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Commit cc229884 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by David S. Miller
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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: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 01276ed2

drivers/virtio/virtio_ring.c

+44 −12
Original line number Original line Diff line number Diff line
@@ -607,19 +607,21 @@ void virtqueue_disable_cb(struct virtqueue *_vq) 
EXPORT_SYMBOL_GPL(virtqueue_disable_cb);

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.

 * @vq: the struct virtqueue we're talking about.

 *

 *

 * This re-enables callbacks; it returns "false" if there are pending

 * This re-enables callbacks; it returns current queue state

 * buffers in the queue, to detect a possible race between the driver

 * in an opaque unsigned value. This value should be later tested by

 * checking for more work, and enabling callbacks.

 * 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

 * Caller must ensure we don't call this with other virtqueue

 * operations at the same time (except where noted).

 * 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);

	struct vring_virtqueue *vq = to_vvq(_vq);

	u16 last_used_idx;





	START_USE(vq);

	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

	 * either clear the flags bit or point the event index at the next

	 * entry. Always do both to keep code simple. */

	 * entry. Always do both to keep code simple. */

	vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;

	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;

	virtio_mb(vq->weak_barriers);

	if (unlikely(more_used(vq))) {

	END_USE(vq);

	END_USE(vq);

		return false;

	return last_used_idx;

}

}

EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);





	END_USE(vq);

/**

	return true;

 * 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);

	return (u16)last_used_idx != vq->vring.used->idx;

}

EXPORT_SYMBOL_GPL(virtqueue_poll);



/**

 * 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);

EXPORT_SYMBOL_GPL(virtqueue_enable_cb);

include/linux/virtio.h

+4 −0
Original line number Original line Diff line number Diff line
@@ -70,6 +70,10 @@ void virtqueue_disable_cb(struct virtqueue *vq); 




bool virtqueue_enable_cb(struct virtqueue *vq);

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);

bool virtqueue_enable_cb_delayed(struct virtqueue *vq);





void *virtqueue_detach_unused_buf(struct virtqueue *vq);

void *virtqueue_detach_unused_buf(struct virtqueue *vq);