On Mon, Feb 09, 2015 at 03:39:21AM -0500, Jason Wang wrote: > Currently, we do nothing to prevent the callbacks in > virtqueue_disable_cb() when event index is used. This may cause > spurious interrupts which may damage the performance. This patch tries > to publish avail event as the used even to prevent the callbacks. > > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> I'm surprised that this ever happens though. Normally we call this after getting an interrupt, and interrupts won't trigger again until the rings wraps around. When I tested this, touching an extra cache line was more expensive. Does this really reduce number of interrupts? Could you pls share some numbers with and without this patch? > --- > drivers/virtio/virtio_ring.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 545fed5..e9ffbfb 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -539,6 +539,8 @@ void virtqueue_disable_cb(struct virtqueue *_vq) > struct vring_virtqueue *vq = to_vvq(_vq); > > vq->vring.avail->flags |= cpu_to_virtio16(_vq->vdev, VRING_AVAIL_F_NO_INTERRUPT); > + vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, > + vq->vring.avail->idx); Hmm in fact, can't this actually cause an extra interrupt when avail->idx is completed? I think that if you really can show disabling interrupts like this helps, you should set some invalid value like 0xfffff, or move it back to vq->vring.avail->idx - 1. No? > } > EXPORT_SYMBOL_GPL(virtqueue_disable_cb); > > -- > 1.8.3.1 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
