On Tue, Dec 27, 2022 at 7:38 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Mon, Dec 26, 2022 at 03:49:07PM +0800, Jason Wang wrote:
> > This patch introduces a per virtqueue waitqueue to allow driver to
> > sleep and wait for more used. Two new helpers are introduced to allow
> > driver to sleep and wake up.
> >
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > ---
> > Changes since V1:
> > - check virtqueue_is_broken() as well
> > - use more_used() instead of virtqueue_get_buf() to allow caller to
> > get buffers afterwards
> > ---
> > drivers/virtio/virtio_ring.c | 29 +++++++++++++++++++++++++++++
> > include/linux/virtio.h | 3 +++
> > 2 files changed, 32 insertions(+)
> >
> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > index 5cfb2fa8abee..9c83eb945493 100644
> > --- a/drivers/virtio/virtio_ring.c
> > +++ b/drivers/virtio/virtio_ring.c
> > @@ -13,6 +13,7 @@
> > #include <linux/dma-mapping.h>
> > #include <linux/kmsan.h>
> > #include <linux/spinlock.h>
> > +#include <linux/wait.h>
> > #include <xen/xen.h>
> >
> > #ifdef DEBUG
> > @@ -60,6 +61,7 @@
> > "%s:"fmt, (_vq)->vq.name, ##args); \
> > /* Pairs with READ_ONCE() in virtqueue_is_broken(). */ \
> > WRITE_ONCE((_vq)->broken, true); \
> > + wake_up_interruptible(&(_vq)->wq); \
> > } while (0)
> > #define START_USE(vq)
> > #define END_USE(vq)
> > @@ -203,6 +205,9 @@ struct vring_virtqueue {
> > /* DMA, allocation, and size information */
> > bool we_own_ring;
> >
> > + /* Wait for buffer to be used */
> > + wait_queue_head_t wq;
> > +
> > #ifdef DEBUG
> > /* They're supposed to lock for us. */
> > unsigned int in_use;
> > @@ -2024,6 +2029,8 @@ static struct virtqueue *vring_create_virtqueue_packed(
> > if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
> > vq->weak_barriers = false;
> >
> > + init_waitqueue_head(&vq->wq);
> > +
> > err = vring_alloc_state_extra_packed(&vring_packed);
> > if (err)
> > goto err_state_extra;
> > @@ -2517,6 +2524,8 @@ static struct virtqueue *__vring_new_virtqueue(unsigned int index,
> > if (virtio_has_feature(vdev, VIRTIO_F_ORDER_PLATFORM))
> > vq->weak_barriers = false;
> >
> > + init_waitqueue_head(&vq->wq);
> > +
> > err = vring_alloc_state_extra_split(vring_split);
> > if (err) {
> > kfree(vq);
> > @@ -2654,6 +2663,8 @@ static void vring_free(struct virtqueue *_vq)
> > {
> > struct vring_virtqueue *vq = to_vvq(_vq);
> >
> > + wake_up_interruptible(&vq->wq);
> > +
> > if (vq->we_own_ring) {
> > if (vq->packed_ring) {
> > vring_free_queue(vq->vq.vdev,
> > @@ -2863,4 +2874,22 @@ const struct vring *virtqueue_get_vring(struct virtqueue *vq)
> > }
> > EXPORT_SYMBOL_GPL(virtqueue_get_vring);
> >
> > +int virtqueue_wait_for_used(struct virtqueue *_vq)
> > +{
> > + struct vring_virtqueue *vq = to_vvq(_vq);
> > +
> > + /* TODO: Tweak the timeout. */
> > + return wait_event_interruptible_timeout(vq->wq,
> > + virtqueue_is_broken(_vq) || more_used(vq), HZ);
>
> BTW undocumented that you also make it interruptible.
> So if we get an interrupt then this will fail.
Yes, this is sub-optimal.
> But device is still going and will later use the buffers.
>
> Same for timeout really.
Avoiding infinite wait/poll is one of the goals, another is to sleep.
If we think the timeout is hard, we can start from the wait.
Thanks
>
>
>
> > +}
> > +EXPORT_SYMBOL_GPL(virtqueue_wait_for_used);
> > +
> > +void virtqueue_wake_up(struct virtqueue *_vq)
> > +{
> > + struct vring_virtqueue *vq = to_vvq(_vq);
> > +
> > + wake_up_interruptible(&vq->wq);
> > +}
> > +EXPORT_SYMBOL_GPL(virtqueue_wake_up);
> > +
> > MODULE_LICENSE("GPL");
> > diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> > index dcab9c7e8784..2eb62c774895 100644
> > --- a/include/linux/virtio.h
> > +++ b/include/linux/virtio.h
> > @@ -72,6 +72,9 @@ void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
> > void *virtqueue_get_buf_ctx(struct virtqueue *vq, unsigned int *len,
> > void **ctx);
> >
> > +int virtqueue_wait_for_used(struct virtqueue *vq);
> > +void virtqueue_wake_up(struct virtqueue *vq);
> > +
> > void virtqueue_disable_cb(struct virtqueue *vq);
> >
> > bool virtqueue_enable_cb(struct virtqueue *vq);
> > --
> > 2.25.1
>
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