Re: [PATCH v6] vhost: support virtqueue interrupt/notification suppression

[Yuanhan Liu <yliu@fridaylinux.org>]

On Tue, Dec 26, 2017 at 12:43:10PM -0500, Junjie Chen wrote:
> 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@intel.com>

You need put "---" before the change log. Otherwise, it will be tracked in
the commit log.

> +#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)

It's a bit weird that you use one from the standard linux header file
(vring_need_event), while you define you own one (vhost_used_event).
Note that the system header file also has "vring_used_event()" defined.

Besides that, I have few more comments (and some requirements):

- It'd be much better if there is a Tested-by tag. Expeclitly,
  I'm asking a test with Linux kernel virtio-net driver in guest.

- I also hope you could have done a build test on some old distributions.
  AFAIK, the two macros (vring_need_event and vring_used_event) come
  from kernel 3.0 (or above). Any kernel older than that would fail
  the build.

- I'd be great if you could make a new one based on top of my latest
  tree: I have just applied a patchset that should conflict with this
  one.

	--yliu