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To: Jens Freimann <jfreimann@redhat.com>, dev@dpdk.org
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<20181214155916.1142-3-jfreimann@redhat.com>
From: Maxime Coquelin <maxime.coquelin@redhat.com>
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(mx1.redhat.com [10.5.110.27]); Mon, 17 Dec 2018 16:10:03 +0000 (UTC)
Subject: Re: [dpdk-dev] [PATCH v13 02/10] net/virtio: add packed virtqueue
helpers
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On 12/14/18 4:59 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_pci.h | 6 +++
> drivers/net/virtio/virtqueue.h | 91 ++++++++++++++++++++++++++++++++-
> 2 files changed, 95 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_pci.h b/drivers/net/virtio/virtio_pci.h
> index 4c975a531..b22b62dad 100644
> --- a/drivers/net/virtio/virtio_pci.h
> +++ b/drivers/net/virtio/virtio_pci.h
> @@ -315,6 +315,12 @@ 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/virtqueue.h b/drivers/net/virtio/virtqueue.h
> index d4e0858e4..19fabae0b 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -251,6 +251,44 @@ struct virtio_tx_region {
> __attribute__((__aligned__(16)));
> };
>
> +static inline void
> +_set_desc_avail(struct vring_packed_desc *desc, int wrap_counter)
> +{
> + desc->flags |= VRING_DESC_F_AVAIL(wrap_counter) |
> + VRING_DESC_F_USED(!wrap_counter);
> +}
> +
> +static inline void
> +set_desc_avail(struct virtqueue *vq, struct vring_packed_desc *desc)
> +{
> + _set_desc_avail(desc, vq->avail_wrap_counter);
> +}
> +
> +static inline int
> +desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq)
> +{
> + uint16_t used, avail, flags;
> +
> + flags = desc->flags;
> + used = !!(flags & VRING_DESC_F_USED(1));
> + avail = !!(flags & VRING_DESC_F_AVAIL(1));
> +
> + return avail == used && used == vq->used_wrap_counter;
> +}
> +
> +
> +static inline void
> +vring_desc_init_packed(struct virtqueue *vq, int n)
> +{
> + int i;
> + for (i = 0; i < n - 1; i++) {
> + vq->ring_packed.desc_packed[i].id = i;
> + vq->vq_descx[i].next = i + 1;
> + }
> + vq->ring_packed.desc_packed[i].id = i;
> + vq->vq_descx[i].next = VQ_RING_DESC_CHAIN_END;
> +}
> +
> /* Chain all the descriptors in the ring with an END */
> static inline void
> vring_desc_init(struct vring_desc *dp, uint16_t n)
> @@ -262,13 +300,59 @@ vring_desc_init(struct vring_desc *dp, uint16_t n)
> dp[i].next = VQ_RING_DESC_CHAIN_END;
> }
>
> +/**
> + * Tell the backend not to interrupt us.
> + */
> +static inline void
> +virtqueue_disable_intr_packed(struct virtqueue *vq)
> +{
> + uint16_t *event_flags = &vq->ring_packed.driver_event->desc_event_flags;
> +
> + if (*event_flags != RING_EVENT_FLAGS_DISABLE)
> + *event_flags = RING_EVENT_FLAGS_DISABLE;
Why not just setting the value unconditionally?
IIUC, it is not called in the hot path?
> +}
> +
> +
> /**
> * Tell the backend not to interrupt us.
> */
> static inline void
> virtqueue_disable_intr(struct virtqueue *vq)
> {
> - vq->vq_ring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
> + if (vtpci_packed_queue(vq->hw))
> + virtqueue_disable_intr_packed(vq);
> + else
> + vq->vq_ring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
> +}
> +
> +/**
> + * Tell the backend to interrupt. Implementation for packed virtqueues.
> + */
> +static inline void
> +virtqueue_enable_intr_packed(struct virtqueue *vq)
> +{
> + uint16_t *off_wrap = &vq->ring_packed.driver_event->desc_event_off_wrap;
> + uint16_t *event_flags = &vq->ring_packed.driver_event->desc_event_flags;
> +
> + *off_wrap = vq->vq_used_cons_idx |
> + ((uint16_t)(vq->used_wrap_counter << 15));
Don't we want to set off_wrap only if VIRTIO_RING_F_EVENT_IDX
negotiated?
> +
> + if (vq->event_flags_shadow == RING_EVENT_FLAGS_DISABLE) {
> + virtio_wmb();
> + vq->event_flags_shadow =
> + vtpci_with_feature(vq->hw, VIRTIO_RING_F_EVENT_IDX) ?
> + RING_EVENT_FLAGS_DESC : RING_EVENT_FLAGS_ENABLE;
> + *event_flags = vq->event_flags_shadow;
> + }
> +}
> +
> +/**
> + * Tell the backend to interrupt. Implementation for split virtqueues.
> + */
> +static inline void
> +virtqueue_enable_intr_split(struct virtqueue *vq)
> +{
> + vq->vq_ring.avail->flags &= (~VRING_AVAIL_F_NO_INTERRUPT);
> }
>
> /**
> @@ -277,7 +361,10 @@ virtqueue_disable_intr(struct virtqueue *vq)
> static inline void
> virtqueue_enable_intr(struct virtqueue *vq)
> {
> - vq->vq_ring.avail->flags &= (~VRING_AVAIL_F_NO_INTERRUPT);
> + if (vtpci_packed_queue(vq->hw))
> + virtqueue_enable_intr_packed(vq);
> + else
> + virtqueue_enable_intr_split(vq);
> }
>
> /**
>