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Date: Tue, 17 May 2011 23:16:23 -0700
From: Shirley Ma <mashirle@...ibm.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: David Miller <davem@...emloft.net>,
Eric Dumazet <eric.dumazet@...il.com>,
Avi Kivity <avi@...hat.com>, Arnd Bergmann <arnd@...db.de>,
netdev@...r.kernel.org, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V6 4/6 net-next] vhost: vhost TX zero-copy support
Hello Michael,
Here is the update the patch based on all of your review comments except
the completion/wait for cleanup since I am worried about outstanding
DMAs would prevent vhost from shutting down. I am sending out this for
your review, and test it out later.
For error handling, I update macvtap.c so we can discard the desc even
in zero-copy case.
Signed-off-by: Shirley Ma <xma@...ibm.com>
---
drivers/vhost/net.c | 42 +++++++++++++++++++++++++++++++++++++++++-
drivers/vhost/vhost.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
drivers/vhost/vhost.h | 13 +++++++++++++
3 files changed, 103 insertions(+), 1 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 2f7c76a..e87a1f8 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -32,6 +32,10 @@
* Using this limit prevents one virtqueue from starving others. */
#define VHOST_NET_WEIGHT 0x80000
+/* MAX number of TX used buffers for outstanding zerocopy */
+#define VHOST_MAX_PEND 128
+#define VHOST_GOODCOPY_LEN PAGE_SIZE
+
enum {
VHOST_NET_VQ_RX = 0,
VHOST_NET_VQ_TX = 1,
@@ -129,6 +133,7 @@ static void handle_tx(struct vhost_net *net)
int err, wmem;
size_t hdr_size;
struct socket *sock;
+ struct skb_ubuf_info pend;
/* TODO: check that we are running from vhost_worker? */
sock = rcu_dereference_check(vq->private_data, 1);
@@ -151,6 +156,10 @@ static void handle_tx(struct vhost_net *net)
hdr_size = vq->vhost_hlen;
for (;;) {
+ /* Release DMAs done buffers first */
+ if (atomic_read(&vq->refcnt) > VHOST_MAX_PEND)
+ vhost_zerocopy_signal_used(vq, false);
+
head = vhost_get_vq_desc(&net->dev, vq, vq->iov,
ARRAY_SIZE(vq->iov),
&out, &in,
@@ -166,6 +175,12 @@ static void handle_tx(struct vhost_net *net)
set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
break;
}
+ /* If more outstanding DMAs, queue the work */
+ if (atomic_read(&vq->refcnt) > VHOST_MAX_PEND) {
+ tx_poll_start(net, sock);
+ set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
+ break;
+ }
if (unlikely(vhost_enable_notify(vq))) {
vhost_disable_notify(vq);
continue;
@@ -188,6 +203,30 @@ static void handle_tx(struct vhost_net *net)
iov_length(vq->hdr, s), hdr_size);
break;
}
+ /* use msg_control to pass vhost zerocopy ubuf info to skb */
+ if (sock_flag(sock->sk, SOCK_ZEROCOPY)) {
+ vq->heads[vq->upend_idx].id = head;
+ if (len < VHOST_GOODCOPY_LEN)
+ /* copy don't need to wait for DMA done */
+ vq->heads[vq->upend_idx].len =
+ VHOST_DMA_DONE_LEN;
+ else {
+ vq->heads[vq->upend_idx].len = len;
+ pend.callback = vhost_zerocopy_callback;
+ pend.arg = vq;
+ pend.desc = vq->upend_idx;
+ msg.msg_control = &pend;
+ msg.msg_controllen = sizeof(pend);
+ }
+ atomic_inc(&vq->refcnt);
+ vq->upend_idx = (vq->upend_idx + 1) % UIO_MAXIOV;
+ /* if upend_idx is full, then wait for free more */
+ if (vq->upend_idx == vq->done_idx) {
+ tx_poll_start(net, sock);
+ set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
+ break;
+ }
+ }
/* TODO: Check specific error and bomb out unless ENOBUFS? */
err = sock->ops->sendmsg(NULL, sock, &msg, len);
if (unlikely(err < 0)) {
@@ -198,7 +237,8 @@ static void handle_tx(struct vhost_net *net)
if (err != len)
pr_debug("Truncated TX packet: "
" len %d != %zd\n", err, len);
- vhost_add_used_and_signal(&net->dev, vq, head, 0);
+ if (!sock_flag(sock->sk, SOCK_ZEROCOPY))
+ vhost_add_used_and_signal(&net->dev, vq, head, 0);
total_len += len;
if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
vhost_poll_queue(&vq->poll);
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 2ab2912..f4c2730 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -174,6 +174,9 @@ static void vhost_vq_reset(struct vhost_dev *dev,
vq->call_ctx = NULL;
vq->call = NULL;
vq->log_ctx = NULL;
+ vq->upend_idx = 0;
+ vq->done_idx = 0;
+ atomic_set(&vq->refcnt, 0);
}
static int vhost_worker(void *data)
@@ -385,16 +388,49 @@ long vhost_dev_reset_owner(struct vhost_dev *dev)
return 0;
}
+/* In case of DMA done not in order in lower device driver for some reason.
+ * upend_idx is used to track end of used idx, done_idx is used to track head
+ * 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, bool shutdown)
+{
+ int i, j = 0;
+
+ for (i = vq->done_idx; i != vq->upend_idx; i = i++ % UIO_MAXIOV) {
+ if ((vq->heads[i].len == VHOST_DMA_DONE_LEN) || shutdown) {
+ vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
+ vhost_add_used_and_signal(vq->dev, vq,
+ vq->heads[i].id, 0);
+ ++j;
+ } else
+ break;
+ }
+ if (j) {
+ vq->done_idx = i;
+ atomic_sub(j, &vq->refcnt);
+ }
+}
+
/* Caller should have device mutex */
void vhost_dev_cleanup(struct vhost_dev *dev)
{
int i;
+ unsigned long begin = jiffies;
for (i = 0; i < dev->nvqs; ++i) {
if (dev->vqs[i].kick && dev->vqs[i].handle_kick) {
vhost_poll_stop(&dev->vqs[i].poll);
vhost_poll_flush(&dev->vqs[i].poll);
}
+ /* Wait for all lower device DMAs done, then notify virtio_net
+ * or just notify it without waiting for all DMA done here ?
+ * in case of DMAs never done for some reason */
+ if (atomic_read(&dev->vqs[i].refcnt)) {
+ /* how long should we wait ? */
+ msleep(1000);
+ vhost_zerocopy_signal_used(&dev->vqs[i], true);
+ }
if (dev->vqs[i].error_ctx)
eventfd_ctx_put(dev->vqs[i].error_ctx);
if (dev->vqs[i].error)
@@ -603,6 +639,10 @@ 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 */
+ if (atomic_read(&vq->refcnt))
+ vhost_zerocopy_signal_used(vq, true);
+
switch (ioctl) {
case VHOST_SET_VRING_NUM:
/* Resizing ring with an active backend?
@@ -1416,3 +1456,12 @@ void vhost_disable_notify(struct vhost_virtqueue *vq)
vq_err(vq, "Failed to enable notification at %p: %d\n",
&vq->used->flags, r);
}
+
+void vhost_zerocopy_callback(struct sk_buff *skb)
+{
+ int idx = skb_shinfo(skb)->ubuf.desc;
+ struct vhost_virtqueue *vq = skb_shinfo(skb)->ubuf.arg;
+
+ /* set len = 1 to mark this desc buffers done DMA */
+ vq->heads[idx].len = VHOST_DMA_DONE_LEN;
+}
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index b3363ae..d0e7ac6 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -13,6 +13,11 @@
#include <linux/virtio_ring.h>
#include <asm/atomic.h>
+/* This is for zerocopy, used buffer len is set to 1 when lower device DMA
+ * done */
+#define VHOST_DMA_DONE_LEN 1
+#define VHOST_DMA_CLEAR_LEN 0
+
struct vhost_device;
struct vhost_work;
@@ -108,6 +113,12 @@ struct vhost_virtqueue {
/* Log write descriptors */
void __user *log_base;
struct vhost_log *log;
+ /* vhost zerocopy support */
+ atomic_t refcnt; /* num of outstanding zerocopy DMAs */
+ /* last used idx for outstanding DMA zerocopy buffers */
+ int upend_idx;
+ /* first used idx for DMA done zerocopy buffers */
+ int done_idx;
};
struct vhost_dev {
@@ -154,6 +165,8 @@ bool vhost_enable_notify(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(struct sk_buff *skb);
+void vhost_zerocopy_signal_used(struct vhost_virtqueue *vq, bool shutdown);
#define vq_err(vq, fmt, ...) do { \
pr_debug(pr_fmt(fmt), ##__VA_ARGS__); \
--
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