Re: [dpdk-dev] [PATCH v3 3/3] net/vhost: fix interrupt mode

[David Marchand <david.marchand@redhat.com>]

On Wed, Jul 29, 2020 at 11:20 AM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
> At .new_device() time, only the first vring pair is
> now ready, other vrings are consfigured later.

configured*

>
> Problem is that when application will setup and enable
> interrupts, only the first queue pair Rx interrupt will
> be enabled.
>
> This patches fixes the issue by setting the number of
> max interrupts to the number of Rx queues that will be
> later initialized. Then, as soon as a Rx vring is ready
> and interrupt enabled by the application, it removes the
> corresponding uninitialized epoll event, and install a

installs*

> new one with the valid FD.
>
> Fixes: 604052ae5395 ("net/vhost: support queue update")
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

It seems a bit of a hack, but I _think_ the patch is good wrt races on
epoll configuration.

We are only touching the vhost pmd, in interrupt mode.
The interrupt mode is not that frequently used (I found no usage in
opensource projects).
The vhost pmd is not used in OVS as it lags behind the vhost library
and has limitations.

So my opinion is that the risk of taking this patch rather than
reverting the changes (which is not trivial iiuc) in the vhost library
is acceptable.


One comment below:

> ---
>  drivers/net/vhost/rte_eth_vhost.c | 75 +++++++++++++++++++++++++++----
>  1 file changed, 66 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/vhost/rte_eth_vhost.c b/drivers/net/vhost/rte_eth_vhost.c
> index 951929c663..237785dd66 100644
> --- a/drivers/net/vhost/rte_eth_vhost.c
> +++ b/drivers/net/vhost/rte_eth_vhost.c
> @@ -5,6 +5,7 @@
>  #include <unistd.h>
>  #include <pthread.h>
>  #include <stdbool.h>
> +#include <sys/epoll.h>
>
>  #include <rte_mbuf.h>
>  #include <rte_ethdev_driver.h>
> @@ -95,6 +96,8 @@ struct vhost_queue {
>         uint16_t port;
>         uint16_t virtqueue_id;
>         struct vhost_stats stats;
> +       int intr_enable;
> +       rte_spinlock_t intr_lock;
>  };
>
>  struct pmd_internal {
> @@ -524,6 +527,45 @@ find_internal_resource(char *ifname)
>         return list;
>  }
>
> +static int
> +eth_vhost_update_intr(struct rte_eth_dev *eth_dev, uint16_t rxq_idx)
> +{
> +       struct rte_intr_handle *handle = eth_dev->intr_handle;
> +       struct rte_epoll_event rev;
> +       int epfd, ret;
> +
> +       if (handle->efds[rxq_idx] == handle->elist[rxq_idx].fd)
> +               return 0;

Feel free to ignore if this situation can not happen.

We are expecting only -1 -> valid fd transitions.
Maybe add an error log if we are in another situation?
This would indicate something quite broken.



> +
> +       VHOST_LOG(INFO, "kickfd for rxq-%d was changed, updating handler.\n",
> +                       rxq_idx);
> +
> +       /*
> +        * First remove invalid epoll event, and then isntall
> +        * the new one. May be solved with a proper API in the
> +        * future.
> +        */
> +       epfd = handle->elist[rxq_idx].epfd;
> +       rev = handle->elist[rxq_idx];
> +       ret = rte_epoll_ctl(epfd, EPOLL_CTL_DEL, rev.fd,
> +                       &handle->elist[rxq_idx]);
> +       if (ret) {
> +               VHOST_LOG(ERR, "Delete epoll event failed.\n");
> +               return ret;
> +       }
> +
> +       rev.fd = handle->efds[rxq_idx];
> +       handle->elist[rxq_idx] = rev;
> +       ret = rte_epoll_ctl(epfd, EPOLL_CTL_ADD, rev.fd,
> +                       &handle->elist[rxq_idx]);
> +       if (ret) {
> +               VHOST_LOG(ERR, "Add epoll event failed.\n");
> +               return ret;
> +       }
> +
> +       return 0;
> +}
> +
>  static int
>  eth_rxq_intr_enable(struct rte_eth_dev *dev, uint16_t qid)
>  {
> @@ -537,6 +579,11 @@ eth_rxq_intr_enable(struct rte_eth_dev *dev, uint16_t qid)
>                 return -1;
>         }
>
> +       rte_spinlock_lock(&vq->intr_lock);
> +       vq->intr_enable = 1;
> +       ret = eth_vhost_update_intr(dev, qid);
> +       rte_spinlock_unlock(&vq->intr_lock);
> +
>         ret = rte_vhost_get_vhost_vring(vq->vid, (qid << 1) + 1, &vring);
>         if (ret < 0) {
>                 VHOST_LOG(ERR, "Failed to get rxq%d's vring\n", qid);
> @@ -571,6 +618,8 @@ eth_rxq_intr_disable(struct rte_eth_dev *dev, uint16_t qid)
>         rte_vhost_enable_guest_notification(vq->vid, (qid << 1) + 1, 0);
>         rte_wmb();
>
> +       vq->intr_enable = 0;
> +
>         return 0;
>  }
>
> @@ -593,7 +642,6 @@ eth_vhost_install_intr(struct rte_eth_dev *dev)
>  {
>         struct rte_vhost_vring vring;
>         struct vhost_queue *vq;
> -       int count = 0;
>         int nb_rxq = dev->data->nb_rx_queues;
>         int i;
>         int ret;
> @@ -623,6 +671,8 @@ eth_vhost_install_intr(struct rte_eth_dev *dev)
>
>         VHOST_LOG(INFO, "Prepare intr vec\n");
>         for (i = 0; i < nb_rxq; i++) {
> +               dev->intr_handle->intr_vec[i] = RTE_INTR_VEC_RXTX_OFFSET + i;
> +               dev->intr_handle->efds[i] = -1;
>                 vq = dev->data->rx_queues[i];
>                 if (!vq) {
>                         VHOST_LOG(INFO, "rxq-%d not setup yet, skip!\n", i);
> @@ -641,14 +691,12 @@ eth_vhost_install_intr(struct rte_eth_dev *dev)
>                                 "rxq-%d's kickfd is invalid, skip!\n", i);
>                         continue;
>                 }
> -               dev->intr_handle->intr_vec[i] = RTE_INTR_VEC_RXTX_OFFSET + i;
>                 dev->intr_handle->efds[i] = vring.kickfd;
> -               count++;
>                 VHOST_LOG(INFO, "Installed intr vec for rxq-%d\n", i);
>         }
>
> -       dev->intr_handle->nb_efd = count;
> -       dev->intr_handle->max_intr = count + 1;
> +       dev->intr_handle->nb_efd = nb_rxq;
> +       dev->intr_handle->max_intr = nb_rxq + 1;
>         dev->intr_handle->type = RTE_INTR_HANDLE_VDEV;
>
>         return 0;
> @@ -835,6 +883,7 @@ vring_conf_update(int vid, struct rte_eth_dev *eth_dev, uint16_t vring_id)
>  {
>         struct rte_eth_conf *dev_conf = &eth_dev->data->dev_conf;
>         struct pmd_internal *internal = eth_dev->data->dev_private;
> +       struct vhost_queue *vq;
>         struct rte_vhost_vring vring;
>         int rx_idx = vring_id % 2 ? (vring_id - 1) >> 1 : -1;
>         int ret = 0;
> @@ -853,12 +902,18 @@ vring_conf_update(int vid, struct rte_eth_dev *eth_dev, uint16_t vring_id)
>                                         vring_id);
>                         return ret;
>                 }
> +               eth_dev->intr_handle->efds[rx_idx] = vring.kickfd;
>
> -               if (vring.kickfd != eth_dev->intr_handle->efds[rx_idx]) {
> -                       VHOST_LOG(INFO, "kickfd for rxq-%d was changed.\n",
> -                                         rx_idx);
> -                       eth_dev->intr_handle->efds[rx_idx] = vring.kickfd;
> +               vq = eth_dev->data->rx_queues[rx_idx];
> +               if (!vq) {
> +                       VHOST_LOG(ERR, "rxq%d is not setup yet\n", rx_idx);
> +                       return -1;
>                 }
> +
> +               rte_spinlock_lock(&vq->intr_lock);
> +               if (vq->intr_enable)
> +                       ret = eth_vhost_update_intr(eth_dev, rx_idx);
> +               rte_spinlock_unlock(&vq->intr_lock);
>         }
>
>         return ret;
> @@ -1152,6 +1207,7 @@ eth_rx_queue_setup(struct rte_eth_dev *dev, uint16_t rx_queue_id,
>
>         vq->mb_pool = mb_pool;
>         vq->virtqueue_id = rx_queue_id * VIRTIO_QNUM + VIRTIO_TXQ;
> +       rte_spinlock_init(&vq->intr_lock);
>         dev->data->rx_queues[rx_queue_id] = vq;
>
>         return 0;
> @@ -1173,6 +1229,7 @@ eth_tx_queue_setup(struct rte_eth_dev *dev, uint16_t tx_queue_id,
>         }
>
>         vq->virtqueue_id = tx_queue_id * VIRTIO_QNUM + VIRTIO_RXQ;
> +       rte_spinlock_init(&vq->intr_lock);
>         dev->data->tx_queues[tx_queue_id] = vq;
>
>         return 0;
> --
> 2.26.2
>



--
David Marchand