From 7ab358c23cbf15cea08129cd722d1ce77433a94d Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Fri, 20 May 2011 02:11:14 +0300 Subject: 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 event_idx feature. Note: it might seem advantageous to let the drivers ask for a callback after a specific capacity has been reached. However, as a single head can free many entries in the descriptor table, we don't really have a clue about capacity until get_buf is called. The API is the simplest to implement at the moment, we'll see what kind of hints drivers can pass when there's more than one user of the feature. Signed-off-by: Michael S. Tsirkin Signed-off-by: Rusty Russell --- drivers/virtio/virtio_ring.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) (limited to 'drivers/virtio') diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index a5fadc4..68b9136 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -376,6 +376,33 @@ 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); + u16 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 = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4; + vring_used_event(&vq->vring) = vq->last_used_idx + bufs; + virtio_mb(); + if (unlikely((u16)(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); -- cgit v1.1