Re: [RFC PATCH net-next 2/6] virtio: introduce virtio_enable_cb_avail()
On Wed, Oct 15, 2014 at 06:58:15PM +0800, Jason Wang wrote:
> On 10/15/2014 06:41 PM, Michael S. Tsirkin wrote:
> > On Wed, Oct 15, 2014 at 06:19:15PM +0800, Jason Wang wrote:
> >> On 10/15/2014 05:28 PM, Michael S. Tsirkin wrote:
> >>> On Wed, Oct 15, 2014 at 03:25:26PM +0800, Jason Wang wrote:
> This patch introduces virtio_enable_cb_avail() to publish avail idx
> and used event. This could be used by batched buffer submitting to
> reduce the number of tx interrupts.
>
> Cc: Rusty Russell
> Cc: Michael S. Tsirkin
> Signed-off-by: Jason Wang
> ---
> drivers/virtio/virtio_ring.c | 22 --
> include/linux/virtio.h |2 ++
> 2 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 1b3929f..d67fbf8 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -567,14 +567,32 @@ unsigned virtqueue_enable_cb_prepare(struct
> virtqueue *_vq)
> * entry. Always do both to keep code simple. */
> vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
> /* Make sure used event never go backwards */
> -if (!vring_need_event(vring_used_event(&vq->vring),
> - vq->vring.avail->idx, last_used_idx))
> +if (vq->vring.avail->idx != vring_used_event(&vq->vring) &&
> +!vring_need_event(vring_used_event(&vq->vring),
> + vq->vring.avail->idx, last_used_idx)) {
> vring_used_event(&vq->vring) = last_used_idx;
> +}
> END_USE(vq);
> return last_used_idx;
> }
> EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
>
> >>> I see you are also changing virtqueue_enable_cb_prepare, why?
> >> This is also used to prevent it from moving the used event backwards.
> >> This may happens when we handle tx napi after we publish avail idx as
> >> used event (virtqueue_enable_cb_avail() was called).
> > So it's wrong exactly in the same way.
> >
> > But also, please document this stuff, don't put
> > unrelated changes in a patch called "introduce
> > virtqueue_enable_cb_avail".
> >
> >
> +bool virtqueue_enable_cb_avail(struct virtqueue *_vq)
> +{
> +struct vring_virtqueue *vq = to_vvq(_vq);
> +bool ret;
> +
> +START_USE(vq);
> +vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
> +vring_used_event(&vq->vring) = vq->vring.avail->idx;
> +ret = vring_need_event(vq->vring.avail->idx,
> + vq->last_used_idx, vq->vring.used->idx);
> +END_USE(vq);
> +
> +return ret;
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_avail);
> +
> /**
> * virtqueue_poll - query pending used buffers
> * @vq: the struct virtqueue we're talking about.
> >>> Could not figure out what this does.
> >>> Please add documentation.
> >>>
> >> Sure, does something like below explain what does this function do?
> >>
> >> /**
> >>
> >>
> >> * virtqueue_enable_cb_avail - restart callbacks after
> >> disable_cb.
> >> * @vq: the struct virtqueue we're talking
> >> about.
> >> *
> >>
> >>
> >> * This re-enables callbacks but hints to the other side to
> >> delay
> >> * interrupts all of the available buffers have been processed;
> >
> > So this is like virtqueue_enable_cb_delayed but even more
> > aggressive?
> > I think it's too agressive: it's better to wake up guest
> > after you are through most of buffers, but not all,
> > so guest and host can work in parallel.
>
> Note that:
>
> - it was only used when there are still few of free slots (which is
> greater than 2 + MAX_SKB_FRAGS)
> - my patch keeps the free_old_xmit_skbs() in the beginning of
> start_xmit(), so the tx skb reclaiming does not depends totally on tx
> interrupt. If more packets comes, we'd expect some of them were freed in
> ndo_start_xmit(). If not, finally we may trigger the
> virtqueue_enable_cb_delayed().
>
> So probably not as aggressive as it looks. I will do benchmark on this.
Mine too:
} else if (virtqueue_enable_cb_delayed(sq->vq)) {
free_old_xmit_skbs(txq, sq, qsize);
}
> >
> >
> >> * it returns "false" if there are at least one pending buffer in the
> >> queue,
> >> * to detect a possible race between the driver checking for more
> >> work,
> >> * and enabling
> >> callbacks.
> >> *
Re: [RFC PATCH net-next 2/6] virtio: introduce virtio_enable_cb_avail()
On 10/15/2014 06:41 PM, Michael S. Tsirkin wrote:
> On Wed, Oct 15, 2014 at 06:19:15PM +0800, Jason Wang wrote:
>> On 10/15/2014 05:28 PM, Michael S. Tsirkin wrote:
>>> On Wed, Oct 15, 2014 at 03:25:26PM +0800, Jason Wang wrote:
This patch introduces virtio_enable_cb_avail() to publish avail idx
and used event. This could be used by batched buffer submitting to
reduce the number of tx interrupts.
Cc: Rusty Russell
Cc: Michael S. Tsirkin
Signed-off-by: Jason Wang
---
drivers/virtio/virtio_ring.c | 22 --
include/linux/virtio.h |2 ++
2 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 1b3929f..d67fbf8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -567,14 +567,32 @@ unsigned virtqueue_enable_cb_prepare(struct
virtqueue *_vq)
* entry. Always do both to keep code simple. */
vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
/* Make sure used event never go backwards */
- if (!vring_need_event(vring_used_event(&vq->vring),
-vq->vring.avail->idx, last_used_idx))
+ if (vq->vring.avail->idx != vring_used_event(&vq->vring) &&
+ !vring_need_event(vring_used_event(&vq->vring),
+vq->vring.avail->idx, last_used_idx)) {
vring_used_event(&vq->vring) = last_used_idx;
+ }
END_USE(vq);
return last_used_idx;
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
>>> I see you are also changing virtqueue_enable_cb_prepare, why?
>> This is also used to prevent it from moving the used event backwards.
>> This may happens when we handle tx napi after we publish avail idx as
>> used event (virtqueue_enable_cb_avail() was called).
> So it's wrong exactly in the same way.
>
> But also, please document this stuff, don't put
> unrelated changes in a patch called "introduce
> virtqueue_enable_cb_avail".
>
>
+bool virtqueue_enable_cb_avail(struct virtqueue *_vq)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+ bool ret;
+
+ START_USE(vq);
+ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
+ vring_used_event(&vq->vring) = vq->vring.avail->idx;
+ ret = vring_need_event(vq->vring.avail->idx,
+ vq->last_used_idx, vq->vring.used->idx);
+ END_USE(vq);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(virtqueue_enable_cb_avail);
+
/**
* virtqueue_poll - query pending used buffers
* @vq: the struct virtqueue we're talking about.
>>> Could not figure out what this does.
>>> Please add documentation.
>>>
>> Sure, does something like below explain what does this function do?
>>
>> /**
>>
>>
>> * virtqueue_enable_cb_avail - restart callbacks after
>> disable_cb.
>> * @vq: the struct virtqueue we're talking
>> about.
>> *
>>
>>
>> * This re-enables callbacks but hints to the other side to
>> delay
>> * interrupts all of the available buffers have been processed;
>
> So this is like virtqueue_enable_cb_delayed but even more
> aggressive?
> I think it's too agressive: it's better to wake up guest
> after you are through most of buffers, but not all,
> so guest and host can work in parallel.
Note that:
- it was only used when there are still few of free slots (which is
greater than 2 + MAX_SKB_FRAGS)
- my patch keeps the free_old_xmit_skbs() in the beginning of
start_xmit(), so the tx skb reclaiming does not depends totally on tx
interrupt. If more packets comes, we'd expect some of them were freed in
ndo_start_xmit(). If not, finally we may trigger the
virtqueue_enable_cb_delayed().
So probably not as aggressive as it looks. I will do benchmark on this.
>
>
>> * it returns "false" if there are at least one pending buffer in the
>> queue,
>> * to detect a possible race between the driver checking for more
>> work,
>> * and enabling
>> callbacks.
>> *
>>
>>
>> * Caller must ensure we don't call this with other
>> virtqueue
>> * operations at the same time (except where
>> noted).
>> */
>>
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index b46671e..bfaf058 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -65,6 +65,8 @@ bool virtqueue_enable_cb(struct virtqueue *vq);
unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
+bool virtqu
Re: [RFC PATCH net-next 2/6] virtio: introduce virtio_enable_cb_avail()
On Wed, Oct 15, 2014 at 06:19:15PM +0800, Jason Wang wrote:
> On 10/15/2014 05:28 PM, Michael S. Tsirkin wrote:
> > On Wed, Oct 15, 2014 at 03:25:26PM +0800, Jason Wang wrote:
> >> This patch introduces virtio_enable_cb_avail() to publish avail idx
> >> and used event. This could be used by batched buffer submitting to
> >> reduce the number of tx interrupts.
> >>
> >> Cc: Rusty Russell
> >> Cc: Michael S. Tsirkin
> >> Signed-off-by: Jason Wang
> >> ---
> >> drivers/virtio/virtio_ring.c | 22 --
> >> include/linux/virtio.h |2 ++
> >> 2 files changed, 22 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> >> index 1b3929f..d67fbf8 100644
> >> --- a/drivers/virtio/virtio_ring.c
> >> +++ b/drivers/virtio/virtio_ring.c
> >> @@ -567,14 +567,32 @@ unsigned virtqueue_enable_cb_prepare(struct
> >> virtqueue *_vq)
> >> * entry. Always do both to keep code simple. */
> >>vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
> >>/* Make sure used event never go backwards */
> >> - if (!vring_need_event(vring_used_event(&vq->vring),
> >> -vq->vring.avail->idx, last_used_idx))
> >> + if (vq->vring.avail->idx != vring_used_event(&vq->vring) &&
> >> + !vring_need_event(vring_used_event(&vq->vring),
> >> +vq->vring.avail->idx, last_used_idx)) {
> >>vring_used_event(&vq->vring) = last_used_idx;
> >> + }
> >>END_USE(vq);
> >>return last_used_idx;
> >> }
> >> EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
> >>
> > I see you are also changing virtqueue_enable_cb_prepare, why?
>
> This is also used to prevent it from moving the used event backwards.
> This may happens when we handle tx napi after we publish avail idx as
> used event (virtqueue_enable_cb_avail() was called).
So it's wrong exactly in the same way.
But also, please document this stuff, don't put
unrelated changes in a patch called "introduce
virtqueue_enable_cb_avail".
> >
> >> +bool virtqueue_enable_cb_avail(struct virtqueue *_vq)
> >> +{
> >> + struct vring_virtqueue *vq = to_vvq(_vq);
> >> + bool ret;
> >> +
> >> + START_USE(vq);
> >> + vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
> >> + vring_used_event(&vq->vring) = vq->vring.avail->idx;
> >> + ret = vring_need_event(vq->vring.avail->idx,
> >> + vq->last_used_idx, vq->vring.used->idx);
> >> + END_USE(vq);
> >> +
> >> + return ret;
> >> +}
> >> +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_avail);
> >> +
> >> /**
> >> * virtqueue_poll - query pending used buffers
> >> * @vq: the struct virtqueue we're talking about.
> > Could not figure out what this does.
> > Please add documentation.
> >
>
> Sure, does something like below explain what does this function do?
>
> /**
>
>
> * virtqueue_enable_cb_avail - restart callbacks after
> disable_cb.
> * @vq: the struct virtqueue we're talking
> about.
> *
>
>
> * This re-enables callbacks but hints to the other side to
> delay
> * interrupts all of the available buffers have been processed;
So this is like virtqueue_enable_cb_delayed but even more
aggressive?
I think it's too agressive: it's better to wake up guest
after you are through most of buffers, but not all,
so guest and host can work in parallel.
> * it returns "false" if there are at least one pending buffer in the
> queue,
> * to detect a possible race between the driver checking for more
> work,
> * and enabling
> callbacks.
> *
>
>
> * Caller must ensure we don't call this with other
> virtqueue
> * operations at the same time (except where
> noted).
> */
>
> >> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> >> index b46671e..bfaf058 100644
> >> --- a/include/linux/virtio.h
> >> +++ b/include/linux/virtio.h
> >> @@ -65,6 +65,8 @@ bool virtqueue_enable_cb(struct virtqueue *vq);
> >>
> >> unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
> >>
> >> +bool virtqueue_enable_cb_avail(struct virtqueue *vq);
> >> +
> >> bool virtqueue_poll(struct virtqueue *vq, unsigned);
> >>
> >> bool virtqueue_enable_cb_delayed(struct virtqueue *vq);
> >> --
> >> 1.7.1
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majord...@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at http://www.tux.org/lkml/
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Re: [RFC PATCH net-next 2/6] virtio: introduce virtio_enable_cb_avail()
On 10/15/2014 05:28 PM, Michael S. Tsirkin wrote:
> On Wed, Oct 15, 2014 at 03:25:26PM +0800, Jason Wang wrote:
>> This patch introduces virtio_enable_cb_avail() to publish avail idx
>> and used event. This could be used by batched buffer submitting to
>> reduce the number of tx interrupts.
>>
>> Cc: Rusty Russell
>> Cc: Michael S. Tsirkin
>> Signed-off-by: Jason Wang
>> ---
>> drivers/virtio/virtio_ring.c | 22 --
>> include/linux/virtio.h |2 ++
>> 2 files changed, 22 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
>> index 1b3929f..d67fbf8 100644
>> --- a/drivers/virtio/virtio_ring.c
>> +++ b/drivers/virtio/virtio_ring.c
>> @@ -567,14 +567,32 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue
>> *_vq)
>> * entry. Always do both to keep code simple. */
>> vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
>> /* Make sure used event never go backwards */
>> -if (!vring_need_event(vring_used_event(&vq->vring),
>> - vq->vring.avail->idx, last_used_idx))
>> +if (vq->vring.avail->idx != vring_used_event(&vq->vring) &&
>> +!vring_need_event(vring_used_event(&vq->vring),
>> + vq->vring.avail->idx, last_used_idx)) {
>> vring_used_event(&vq->vring) = last_used_idx;
>> +}
>> END_USE(vq);
>> return last_used_idx;
>> }
>> EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
>>
> I see you are also changing virtqueue_enable_cb_prepare, why?
This is also used to prevent it from moving the used event backwards.
This may happens when we handle tx napi after we publish avail idx as
used event (virtqueue_enable_cb_avail() was called).
>
>> +bool virtqueue_enable_cb_avail(struct virtqueue *_vq)
>> +{
>> +struct vring_virtqueue *vq = to_vvq(_vq);
>> +bool ret;
>> +
>> +START_USE(vq);
>> +vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
>> +vring_used_event(&vq->vring) = vq->vring.avail->idx;
>> +ret = vring_need_event(vq->vring.avail->idx,
>> + vq->last_used_idx, vq->vring.used->idx);
>> +END_USE(vq);
>> +
>> +return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_avail);
>> +
>> /**
>> * virtqueue_poll - query pending used buffers
>> * @vq: the struct virtqueue we're talking about.
> Could not figure out what this does.
> Please add documentation.
>
Sure, does something like below explain what does this function do?
/**
* virtqueue_enable_cb_avail - restart callbacks after
disable_cb.
* @vq: the struct virtqueue we're talking
about.
*
* This re-enables callbacks but hints to the other side to
delay
* interrupts all of the available buffers have been processed;
* it returns "false" if there are at least one pending buffer in the
queue,
* to detect a possible race between the driver checking for more
work,
* and enabling
callbacks.
*
* Caller must ensure we don't call this with other
virtqueue
* operations at the same time (except where
noted).
*/
>> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
>> index b46671e..bfaf058 100644
>> --- a/include/linux/virtio.h
>> +++ b/include/linux/virtio.h
>> @@ -65,6 +65,8 @@ bool virtqueue_enable_cb(struct virtqueue *vq);
>>
>> unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
>>
>> +bool virtqueue_enable_cb_avail(struct virtqueue *vq);
>> +
>> bool virtqueue_poll(struct virtqueue *vq, unsigned);
>>
>> bool virtqueue_enable_cb_delayed(struct virtqueue *vq);
>> --
>> 1.7.1
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
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Re: [RFC PATCH net-next 2/6] virtio: introduce virtio_enable_cb_avail()
On Wed, Oct 15, 2014 at 03:25:26PM +0800, Jason Wang wrote:
> This patch introduces virtio_enable_cb_avail() to publish avail idx
> and used event. This could be used by batched buffer submitting to
> reduce the number of tx interrupts.
>
> Cc: Rusty Russell
> Cc: Michael S. Tsirkin
> Signed-off-by: Jason Wang
> ---
> drivers/virtio/virtio_ring.c | 22 --
> include/linux/virtio.h |2 ++
> 2 files changed, 22 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 1b3929f..d67fbf8 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -567,14 +567,32 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue
> *_vq)
>* entry. Always do both to keep code simple. */
> vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
> /* Make sure used event never go backwards */
> - if (!vring_need_event(vring_used_event(&vq->vring),
> - vq->vring.avail->idx, last_used_idx))
> + if (vq->vring.avail->idx != vring_used_event(&vq->vring) &&
> + !vring_need_event(vring_used_event(&vq->vring),
> + vq->vring.avail->idx, last_used_idx)) {
> vring_used_event(&vq->vring) = last_used_idx;
> + }
> END_USE(vq);
> return last_used_idx;
> }
> EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
>
I see you are also changing virtqueue_enable_cb_prepare, why?
> +bool virtqueue_enable_cb_avail(struct virtqueue *_vq)
> +{
> + struct vring_virtqueue *vq = to_vvq(_vq);
> + bool ret;
> +
> + START_USE(vq);
> + vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
> + vring_used_event(&vq->vring) = vq->vring.avail->idx;
> + ret = vring_need_event(vq->vring.avail->idx,
> +vq->last_used_idx, vq->vring.used->idx);
> + END_USE(vq);
> +
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_avail);
> +
> /**
> * virtqueue_poll - query pending used buffers
> * @vq: the struct virtqueue we're talking about.
Could not figure out what this does.
Please add documentation.
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index b46671e..bfaf058 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -65,6 +65,8 @@ bool virtqueue_enable_cb(struct virtqueue *vq);
>
> unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
>
> +bool virtqueue_enable_cb_avail(struct virtqueue *vq);
> +
> bool virtqueue_poll(struct virtqueue *vq, unsigned);
>
> bool virtqueue_enable_cb_delayed(struct virtqueue *vq);
> --
> 1.7.1
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[RFC PATCH net-next 2/6] virtio: introduce virtio_enable_cb_avail()
This patch introduces virtio_enable_cb_avail() to publish avail idx
and used event. This could be used by batched buffer submitting to
reduce the number of tx interrupts.
Cc: Rusty Russell
Cc: Michael S. Tsirkin
Signed-off-by: Jason Wang
---
drivers/virtio/virtio_ring.c | 22 --
include/linux/virtio.h |2 ++
2 files changed, 22 insertions(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 1b3929f..d67fbf8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -567,14 +567,32 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue
*_vq)
* entry. Always do both to keep code simple. */
vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
/* Make sure used event never go backwards */
- if (!vring_need_event(vring_used_event(&vq->vring),
- vq->vring.avail->idx, last_used_idx))
+ if (vq->vring.avail->idx != vring_used_event(&vq->vring) &&
+ !vring_need_event(vring_used_event(&vq->vring),
+ vq->vring.avail->idx, last_used_idx)) {
vring_used_event(&vq->vring) = last_used_idx;
+ }
END_USE(vq);
return last_used_idx;
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
+bool virtqueue_enable_cb_avail(struct virtqueue *_vq)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+ bool ret;
+
+ START_USE(vq);
+ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
+ vring_used_event(&vq->vring) = vq->vring.avail->idx;
+ ret = vring_need_event(vq->vring.avail->idx,
+ vq->last_used_idx, vq->vring.used->idx);
+ END_USE(vq);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(virtqueue_enable_cb_avail);
+
/**
* virtqueue_poll - query pending used buffers
* @vq: the struct virtqueue we're talking about.
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index b46671e..bfaf058 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -65,6 +65,8 @@ bool virtqueue_enable_cb(struct virtqueue *vq);
unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
+bool virtqueue_enable_cb_avail(struct virtqueue *vq);
+
bool virtqueue_poll(struct virtqueue *vq, unsigned);
bool virtqueue_enable_cb_delayed(struct virtqueue *vq);
--
1.7.1
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