[dpdk-dev] [1/4] net/virtio: fix the control vq support

[Maxime Coquelin]

On 1/23/19 5:33 PM, Ilya Maximets wrote:
> Hmm. Nevermind.
> Please, ignore my previous comments to this patch.
> Patch seems compliant to spec, but the spec is not very clear.

Ok, thanks for the review and the folluw-up.

Maxime

> Best regards, Ilya Maximets.
> 
> On 23.01.2019 16:09, Ilya Maximets wrote:
>> On 22.01.2019 20:01, Tiwei Bie wrote:
>>> This patch mainly fixed below issues in the packed ring based
>>> control vq support in virtio driver:
>>>
>>> 1. When parsing the used descriptors, we have to track the
>>>     number of descs that we need to skip;
>>> 2. vq->vq_free_cnt was decreased twice for a same desc;
>>>
>>> Meanwhile, make the function name consistent with other parts.
>>>
>>> Fixes: ec194c2f1895 ("net/virtio: support packed queue in send command")
>>> Fixes: a4270ea4ff79 ("net/virtio: check head desc with correct wrap counter")
>>>
>>> Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
>>> ---
>>>   drivers/net/virtio/virtio_ethdev.c | 62 ++++++++++++++----------------
>>>   drivers/net/virtio/virtqueue.h     | 12 +-----
>>>   2 files changed, 31 insertions(+), 43 deletions(-)
>>>
>>> diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
>>> index ee5a98b7c..a3fe65599 100644
>>> --- a/drivers/net/virtio/virtio_ethdev.c
>>> +++ b/drivers/net/virtio/virtio_ethdev.c
>>> @@ -142,16 +142,17 @@ static const struct rte_virtio_xstats_name_off rte_virtio_txq_stat_strings[] = {
>>>   struct virtio_hw_internal virtio_hw_internal[RTE_MAX_ETHPORTS];
>>>   
>>>   static struct virtio_pmd_ctrl *
>>> -virtio_pq_send_command(struct virtnet_ctl *cvq, struct virtio_pmd_ctrl *ctrl,
>>> -		       int *dlen, int pkt_num)
>>> +virtio_send_command_packed(struct virtnet_ctl *cvq,
>>> +			   struct virtio_pmd_ctrl *ctrl,
>>> +			   int *dlen, int pkt_num)
>>>   {
>>>   	struct virtqueue *vq = cvq->vq;
>>>   	int head;
>>>   	struct vring_packed_desc *desc = vq->ring_packed.desc_packed;
>>>   	struct virtio_pmd_ctrl *result;
>>> -	bool avail_wrap_counter, used_wrap_counter;
>>> -	uint16_t flags;
>>> +	bool avail_wrap_counter;
>>>   	int sum = 0;
>>> +	int nb_descs = 0;
>>>   	int k;
>>>   
>>>   	/*
>>> @@ -162,11 +163,10 @@ virtio_pq_send_command(struct virtnet_ctl *cvq, struct virtio_pmd_ctrl *ctrl,
>>>   	 */
>>>   	head = vq->vq_avail_idx;
>>>   	avail_wrap_counter = vq->avail_wrap_counter;
>>> -	used_wrap_counter = vq->used_wrap_counter;
>>> -	desc[head].flags = VRING_DESC_F_NEXT;
>>>   	desc[head].addr = cvq->virtio_net_hdr_mem;
>>>   	desc[head].len = sizeof(struct virtio_net_ctrl_hdr);
>>>   	vq->vq_free_cnt--;
>>> +	nb_descs++;
>>>   	if (++vq->vq_avail_idx >= vq->vq_nentries) {
>>>   		vq->vq_avail_idx -= vq->vq_nentries;
>>>   		vq->avail_wrap_counter ^= 1;
>>> @@ -177,55 +177,51 @@ virtio_pq_send_command(struct virtnet_ctl *cvq, struct virtio_pmd_ctrl *ctrl,
>>>   			+ sizeof(struct virtio_net_ctrl_hdr)
>>>   			+ sizeof(ctrl->status) + sizeof(uint8_t) * sum;
>>>   		desc[vq->vq_avail_idx].len = dlen[k];
>>> -		flags = VRING_DESC_F_NEXT;
>>
>> Looks like barriers was badly placed here before this patch.
>> Anyway, you need a write barrier here between {addr, len} and flags updates.
>>
>>> +		desc[vq->vq_avail_idx].flags = VRING_DESC_F_NEXT |
>>> +			VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
>>> +			VRING_DESC_F_USED(!vq->avail_wrap_counter);
>>>   		sum += dlen[k];
>>>   		vq->vq_free_cnt--;
>>> -		flags |= VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
>>> -			 VRING_DESC_F_USED(!vq->avail_wrap_counter);
>>> -		desc[vq->vq_avail_idx].flags = flags;
>>> -		rte_smp_wmb();
>>> -		vq->vq_free_cnt--;
>>> +		nb_descs++;
>>>   		if (++vq->vq_avail_idx >= vq->vq_nentries) {
>>>   			vq->vq_avail_idx -= vq->vq_nentries;
>>>   			vq->avail_wrap_counter ^= 1;
>>>   		}
>>>   	}
>>>   
>>> -
>>>   	desc[vq->vq_avail_idx].addr = cvq->virtio_net_hdr_mem
>>>   		+ sizeof(struct virtio_net_ctrl_hdr);
>>>   	desc[vq->vq_avail_idx].len = sizeof(ctrl->status);
>>> -	flags = VRING_DESC_F_WRITE;
>>> -	flags |= VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
>>> -		 VRING_DESC_F_USED(!vq->avail_wrap_counter);
>>> -	desc[vq->vq_avail_idx].flags = flags;
>>> -	flags = VRING_DESC_F_NEXT;
>>> -	flags |= VRING_DESC_F_AVAIL(avail_wrap_counter) |
>>> -		 VRING_DESC_F_USED(!avail_wrap_counter);
>>> -	desc[head].flags = flags;
>>> -	rte_smp_wmb();
>>> -
>>
>> Same here. We need a write barrier to be sure that {addr, len} written
>> before updating flags.
>>
>> Another way to avoid most of barriers is to work similar to
>> 'flush_shadow_used_ring_packed',
>> i.e. update all the data in a loop - write barrier - update all the flags.
>>
>>> +	desc[vq->vq_avail_idx].flags = VRING_DESC_F_WRITE |
>>> +		VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
>>> +		VRING_DESC_F_USED(!vq->avail_wrap_counter);
>>>   	vq->vq_free_cnt--;
>>> +	nb_descs++;
>>>   	if (++vq->vq_avail_idx >= vq->vq_nentries) {
>>>   		vq->vq_avail_idx -= vq->vq_nentries;
>>>   		vq->avail_wrap_counter ^= 1;
>>>   	}
>>>   
>>> +	virtio_wmb(vq->hw->weak_barriers);
>>> +	desc[head].flags = VRING_DESC_F_NEXT |
>>> +		VRING_DESC_F_AVAIL(avail_wrap_counter) |
>>> +		VRING_DESC_F_USED(!avail_wrap_counter);
>>> +
>>> +	virtio_wmb(vq->hw->weak_barriers);
>>>   	virtqueue_notify(vq);
>>>   
>>>   	/* wait for used descriptors in virtqueue */
>>> -	do {
>>> -		rte_rmb();
>>> +	while (!desc_is_used(&desc[head], vq))
>>>   		usleep(100);
>>> -	} while (!__desc_is_used(&desc[head], used_wrap_counter));
>>> +
>>> +	virtio_rmb(vq->hw->weak_barriers);
>>>   
>>>   	/* now get used descriptors */
>>> -	while (desc_is_used(&desc[vq->vq_used_cons_idx], vq)) {
>>> -		vq->vq_free_cnt++;
>>> -		if (++vq->vq_used_cons_idx >= vq->vq_nentries) {
>>> -			vq->vq_used_cons_idx -= vq->vq_nentries;
>>> -			vq->used_wrap_counter ^= 1;
>>> -		}
>>> +	vq->vq_free_cnt += nb_descs;
>>> +	vq->vq_used_cons_idx += nb_descs;
>>> +	if (vq->vq_used_cons_idx >= vq->vq_nentries) {
>>> +		vq->vq_used_cons_idx -= vq->vq_nentries;
>>> +		vq->used_wrap_counter ^= 1;
>>>   	}
>>>   
>>>   	result = cvq->virtio_net_hdr_mz->addr;
>>> @@ -266,7 +262,7 @@ virtio_send_command(struct virtnet_ctl *cvq, struct virtio_pmd_ctrl *ctrl,
>>>   		sizeof(struct virtio_pmd_ctrl));
>>>   
>>>   	if (vtpci_packed_queue(vq->hw)) {
>>> -		result = virtio_pq_send_command(cvq, ctrl, dlen, pkt_num);
>>> +		result = virtio_send_command_packed(cvq, ctrl, dlen, pkt_num);
>>>   		goto out_unlock;
>>>   	}
>>>   
>>> diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
>>> index 7fcde5643..ca9d8e6e3 100644
>>> --- a/drivers/net/virtio/virtqueue.h
>>> +++ b/drivers/net/virtio/virtqueue.h
>>> @@ -281,7 +281,7 @@ struct virtio_tx_region {
>>>   };
>>>   
>>>   static inline int
>>> -__desc_is_used(struct vring_packed_desc *desc, bool wrap_counter)
>>> +desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq)
>>>   {
>>>   	uint16_t used, avail, flags;
>>>   
>>> @@ -289,16 +289,9 @@ __desc_is_used(struct vring_packed_desc *desc, bool wrap_counter)
>>>   	used = !!(flags & VRING_DESC_F_USED(1));
>>>   	avail = !!(flags & VRING_DESC_F_AVAIL(1));
>>>   
>>> -	return avail == used && used == wrap_counter;
>>> +	return avail == used && used == vq->used_wrap_counter;
>>>   }
>>>   
>>> -static inline int
>>> -desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq)
>>> -{
>>> -	return __desc_is_used(desc, vq->used_wrap_counter);
>>> -}
>>> -
>>> -
>>>   static inline void
>>>   vring_desc_init_packed(struct virtqueue *vq, int n)
>>>   {
>>> @@ -354,7 +347,6 @@ virtqueue_enable_intr_packed(struct virtqueue *vq)
>>>   {
>>>   	uint16_t *event_flags = &vq->ring_packed.driver_event->desc_event_flags;
>>>   
>>> -
>>>   	if (vq->event_flags_shadow == RING_EVENT_FLAGS_DISABLE) {
>>>   		virtio_wmb(vq->hw->weak_barriers);
>>>   		vq->event_flags_shadow = RING_EVENT_FLAGS_ENABLE;
>>>