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    SubjectRe: [PATCH V5 4/6 net-next] vhost: vhost TX zero-copy support
    On Tue, May 17, 2011 at 01:50:19PM -0700, Shirley Ma wrote:
    > Resubmit the patch with most update. This patch passed some
    > live-migration test against RHEL6.2. I will run more stress test w/i
    > live migration.

    What changed from the last version?

    > Signed-off-by: Shirley Ma <xma@us.ibm.com>
    > ---
    >
    > drivers/vhost/net.c | 37 +++++++++++++++++++++++++++++++-
    > drivers/vhost/vhost.c | 55 ++++++++++++++++++++++++++++++++++++++++++++++++-
    > drivers/vhost/vhost.h | 12 ++++++++++
    > 3 files changed, 101 insertions(+), 3 deletions(-)
    >
    > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
    > index 2f7c76a..6bd6e28 100644
    > --- a/drivers/vhost/net.c
    > +++ b/drivers/vhost/net.c
    > @@ -32,6 +32,9 @@
    > * 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_ZEROCOPY_PEND 128
    > +
    > enum {
    > VHOST_NET_VQ_RX = 0,
    > VHOST_NET_VQ_TX = 1,
    > @@ -129,6 +132,7 @@ 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 +155,10 @@ 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_ZEROCOPY_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 +174,13 @@ static void handle_tx(struct vhost_net *net)
    > set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
    > break;
    > }
    > + /* If more outstanding DMAs, queue the work */
    > + if (sock_flag(sock->sk, SOCK_ZEROCOPY) &&
    > + (atomic_read(&vq->refcnt) > VHOST_MAX_ZEROCOPY_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;
    > @@ -188,17 +203,35 @@ 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 <= 128)
    > + 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;
    > + }
    > /* TODO: Check specific error and bomb out unless ENOBUFS? */
    > err = sock->ops->sendmsg(NULL, sock, &msg, len);
    > if (unlikely(err < 0)) {
    > - vhost_discard_vq_desc(vq, 1);
    > + if (!sock_flag(sock->sk, SOCK_ZEROCOPY))
    > + vhost_discard_vq_desc(vq, 1);
    > tx_poll_start(net, sock);
    > break;
    > }
    > 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..ce799d6 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)
    > @@ -230,7 +233,7 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
    > UIO_MAXIOV, GFP_KERNEL);
    > dev->vqs[i].log = kmalloc(sizeof *dev->vqs[i].log * UIO_MAXIOV,
    > GFP_KERNEL);
    > - dev->vqs[i].heads = kmalloc(sizeof *dev->vqs[i].heads *
    > + dev->vqs[i].heads = kzalloc(sizeof *dev->vqs[i].heads *
    > UIO_MAXIOV, GFP_KERNEL);
    >
    > if (!dev->vqs[i].indirect || !dev->vqs[i].log ||
    > @@ -385,6 +388,38 @@ long vhost_dev_reset_owner(struct vhost_dev *dev)
    > return 0;
    > }
    >
    > +/*
    > + comments
    > +*/
    > +void vhost_zerocopy_signal_used(struct vhost_virtqueue *vq, bool shutdown)
    > +{
    > + int i, j = 0;
    > +
    > + i = vq->done_idx;
    > + while (i != vq->upend_idx) {
    > + if ((vq->heads[i].len == VHOST_DMA_DONE_LEN) || shutdown) {
    > + /* reset len = 0 */
    > + vq->heads[i].len = 0;
    > + i = (i + 1) % UIO_MAXIOV;
    > + ++j;
    > + } else
    > + break;
    > + }
    > + if (j) {
    > + /* comments */
    > + if (i > vq->done_idx)
    > + vhost_add_used_n(vq, &vq->heads[vq->done_idx], j);
    > + else {
    > + vhost_add_used_n(vq, &vq->heads[vq->done_idx],
    > + UIO_MAXIOV - vq->done_idx);
    > + vhost_add_used_n(vq, vq->heads, i);
    > + }
    > + vq->done_idx = i;
    > + vhost_signal(vq->dev, vq);
    > + atomic_sub(j, &vq->refcnt);
    > + }
    > +}
    > +
    > /* Caller should have device mutex */
    > void vhost_dev_cleanup(struct vhost_dev *dev)
    > {
    > @@ -395,6 +430,11 @@ 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, then notify guest */
    > + if (atomic_read(&dev->vqs[i].refcnt)) {
    > + 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 +643,10 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
    >
    > mutex_lock(&vq->mutex);
    >
    > + /* force all lower device DMAs done */
    > + 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 +1460,12 @@ 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..8e3ecc7 100644
    > --- a/drivers/vhost/vhost.h
    > +++ b/drivers/vhost/vhost.h
    > @@ -13,6 +13,10 @@
    > #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
    > +
    > struct vhost_device;
    >
    > struct vhost_work;
    > @@ -108,6 +112,12 @@ 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 */
    > + /* copy of avail idx to monitor outstanding DMA zerocopy buffers */
    > + int upend_idx;
    > + /* copy of used idx to monintor DMA done zerocopy buffers */
    > + int done_idx;
    > };
    >
    > struct vhost_dev {
    > @@ -154,6 +164,8 @@ 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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