[dpdk-dev] [PATCH v6] vhost: support virtqueue interrupt/notification suppression

Wang, Xiao W xiao.w.wang at intel.com
Fri Jan 5 06:25:24 CET 2018


Hi,

> -----Original Message-----
> From: Chen, Junjie J
> Sent: Wednesday, December 27, 2017 1:43 AM
> To: Wang, Xiao W <xiao.w.wang at intel.com>; yliu at fridaylinux.org;
> maxime.coquelin at redhat.com; Bie, Tiwei <tiwei.bie at intel.com>
> Cc: dev at dpdk.org; Chen, Junjie J <junjie.j.chen at intel.com>
> Subject: [PATCH v6] vhost: support virtqueue interrupt/notification
> suppression
> 
> The driver can suppress interrupt when VIRTIO_F_EVENT_IDX feature bit is
> negotiated. The driver set vring flags to 0, and MAY use used_event in
> available ring to advise device interrupt util reach an index specified
> by used_event. The device ignore the lower bit of vring flags, and send
> an interrupt when index reach used_event.
> 
> The device can suppress notification in a manner analogous to the ways
> driver suppress interrupt. The device manipulates flags or avail_event in
> the used ring in the same way the driver manipulates flags or used_event in
> available ring.
> 
> This patch is to enable this feature in vhost.
> 
> Signed-off-by: Junjie Chen <junjie.j.chen at intel.com>
> 
> v6:
> Use volatile qualifier to access avail event idx.
> 
> v5:
> Remove updating avail event index in backend.
> 
> v2-v4:
> Use definition of VIRTIO_F_EVENT_IDX from kernel.
> 
> ---
>  lib/librte_vhost/vhost.h      |  3 +++
>  lib/librte_vhost/virtio_net.c | 46 +++++++++++++++++++++++++++++-------------
> -
>  2 files changed, 34 insertions(+), 15 deletions(-)
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 1cc81c1..fc41c20 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -103,6 +103,8 @@ struct vhost_virtqueue {
> 
>  	uint16_t		last_avail_idx;
>  	uint16_t		last_used_idx;
> +	/* Last used index we notify to front end. */
> +	uint16_t		signalled_used;
>  #define VIRTIO_INVALID_EVENTFD		(-1)
>  #define VIRTIO_UNINITIALIZED_EVENTFD	(-2)
> 
> @@ -211,6 +213,7 @@ struct vhost_msg {
>  				(1ULL << VIRTIO_NET_F_GUEST_TSO4) | \
>  				(1ULL << VIRTIO_NET_F_GUEST_TSO6) | \
>  				(1ULL << VIRTIO_RING_F_INDIRECT_DESC) | \
> +				(1ULL << VIRTIO_RING_F_EVENT_IDX) | \
>  				(1ULL << VIRTIO_NET_F_MTU) | \
>  				(1ULL << VIRTIO_F_IOMMU_PLATFORM))
> 
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index 6fee16e..f5777fc 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -52,6 +52,34 @@
> 
>  #define MAX_BATCH_LEN 256
> 
> +#define vhost_used_event(vr) \
> +	(*(volatile uint16_t*)&(vr)->avail->ring[(vr)->size])
> +
> +static __rte_always_inline void
> +vhost_notify(struct virtio_net *dev,  struct vhost_virtqueue *vq)
> +{
> +	/* Don't notify guest if we don't reach index specified by guest. */
> +	if (dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX)) {
> +		uint16_t old = vq->signalled_used;
> +		uint16_t new = vq->last_used_idx;
> +
> +		LOG_DEBUG(VHOST_DATA, "%s: used_event_idx=%d, old=%d,
> new=%d\n",
> +			__func__,
> +			vhost_used_event(vq),
> +			old, new);
> +		if (vring_need_event(vhost_used_event(vq), new, old)
> +			&& (vq->callfd >= 0)) {
> +			vq->signalled_used = vq->last_used_idx;
> +			eventfd_write(vq->callfd, (eventfd_t) 1);
> +		}
> +	} else {
> +		/* Kick the guest if necessary. */
> +		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> +			&& (vq->callfd >= 0))
> +			eventfd_write(vq->callfd, (eventfd_t)1);
> +	}
> +}
> +
>  static bool
>  is_valid_virt_queue_idx(uint32_t idx, int is_tx, uint32_t nr_vring)
>  {
> @@ -410,11 +438,7 @@ virtio_dev_rx(struct virtio_net *dev, uint16_t
> queue_id,
> 
>  	/* flush used->idx update before we read avail->flags. */
>  	rte_mb();
> -
> -	/* Kick the guest if necessary. */
> -	if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> -			&& (vq->callfd >= 0))
> -		eventfd_write(vq->callfd, (eventfd_t)1);
> +	vhost_notify(dev, vq);
>  out:
>  	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
>  		vhost_user_iotlb_rd_unlock(vq);
> @@ -704,11 +728,7 @@ virtio_dev_merge_rx(struct virtio_net *dev, uint16_t
> queue_id,
> 
>  		/* flush used->idx update before we read avail->flags. */
>  		rte_mb();
> -
> -		/* Kick the guest if necessary. */
> -		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> -				&& (vq->callfd >= 0))
> -			eventfd_write(vq->callfd, (eventfd_t)1);
> +		vhost_notify(dev, vq);
>  	}
> 
>  out:
> @@ -1106,11 +1126,7 @@ update_used_idx(struct virtio_net *dev, struct
> vhost_virtqueue *vq,
>  	vq->used->idx += count;
>  	vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
>  			sizeof(vq->used->idx));
> -
> -	/* Kick guest if required. */
> -	if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> -			&& (vq->callfd >= 0))
> -		eventfd_write(vq->callfd, (eventfd_t)1);
> +	vhost_notify(dev, vq);
>  }
> 
>  static __rte_always_inline struct zcopy_mbuf *
> --
> 2.0.1

Reviewed-by: Xiao Wang <xiao.w.wang at intel.com>


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