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References: <20221205084127.535-1-xieyongji@bytedance.com> <20221205090243.791-1-xieyongji@bytedance.com>
 <20221205090243.791-3-xieyongji@bytedance.com>
In-Reply-To: <20221205090243.791-3-xieyongji@bytedance.com>
From:   Jason Wang <jasowang@redhat.com>
Date:   Fri, 16 Dec 2022 13:43:00 +0800
Message-ID: <CACGkMEuAxEEvShwN8Q_k-FKZODesORn4zJG7UFHD-KS8sQXYjg@mail.gmail.com>
Subject: Re: [PATCH v2 09/11] vduse: Add enable_irq_wq sysfs interface for virtqueues
To:     Xie Yongji <xieyongji@bytedance.com>
Cc:     mst@redhat.com, tglx@linutronix.de, hch@lst.de,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org
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On Mon, Dec 5, 2022 at 5:03 PM Xie Yongji <xieyongji@bytedance.com> wrote:
>
> Add enable_irq_wq sysfs interface to control whether
> use workqueue to inject irq or not. The vhost-vdpa case
> can benefit from it.

Do we have a benchmark result for this?

Or I wonder if we can extend set_vq_cb() by associating an eventfd
then VDUSE can signal that eventfd directly?

Thanks

>
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 50 +++++++++++++++++++++++++++++-
>  1 file changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index c65f84100e30..ed06c7afd484 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -62,6 +62,7 @@ struct vduse_virtqueue {
>         struct cpumask irq_affinity;
>         spinlock_t irq_affinity_lock;
>         struct kobject kobj;
> +       bool enable_irq_wq;
>  };
>
>  struct vduse_dev;
> @@ -1013,6 +1014,26 @@ static int vduse_dev_queue_irq_work(struct vduse_dev *dev,
>         return ret;
>  }
>
> +static int vduse_dev_inject_vq_irq(struct vduse_dev *dev,
> +                                  struct vduse_virtqueue *vq)
> +{
> +       int ret = -EINVAL;
> +
> +       down_read(&dev->rwsem);
> +       if (!(dev->status & VIRTIO_CONFIG_S_DRIVER_OK))
> +               goto unlock;
> +
> +       ret = 0;
> +       spin_lock_irq(&vq->irq_lock);
> +       if (vq->ready && vq->cb.callback)
> +               vq->cb.callback(vq->cb.private);
> +       spin_unlock_irq(&vq->irq_lock);
> +unlock:
> +       up_read(&dev->rwsem);
> +
> +       return ret;
> +}
> +
>  static int vduse_dev_dereg_umem(struct vduse_dev *dev,
>                                 u64 iova, u64 size)
>  {
> @@ -1278,8 +1299,12 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
>                         break;
>
>                 index = array_index_nospec(index, dev->vq_num);
> -               ret = vduse_dev_queue_irq_work(dev, &dev->vqs[index]->inject,
> +               if (dev->vqs[index]->enable_irq_wq)
> +                       ret = vduse_dev_queue_irq_work(dev,
> +                                       &dev->vqs[index]->inject,
>                                         dev->vqs[index]->irq_effective_cpu);
> +               else
> +                       ret = vduse_dev_inject_vq_irq(dev, dev->vqs[index]);
>                 break;
>         }
>         case VDUSE_IOTLB_REG_UMEM: {
> @@ -1420,6 +1445,26 @@ static const struct file_operations vduse_dev_fops = {
>         .llseek         = noop_llseek,
>  };
>
> +static ssize_t enable_irq_wq_show(struct vduse_virtqueue *vq, char *buf)
> +{
> +       return sprintf(buf, "%d\n", vq->enable_irq_wq);
> +}
> +
> +static ssize_t enable_irq_wq_store(struct vduse_virtqueue *vq,
> +                                  const char *buf, size_t count)
> +{
> +       bool enabled;
> +       int ret;
> +
> +       ret = kstrtobool(buf, &enabled);
> +       if (ret)
> +               return ret;
> +
> +       vq->enable_irq_wq = enabled;
> +
> +       return count;
> +}
> +
>  static ssize_t irq_cb_affinity_show(struct vduse_virtqueue *vq, char *buf)
>  {
>         return sprintf(buf, "%*pb\n", cpumask_pr_args(&vq->irq_affinity));
> @@ -1480,10 +1525,12 @@ struct vq_sysfs_entry {
>  static struct vq_sysfs_entry irq_cb_affinity_attr = __ATTR_RO(irq_cb_affinity);
>  static struct vq_sysfs_entry irq_cb_effective_affinity_attr =
>                                         __ATTR_RW(irq_cb_effective_affinity);
> +static struct vq_sysfs_entry enable_irq_wq_attr = __ATTR_RW(enable_irq_wq);
>
>  static struct attribute *vq_attrs[] = {
>         &irq_cb_affinity_attr.attr,
>         &irq_cb_effective_affinity_attr.attr,
> +       &enable_irq_wq_attr.attr,
>         NULL,
>  };
>  ATTRIBUTE_GROUPS(vq);
> @@ -1565,6 +1612,7 @@ static int vduse_dev_init_vqs(struct vduse_dev *dev, u32 vq_align, u32 vq_num)
>
>                 dev->vqs[i]->index = i;
>                 dev->vqs[i]->irq_effective_cpu = -1;
> +               dev->vqs[i]->enable_irq_wq = true;
>                 INIT_WORK(&dev->vqs[i]->inject, vduse_vq_irq_inject);
>                 INIT_WORK(&dev->vqs[i]->kick, vduse_vq_kick_work);
>                 spin_lock_init(&dev->vqs[i]->kick_lock);
> --
> 2.20.1
>