  	/* Here we are safe to get the last used index */
>>> -	state->num = dev->virtqueue[state->index]->last_used_idx;
>>> +	state->num = vq->last_used_idx;
>>> +	if (vq->shadow_used_ring) {
>>> +		rte_free(vq->shadow_used_ring);
>>> +		vq->shadow_used_ring = NULL;
>>> +	}
>>>
>>>  	RTE_LOG(INFO, VHOST_CONFIG,
>>>  		"vring base idx:%d file:%d\n", state->index, state->num);
>>> @@ -627,10 +648,10 @@ vhost_user_get_vring_base(struct virtio_net
>> *dev,
>>>  	 * sent and only sent in vhost_vring_stop.
>>>  	 * TODO: cleanup the vring, it isn't usable since here.
>>>  	 */
>>> -	if (dev->virtqueue[state->index]->kickfd >= 0)
>>> -		close(dev->virtqueue[state->index]->kickfd);
>>> +	if (vq->kickfd >= 0)
>>> +		close(vq->kickfd);
>>>
>>> -	dev->virtqueue[state->index]->kickfd =
>> VIRTIO_UNINITIALIZED_EVENTFD;
>>> +	vq->kickfd = VIRTIO_UNINITIALIZED_EVENTFD;
>>>
>>>  	return 0;
>>>  }
>>> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
>>> index b38f18f..e9f6353 100644
>>> --- a/lib/librte_vhost/virtio_net.c
>>> +++ b/lib/librte_vhost/virtio_net.c
>>> @@ -134,17 +134,52 @@ virtio_enqueue_offload(struct rte_mbuf
>> *m_buf, struct virtio_net_hdr *net_hdr)
>>>  }
>>>
>>>  static inline void __attribute__((always_inline))
>>> -update_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
>>> -		uint32_t desc_chain_head, uint32_t desc_chain_len)
>>> +update_used_ring(struct vhost_virtqueue *vq, uint32_t
>> desc_chain_head,
>>> +		uint32_t desc_chain_len)
>>>  {
>>> -	uint32_t used_idx = vq->last_used_idx & (vq->size - 1);
>>> -
>>> -	vq->used->ring[used_idx].id = desc_chain_head;
>>> -	vq->used->ring[used_idx].len = desc_chain_len;
>>> +	vq->shadow_used_ring[vq->shadow_used_idx].id  =
>> desc_chain_head;
>>> +	vq->shadow_used_ring[vq->shadow_used_idx].len =
>> desc_chain_len;
>>> +	vq->shadow_used_idx++;
>>>  	vq->last_used_idx++;
>>> -	vhost_log_used_vring(dev, vq, offsetof(struct vring_used,
>>> -				ring[used_idx]),
>>> -			sizeof(vq->used->ring[used_idx]));
>>> +}
>>> +
>>> +static inline void __attribute__((always_inline))
>>> +flush_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
>>> +		uint32_t used_idx_start)
>>> +{
>>> +	if (used_idx_start + vq->shadow_used_idx < vq->size) {
>>> +		rte_memcpy(&vq->used->ring[used_idx_start],
>>> +				&vq->shadow_used_ring[0],
>>> +				vq->shadow_used_idx *
>>> +				sizeof(struct vring_used_elem));
>>> +		vhost_log_used_vring(dev, vq,
>>> +				offsetof(struct vring_used,
>>> +					ring[used_idx_start]),
>>> +				vq->shadow_used_idx *
>>> +				sizeof(struct vring_used_elem));
>>> +	} else {
>>> +		uint32_t part_1 = vq->size - used_idx_start;
>>> +		uint32_t part_2 = vq->shadow_used_idx - part_1;
>>> +
>>> +		rte_memcpy(&vq->used->ring[used_idx_start],
>>> +				&vq->shadow_used_ring[0],
>>> +				part_1 *
>>> +				sizeof(struct vring_used_elem));
>>> +		vhost_log_used_vring(dev, vq,
>>> +				offsetof(struct vring_used,
>>> +					ring[used_idx_start]),
>>> +				part_1 *
>>> +				sizeof(struct vring_used_elem));
>>> +		rte_memcpy(&vq->used->ring[0],
>>> +				&vq->shadow_used_ring[part_1],
>>> +				part_2 *
>>> +				sizeof(struct vring_used_elem));
>>> +		vhost_log_used_vring(dev, vq,
>>> +				offsetof(struct vring_used,
>>> +					ring[0]),
>>> +				part_2 *
>>> +				sizeof(struct vring_used_elem));
>>> +	}
>>>  }
>> Is expanding the code done for performance purpose?
>
> Hi Maxime,
>
> Yes theoretically this has the least branch number.
> And I think the logic is simpler this way.
Ok, in that case, maybe you could create a function to
do the rte_memcpy and the vhost_log_used on a given range.

I don't have a strong opinion on this, if Yuanhan is fine
with current code, that's ok for me.
Thanks,
Maxime
>
> Thanks
> Zhihong
>
>> Or maybe we could have a loop to do that?
>> Something like this (not compiled, not tested):
>>
>> static inline void __attribute__((always_inline))
>> flush_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
>> {
>> 	uint32_t to = used_idx_start;
>> 	uint32_t from = 0;
>> 	uint32_t count;
>>
>> 	if (used_idx_start + vq->shadow_used_idx < vq->size)
>> 		count = vq->shadow_used_idx;
>> 	else
>> 		count = vq->size - used_idx_start;
>>
>> 	do {
>> 		rte_memcpy(&vq->used->ring[to],
>> 				&vq->shadow_used_ring[from],
>> 				count * sizeof(struct vring_used_elem));
>> 		vhost_log_used_vring(dev, vq,
>> 				offsetof(struct vring_used, ring[to]),
>> 				count * sizeof(struct vring_used_elem));
>>
>> 		to = (to + count) & (vq->size - 1);
>> 		from += count;
>> 		count = vq->shadow_used_idx - count;
>> 	} while (count);
>> }
>>
>> Regards,
>> Maxime