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author | Michael S. Tsirkin <mst@redhat.com> | 2013-07-09 13:19:18 +0300 |
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committer | David S. Miller <davem@davemloft.net> | 2013-07-09 12:45:37 -0700 |
commit | cc229884d3f77ec3b1240e467e0236c3e0647c0c (patch) | |
tree | a2617adb191288d049629f911b7fef7038557a8e /drivers/virtio/virtio_ring.c | |
parent | 01276ed2424eb78c95461545410923d5da154d31 (diff) | |
download | op-kernel-dev-cc229884d3f77ec3b1240e467e0236c3e0647c0c.zip op-kernel-dev-cc229884d3f77ec3b1240e467e0236c3e0647c0c.tar.gz |
virtio: support unlocked queue poll
This adds a way to check ring empty state after enable_cb outside any
locks. Will be used by virtio_net.
Note: there's room for more optimization: caller is likely to have a
memory barrier already, which means we might be able to get rid of a
barrier here. Deferring this optimization until we do some
benchmarking.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers/virtio/virtio_ring.c')
-rw-r--r-- | drivers/virtio/virtio_ring.c | 56 |
1 files changed, 44 insertions, 12 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 5217baf5..37d58f8 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -607,19 +607,21 @@ void virtqueue_disable_cb(struct virtqueue *_vq) EXPORT_SYMBOL_GPL(virtqueue_disable_cb); /** - * virtqueue_enable_cb - restart callbacks after disable_cb. + * virtqueue_enable_cb_prepare - restart callbacks after disable_cb * @vq: the struct virtqueue we're talking about. * - * 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. + * This re-enables callbacks; it returns current queue state + * in an opaque unsigned value. This value should be later tested by + * virtqueue_poll, to detect a possible race between the driver checking for + * more work, and enabling callbacks. * * Caller must ensure we don't call this with other virtqueue * operations at the same time (except where noted). */ -bool virtqueue_enable_cb(struct virtqueue *_vq) +unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); + u16 last_used_idx; START_USE(vq); @@ -629,15 +631,45 @@ bool virtqueue_enable_cb(struct virtqueue *_vq) * 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; - vring_used_event(&vq->vring) = vq->last_used_idx; + vring_used_event(&vq->vring) = last_used_idx = vq->last_used_idx; + END_USE(vq); + return last_used_idx; +} +EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare); + +/** + * virtqueue_poll - query pending used buffers + * @vq: the struct virtqueue we're talking about. + * @last_used_idx: virtqueue state (from call to virtqueue_enable_cb_prepare). + * + * Returns "true" if there are pending used buffers in the queue. + * + * This does not need to be serialized. + */ +bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx) +{ + struct vring_virtqueue *vq = to_vvq(_vq); + virtio_mb(vq->weak_barriers); - if (unlikely(more_used(vq))) { - END_USE(vq); - return false; - } + return (u16)last_used_idx != vq->vring.used->idx; +} +EXPORT_SYMBOL_GPL(virtqueue_poll); - END_USE(vq); - return true; +/** + * virtqueue_enable_cb - restart callbacks after disable_cb. + * @vq: the struct virtqueue we're talking about. + * + * 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. + * + * Caller must ensure we don't call this with other virtqueue + * operations at the same time (except where noted). + */ +bool virtqueue_enable_cb(struct virtqueue *_vq) +{ + unsigned last_used_idx = virtqueue_enable_cb_prepare(_vq); + return !virtqueue_poll(_vq, last_used_idx); } EXPORT_SYMBOL_GPL(virtqueue_enable_cb); |