Virtualization - Nov 2022 - [PATCH 6/6] vduse: Support specifying bounce buffer size via sysfs

On Mon, Nov 14, 2022 at 3:16 PM Xie Yongji <xieyongji at bytedance.com>
wrote:
>
> Add sysfs interface to support specifying bounce
> buffer size in virtio-vdpa case. This is a performance
> tuning parameter for high throughput workloads.
I wonder what's the reason for not having this in VDUSE_CREATE_DEV?

Thanks
>
> Signed-off-by: Xie Yongji <xieyongji at bytedance.com>
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 45 +++++++++++++++++++++++++++++-
>  1 file changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c
b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 428615093c28..3f97e2d7f7d7 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -37,8 +37,11 @@
>  #define DRV_LICENSE  "GPL v2"
>
>  #define VDUSE_DEV_MAX (1U << MINORBITS)
> +#define VDUSE_MAX_BOUNCE_SIZE (1024 * 1024 * 1024)
> +#define VDUSE_MIN_BOUNCE_SIZE (1024 * 1024)
>  #define VDUSE_BOUNCE_SIZE (64 * 1024 * 1024)
> -#define VDUSE_IOVA_SIZE (128 * 1024 * 1024)
> +/* 128 MB reserved for virtqueue creation */
> +#define VDUSE_IOVA_SIZE (VDUSE_MAX_BOUNCE_SIZE + 128 * 1024 * 1024)
>  #define VDUSE_MSG_DEFAULT_TIMEOUT 30
>
>  struct vduse_virtqueue {
> @@ -1687,8 +1690,48 @@ static ssize_t msg_timeout_store(struct device
*device,
>
>  static DEVICE_ATTR_RW(msg_timeout);
>
> +static ssize_t bounce_size_show(struct device *device,
> +                               struct device_attribute *attr, char *buf)
> +{
> +       struct vduse_dev *dev = dev_get_drvdata(device);
> +
> +       return sysfs_emit(buf, "%u\n", dev->bounce_size);
> +}
> +
> +static ssize_t bounce_size_store(struct device *device,
> +                                struct device_attribute *attr,
> +                                const char *buf, size_t count)
> +{
> +       struct vduse_dev *dev = dev_get_drvdata(device);
> +       unsigned int bounce_size;
> +       int ret;
> +
> +       ret = -EPERM;
> +       mutex_lock(&dev->domain_lock);
> +       if (dev->domain)
> +               goto unlock;
> +
> +       ret = kstrtouint(buf, 10, &bounce_size);
> +       if (ret < 0)
> +               goto unlock;
> +
> +       ret = -EINVAL;
> +       if (bounce_size > VDUSE_MAX_BOUNCE_SIZE ||
> +           bounce_size < VDUSE_MIN_BOUNCE_SIZE)
> +               goto unlock;
> +
> +       dev->bounce_size = bounce_size;
> +       ret = count;
> +unlock:
> +       mutex_unlock(&dev->domain_lock);
> +       return ret;
> +}
> +
> +static DEVICE_ATTR_RW(bounce_size);
> +
>  static struct attribute *vduse_dev_attrs[] = {
>         &dev_attr_msg_timeout.attr,
> +       &dev_attr_bounce_size.attr,
>         NULL
>  };
>
> --
> 2.20.1
>