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virtio: support unlocked queue kick

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Based on patch by Christoph for virtio_blk speedup:

	Split virtqueue_kick to be able to do the actual notification
	outside the lock protecting the virtqueue.  This patch was
	originally done by Stefan Hajnoczi, but I can't find the
	original one anymore and had to recreated it from memory.
	Pointers to the original or corrections for the commit message
	are welcome.

Stefan's patch was here:

	a6d06644e3
	http://www.spinics.net/lists/linux-virtualization/msg14616.html

Third time's the charm!

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell 2012-01-12 15:44:43 +10:30
parent f96fde41f7
commit 41f0377f73
2 changed files with 52 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

60
drivers/virtio/virtio_ring.c
View file

@ -262,19 +262,22 @@ int virtqueue_add_buf(struct virtqueue *_vq,
EXPORT_SYMBOL_GPL(virtqueue_add_buf);
/**
* virtqueue_kick - update after add_buf
* virtqueue_kick_prepare - first half of split virtqueue_kick call.
* @vq: the struct virtqueue
*
* After one or more virtqueue_add_buf calls, invoke this to kick
* the other side.
* Instead of virtqueue_kick(), you can do:
* if (virtqueue_kick_prepare(vq))
* virtqueue_notify(vq);
*
* Caller must ensure we don't call this with other virtqueue
* operations at the same time (except where noted).
* This is sometimes useful because the virtqueue_kick_prepare() needs
* to be serialized, but the actual virtqueue_notify() call does not.
*/
void virtqueue_kick(struct virtqueue *_vq)
bool virtqueue_kick_prepare(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
u16 new, old;
bool needs_kick;
START_USE(vq);
/* Descriptors and available array need to be set before we expose the
* new available array entries. */
@ -287,13 +290,46 @@ void virtqueue_kick(struct virtqueue *_vq)
/* Need to update avail index before checking if we should notify */
virtio_mb(vq);
if (vq->event ?
vring_need_event(vring_avail_event(&vq->vring), new, old) :
!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
/* Prod other side to tell it about changes. */
vq->notify(&vq->vq);
if (vq->event) {
needs_kick = vring_need_event(vring_avail_event(&vq->vring),
new, old);
} else {
needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
}
END_USE(vq);
return needs_kick;
}
EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
/**
* virtqueue_notify - second half of split virtqueue_kick call.
* @vq: the struct virtqueue
*
* This does not need to be serialized.
*/
void virtqueue_notify(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
/* Prod other side to tell it about changes. */
vq->notify(_vq);
}
EXPORT_SYMBOL_GPL(virtqueue_notify);
/**
* virtqueue_kick - update after add_buf
* @vq: the struct virtqueue
*
* After one or more virtqueue_add_buf calls, invoke this to kick
* the other side.
*
* Caller must ensure we don't call this with other virtqueue
* operations at the same time (except where noted).
*/
void virtqueue_kick(struct virtqueue *vq)
{
if (virtqueue_kick_prepare(vq))
virtqueue_notify(vq);
}
EXPORT_SYMBOL_GPL(virtqueue_kick);

4
include/linux/virtio.h
View file

@ -34,6 +34,10 @@ int virtqueue_add_buf(struct virtqueue *vq,
void virtqueue_kick(struct virtqueue *vq);
bool virtqueue_kick_prepare(struct virtqueue *vq);
void virtqueue_notify(struct virtqueue *vq);
void *virtqueue_get_buf(struct virtqueue *vq, unsigned int *len);
void virtqueue_disable_cb(struct virtqueue *vq);