3.2.50-rc1 review patch. If anyone has any objections, please let me know.
------------------ From: Michael S. Tsirkin <[email protected]> commit cc229884d3f77ec3b1240e467e0236c3e0647c0c upstream. 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 <[email protected]> Signed-off-by: David S. Miller <[email protected]> [wg: Backported to 3.2] Signed-off-by: Wolfram Gloger <[email protected]> Signed-off-by: Ben Hutchings <[email protected]> --- diff -upr linux-3.2.49/drivers/virtio/virtio_ring.c linux-3.2.49wg/drivers/virtio/virtio_ring.c --- linux-3.2.49/drivers/virtio/virtio_ring.c 2013-07-27 18:13:40.000000000 +0200 +++ linux-3.2.49wg/drivers/virtio/virtio_ring.c 2013-07-27 13:57:28.000000000 +0200 @@ -360,9 +360,22 @@ void virtqueue_disable_cb(struct virtque } EXPORT_SYMBOL_GPL(virtqueue_disable_cb); -bool virtqueue_enable_cb(struct virtqueue *_vq) +/** + * virtqueue_enable_cb_prepare - restart callbacks after disable_cb + * @vq: the struct virtqueue we're talking about. + * + * 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). + */ +unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq) { struct vring_virtqueue *vq = to_vvq(_vq); + u16 last_used_idx; START_USE(vq); @@ -372,15 +385,45 @@ bool virtqueue_enable_cb(struct virtqueu * 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(); - 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); diff -upr linux-3.2.49/include/linux/virtio.h linux-3.2.49wg/include/linux/virtio.h --- linux-3.2.49/include/linux/virtio.h 2012-01-05 00:55:44.000000000 +0100 +++ linux-3.2.49wg/include/linux/virtio.h 2013-07-27 13:57:28.000000000 +0200 @@ -96,6 +96,10 @@ void virtqueue_disable_cb(struct virtque bool virtqueue_enable_cb(struct virtqueue *vq); +unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq); + +bool virtqueue_poll(struct virtqueue *vq, unsigned); + bool virtqueue_enable_cb_delayed(struct virtqueue *vq); void *virtqueue_detach_unused_buf(struct virtqueue *vq); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
