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To: Jens Freimann <jfreimann@redhat.com>, dev@dpdk.org
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From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Subject: Re: [dpdk-dev] [PATCH v5 03/11] net/virtio: add packed virtqueue
helpers
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On 09/06/2018 08:19 PM, Jens Freimann wrote:
> Add helper functions to set/clear and check descriptor flags.
>
> Signed-off-by: Jens Freimann <jfreimann@redhat.com>
> ---
> drivers/net/virtio/virtio_ring.h | 26 ++++++++++++++++++++++++++
> drivers/net/virtio/virtqueue.h | 19 +++++++++++++++++++
> 2 files changed, 45 insertions(+)
>
> diff --git a/drivers/net/virtio/virtio_ring.h b/drivers/net/virtio/virtio_ring.h
> index e2c597434..f3b23f419 100644
> --- a/drivers/net/virtio/virtio_ring.h
> +++ b/drivers/net/virtio/virtio_ring.h
> @@ -78,6 +78,8 @@ struct vring_packed_desc_event {
>
> struct vring {
> unsigned int num;
> + unsigned int avail_wrap_counter;
> + unsigned int used_wrap_counter;
> union {
> struct vring_desc_packed *desc_packed;
> struct vring_desc *desc;
> @@ -92,6 +94,30 @@ struct vring {
> };
> };
>
> +static inline void
> +_set_desc_avail(struct vring_desc_packed *desc, int wrap_counter)
> +{
> + desc->flags |= VRING_DESC_F_AVAIL(wrap_counter) |
> + VRING_DESC_F_USED(!wrap_counter);
It implies the avail and used bits to be cleared beforehand.
Maybe it would be safer to clear them in the helper?
> +}
> +
> +static inline void
> +set_desc_avail(struct vring *vr, struct vring_desc_packed *desc)
> +{
> + _set_desc_avail(desc, vr->avail_wrap_counter);
> +}
> +
> +static inline int
> +desc_is_used(struct vring_desc_packed *desc, struct vring *vr)
> +{
> + uint16_t used, avail;
> +
> + used = !!(desc->flags & VRING_DESC_F_USED(1));
> + avail = !!(desc->flags & VRING_DESC_F_AVAIL(1));
> +
> + return used == avail && used == vr->used_wrap_counter;
> +}
> +
> /* The standard layout for the ring is a continuous chunk of memory which
> * looks like this. We assume num is a power of 2.
> *
> diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
> index d2a0b651a..53fce61b4 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -245,6 +245,25 @@ struct virtio_tx_region {
> __attribute__((__aligned__(16)));
> };
>
> +static inline uint16_t
> +increment_pq_index(uint16_t idx, size_t ring_size)
> +{
> + return ++idx >= ring_size ? 0 : idx;
> +}
Not sure this helper is really useful, as it ends up
doing two checks in a row.
> +
> +static inline uint16_t
> +update_pq_avail_index(struct virtqueue *vq)
> +{
> + uint16_t idx;
> +
> + idx = increment_pq_index(vq->vq_avail_idx, vq->vq_nentries);
> + if (idx == 0)
> + vq->vq_ring.avail_wrap_counter ^= 1;
> + vq->vq_avail_idx = idx;
> +
> + return vq->vq_avail_idx;
> +}
So it could be simplified to:
{
if (++vq->vq_avail_idx >= vq->vq_entries) {
vq->vq_avail_idx = 0;
vq->vq_ring.avail_wrap_counter ^= 1;
}
return vq->vq_avail_idx;
}
> +
> static inline void
> vring_desc_init_packed(struct vring *vr, int n)
> {
>