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Subject[PATCH 14/18] virtio: add api for delayed callbacks
Add an API that tells the other side that callbacks
should be delayed until a lot of work has been done.
Implement using the new used_event feature.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/virtio/virtio_ring.c | 27 +++++++++++++++++++++++++++
include/linux/virtio.h | 9 +++++++++
2 files changed, 36 insertions(+), 0 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 262dfe6..3a70d70 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -397,6 +397,33 @@ bool virtqueue_enable_cb(struct virtqueue *_vq)
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb);

+bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
+{
+ struct vring_virtqueue *vq = to_vvq(_vq);
+ int bufs;
+
+ START_USE(vq);
+
+ /* We optimistically turn back on interrupts, then check if there was
+ * more to do. */
+ /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
+ * either clear the flags bit or point the event index at the next
+ * entry. Always do both to keep code simple. */
+ vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
+ /* TODO: tune this threshold */
+ bufs = (vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
+ vring_used_event(&vq->vring) = vq->last_used_idx + bufs;
+ virtio_mb();
+ if (unlikely(vq->vring.used->idx - vq->last_used_idx > bufs)) {
+ END_USE(vq);
+ return false;
+ }
+
+ END_USE(vq);
+ return true;
+}
+EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
+
void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 718336b..5151fd1 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -51,6 +51,13 @@ struct virtqueue {
* This re-enables callbacks; it returns "false" if there are pending
* buffers in the queue, to detect a possible race between the driver
* checking for more work, and enabling callbacks.
+ * virtqueue_enable_cb_delayed: 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 until most of the available buffers have been processed;
+ * it returns "false" if there are many pending buffers in the queue,
+ * to detect a possible race between the driver checking for more work,
+ * and enabling callbacks.
* virtqueue_detach_unused_buf: detach first unused buffer
* vq: the struct virtqueue we're talking about.
* Returns NULL or the "data" token handed to add_buf
@@ -86,6 +93,8 @@ void virtqueue_disable_cb(struct virtqueue *vq);

bool virtqueue_enable_cb(struct virtqueue *vq);

+bool virtqueue_enable_cb_delayed(struct virtqueue *vq);
+
void *virtqueue_detach_unused_buf(struct virtqueue *vq);

/**
--
1.7.5.53.gc233e


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