[PATCH RFC v5 net-next 1/6] virtio_ring: fix virtqueue_enable_cb() when only 1 buffers were pending
From: Jason Wang <jasowang@redhat.com>
Date: 2015-02-09 08:39:57
Also in:
lkml, netdev
Subsystem:
the rest, virtio core · Maintainers:
Linus Torvalds, "Michael S. Tsirkin", Jason Wang
We currently does: bufs = (avail->idx - last_used_idx) * 3 / 4; This is ok now since we only try to enable the delayed callbacks when the queue is about to be full. This may not work well when there is only one pending buffer in the virtqueue (this may be the case after tx interrupt was enabled). Since virtqueue_enable_cb() will return false which may cause unnecessary triggering of napis. This patch correct this by only calculate the four thirds when bufs is not one. Signed-off-by: Jason Wang <jasowang@redhat.com> --- drivers/virtio/virtio_ring.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 00ec6b3..545fed5 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c@@ -636,7 +636,10 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq) * entry. Always do both to keep code simple. */ vq->vring.avail->flags &= cpu_to_virtio16(_vq->vdev, ~VRING_AVAIL_F_NO_INTERRUPT); /* TODO: tune this threshold */ - bufs = (u16)(virtio16_to_cpu(_vq->vdev, vq->vring.avail->idx) - vq->last_used_idx) * 3 / 4; + bufs = (u16)(virtio16_to_cpu(_vq->vdev, vq->vring.avail->idx) - + vq->last_used_idx); + if (bufs != 1) + bufs = bufs * 3 / 4; vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs); virtio_mb(vq->weak_barriers); if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) - vq->last_used_idx) > bufs)) {
--
1.8.3.1