On Fri, Dec 11, 2015 at 10:55:48PM -0800, Rich Lane wrote:
> On Wed, Dec 2, 2015 at 10:06 PM, Yuanhan Liu <yuanhan.liu at linux.intel.com>
> wrote:
>
> +static inline struct rte_mbuf *
> +copy_desc_to_mbuf(struct virtio_net *dev, struct vhost_virtqueue *vq,
> +? ? ? ? ? ? ? ? ?uint16_t desc_idx, struct rte_mempool *mbuf_pool)
> +{
>
> ...?
>
> +
> +? ? ? ?desc = &vq->desc[desc_idx];
> +? ? ? ?desc_addr = gpa_to_vva(dev, desc->addr);
> +? ? ? ?rte_prefetch0((void *)(uintptr_t)desc_addr);
> +
> +? ? ? ?/* Discard virtio header */
> +? ? ? ?desc_avail? = desc->len - vq->vhost_hlen;
>
>
> If desc->len is zero (happens all the time when restarting DPDK apps in the
> guest) then desc_avail will be huge.
I'm aware of it; I have already noted that in the cover letter. This
patch set is just a code refactor. Things like that will do a in a
latter patch set. (The thing is that Huawei is very cagy about making
any changes to vhost rxtx code, as it's the hot data path. So, I will
not make any future changes base on this refactor, unless it's applied).
> ?
>
> +? ? ? ?desc_offset = vq->vhost_hlen;
> +
> +? ? ? ?mbuf_avail? = 0;
> +? ? ? ?mbuf_offset = 0;
> +? ? ? ?while (desc_avail || (desc->flags & VRING_DESC_F_NEXT) != 0) {?
>
> +? ? ? ? ? ? ? ?/* This desc reachs to its end, get the next one */
> +? ? ? ? ? ? ? ?if (desc_avail == 0) {
> +? ? ? ? ? ? ? ? ? ? ? ?desc = &vq->desc[desc->next];
>
>
> Need to check desc->next against vq->size.
Thanks for the remind.
>
> There should be a limit on the number of descriptors in a chain to prevent an
> infinite loop.
>
>
> ?uint16_t
> ?rte_vhost_dequeue_burst(struct virtio_net *dev, uint16_t queue_id,
> ? ? ? ? struct rte_mempool *mbuf_pool, struct rte_mbuf **pkts, uint16_t
> count)
> ?{
> ...
> ? ? ? ? avail_idx =? *((volatile uint16_t *)&vq->avail->idx);
> -
> -? ? ? ?/* If there are no available buffers then return. */
> -? ? ? ?if (vq->last_used_idx == avail_idx)
> +? ? ? ?free_entries = avail_idx - vq->last_used_idx;
> +? ? ? ?if (free_entries == 0)
> ? ? ? ? ? ? ? ? return 0;
>
>
> A common problem is that avail_idx goes backwards when the guest zeroes its
> virtqueues. This function could check for free_entries > vq->size and reset
> vq->last_used_idx.
Thanks, but ditto, will consider it in another patch set.
>
>
> +? ? ? ?LOG_DEBUG(VHOST_DATA, "(%"PRIu64") about to dequene %u buffers\n",
> +? ? ? ? ? ? ? ? ? ? ? ?dev->device_fh, count);
>
>
> Typo at "dequene".
Oops; thanks.
--yliu
