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 <rusty@xxxxxxxxxxxxxxx>
>> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
>> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
>> ---
>> 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
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