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Date: Tue, 12 Jul 2011 01:04:50 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Shirley Ma <mashirle@...ibm.com>
Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH RFC] vhost: address fixme in vhost TX zero-copy support
So the following should do it, on top of Shirleys's patch, I think. I'm
a bit not sure about using vq->upend_idx - vq->done_idx to check the
number of outstanding DMA, Shirley, what do you think?
Untested.
I'm also thinking about making the use of this conditinal
on a module parameter, off by default to reduce
stability risk while still enabling more people to
test the feature.
Thoughts?
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 7de0c6e..cf8deb3 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -156,8 +156,7 @@ static void handle_tx(struct vhost_net *net)
for (;;) {
/* Release DMAs done buffers first */
- if (atomic_read(&vq->refcnt) > VHOST_MAX_PEND)
- vhost_zerocopy_signal_used(vq);
+ vhost_zerocopy_signal_used(vq);
head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
ARRAY_SIZE(vq->iov),
@@ -175,7 +174,7 @@ static void handle_tx(struct vhost_net *net)
break;
}
/* If more outstanding DMAs, queue the work */
- if (atomic_read(&vq->refcnt) > VHOST_MAX_PEND) {
+ if (vq->upend_idx - vq->done_idx > VHOST_MAX_PEND) {
tx_poll_start(net, sock);
set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;
@@ -214,12 +213,12 @@ static void handle_tx(struct vhost_net *net)
vq->heads[vq->upend_idx].len = len;
ubuf->callback = vhost_zerocopy_callback;
- ubuf->arg = vq;
+ ubuf->arg = vq->ubufs;
ubuf->desc = vq->upend_idx;
msg.msg_control = ubuf;
msg.msg_controllen = sizeof(ubuf);
+ kref_get(&vq->ubufs->kref);
}
- atomic_inc(&vq->refcnt);
vq->upend_idx = (vq->upend_idx + 1) % UIO_MAXIOV;
}
/* TODO: Check specific error and bomb out unless ENOBUFS? */
@@ -646,6 +645,7 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
{
struct socket *sock, *oldsock;
struct vhost_virtqueue *vq;
+ struct vhost_ubuf_ref *ubufs, *oldubufs = NULL;
int r;
mutex_lock(&n->dev.mutex);
@@ -675,6 +675,13 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
oldsock = rcu_dereference_protected(vq->private_data,
lockdep_is_held(&vq->mutex));
if (sock != oldsock) {
+ ubufs = vhost_ubuf_alloc(vq, sock);
+ if (IS_ERR(ubufs)) {
+ r = PTR_ERR(ubufs);
+ goto err_ubufs;
+ }
+ oldubufs = vq->ubufs;
+ vq->ubufs = ubufs;
vhost_net_disable_vq(n, vq);
rcu_assign_pointer(vq->private_data, sock);
vhost_net_enable_vq(n, vq);
@@ -682,6 +689,9 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
mutex_unlock(&vq->mutex);
+ if (oldbufs)
+ vhost_ubuf_put_and_wait(oldbufs);
+
if (oldsock) {
vhost_net_flush_vq(n, index);
fput(oldsock->file);
@@ -690,6 +700,8 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
mutex_unlock(&n->dev.mutex);
return 0;
+err_ubufs:
+ fput(sock);
err_vq:
mutex_unlock(&vq->mutex);
err:
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index db242b1..81b1dd7 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -181,7 +181,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->log_ctx = NULL;
vq->upend_idx = 0;
vq->done_idx = 0;
- atomic_set(&vq->refcnt, 0);
+ vq->ubufs = NULL;
}
static int vhost_worker(void *data)
@@ -401,7 +401,7 @@ long vhost_dev_reset_owner(struct vhost_dev *dev)
* of used idx. Once lower device DMA done contiguously, we will signal KVM
* guest used idx.
*/
-void vhost_zerocopy_signal_used(struct vhost_virtqueue *vq)
+int vhost_zerocopy_signal_used(struct vhost_virtqueue *vq)
{
int i, j = 0;
@@ -414,10 +414,9 @@ void vhost_zerocopy_signal_used(struct vhost_virtqueue *vq)
} else
break;
}
- if (j) {
+ if (j)
vq->done_idx = i;
- atomic_sub(j, &vq->refcnt);
- }
+ return j;
}
/* Caller should have device mutex */
@@ -430,9 +429,13 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
vhost_poll_stop(&dev->vqs[i].poll);
vhost_poll_flush(&dev->vqs[i].poll);
}
- /* Wait for all lower device DMAs done (busywait FIXME) */
- while (atomic_read(&dev->vqs[i].refcnt))
- vhost_zerocopy_signal_used(&dev->vqs[i]);
+ /* Wait for all lower device DMAs done. */
+ if (dev->vqs[i].ubufs)
+ vhost_ubuf_put_and_wait(dev->vqs[i].ubufs);
+
+ /* Signal guest as appropriate. */
+ vhost_zerocopy_signal_used(&dev->vqs[i]);
+
if (dev->vqs[i].error_ctx)
eventfd_ctx_put(dev->vqs[i].error_ctx);
if (dev->vqs[i].error)
@@ -645,11 +648,6 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
mutex_lock(&vq->mutex);
- /* clean up lower device outstanding DMAs, before setting ring
- busywait FIXME */
- while (atomic_read(&vq->refcnt))
- vhost_zerocopy_signal_used(vq);
-
switch (ioctl) {
case VHOST_SET_VRING_NUM:
/* Resizing ring with an active backend?
@@ -1525,12 +1523,46 @@ void vhost_disable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
}
}
+static void vhost_zerocopy_done_signal(struct kref *kref)
+{
+ struct vhost_ubuf_ref *ubufs = container_of(kref, struct vhost_ubuf_ref,
+ kref);
+ wake_up(&ubufs->wait);
+}
+
+struct vhost_ubuf_ref *vhost_ubuf_alloc(struct vhost_virtqueue *vq,
+ void * private_data)
+{
+ struct vhost_ubuf_ref *ubufs;
+ /* No backend? Nothing to count. */
+ if (!private_data)
+ return NULL;
+ ubufs = kmalloc(sizeof *ubufs, GFP_KERNEL);
+ if (!ubufs)
+ return ERR_PTR(-ENOMEM);
+ kref_init(&ubufs->kref);
+ kref_get(&ubufs->kref);
+ init_waitqueue_head(&ubufs->wait);
+ ubufs->vq = vq;
+ return ubufs;
+}
+
+void vhost_ubuf_put_and_wait(struct vhost_ubuf_ref *ubufs)
+{
+ kref_put(&ubufs->kref, vhost_zerocopy_done_signal);
+ wait_event(ubufs->wait, !atomic_read(&ubufs->kref.refcount));
+ kfree(ubufs);
+}
+
void vhost_zerocopy_callback(void *arg)
{
struct ubuf_info *ubuf = (struct ubuf_info *)arg;
+ struct vhost_ubuf_ref *ubufs;
struct vhost_virtqueue *vq;
- vq = (struct vhost_virtqueue *)ubuf->arg;
+ ubufs = ubuf->arg;
+ vq = ubufs->vq;
/* set len = 1 to mark this desc buffers done DMA */
vq->heads[ubuf->desc].len = VHOST_DMA_DONE_LEN;
+ kref_put(&ubufs->kref, vhost_zerocopy_done_signal);
}
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 883688c..b42b126 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -55,6 +55,17 @@ struct vhost_log {
u64 len;
};
+struct vhost_virtqueue;
+
+struct vhost_ubuf_ref {
+ struct kref kref;
+ wait_queue_t wait;
+ struct vhost_virtqueue *vq;
+};
+
+struct vhost_ubuf_ref *vhost_ubuf_alloc(struct vhost_virtqueue *, void *);
+void vhost_ubuf_put_and_wait(struct vhost_ubuf_ref *);
+
/* The virtqueue structure describes a queue attached to a device. */
struct vhost_virtqueue {
struct vhost_dev *dev;
@@ -127,6 +138,9 @@ struct vhost_virtqueue {
int done_idx;
/* an array of userspace buffers info */
struct ubuf_info *ubuf_info;
+ /* Reference counting for outstanding ubufs.
+ * Protected by vq mutex. Writers must also take device mutex. */
+ struct vhost_ubuf_ref *ubufs;
};
struct vhost_dev {
@@ -174,7 +188,7 @@ bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
unsigned int log_num, u64 len);
void vhost_zerocopy_callback(void *arg);
-void vhost_zerocopy_signal_used(struct vhost_virtqueue *vq);
+int vhost_zerocopy_signal_used(struct vhost_virtqueue *vq);
#define vq_err(vq, fmt, ...) do { \
pr_debug(pr_fmt(fmt), ##__VA_ARGS__); \
--
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