Re: [PATCH v8 09/10] vduse: Introduce VDUSE - vDPA Device in Userspace

在 2021/7/1 下午6:26, Yongji Xie 写道:

On Thu, Jul 1, 2021 at 3:55 PM Jason Wang [off-list ref] wrote:

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在 2021/7/1 下午2:50, Yongji Xie 写道:

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On Wed, Jun 30, 2021 at 5:51 PM Stefan Hajnoczi [off-list ref] wrote:

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On Tue, Jun 29, 2021 at 10:59:51AM +0800, Yongji Xie wrote:

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On Mon, Jun 28, 2021 at 9:02 PM Stefan Hajnoczi [off-list ref] wrote:

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On Tue, Jun 15, 2021 at 10:13:30PM +0800, Xie Yongji wrote:

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+/* ioctls */
+
+struct vduse_dev_config {
+     char name[VDUSE_NAME_MAX]; /* vduse device name */
+     __u32 vendor_id; /* virtio vendor id */
+     __u32 device_id; /* virtio device id */
+     __u64 features; /* device features */
+     __u64 bounce_size; /* bounce buffer size for iommu */
+     __u16 vq_size_max; /* the max size of virtqueue */

The VIRTIO specification allows per-virtqueue sizes. A device can have
two virtqueues, where the first one allows up to 1024 descriptors and
the second one allows only 128 descriptors, for example.

Good point! But it looks like virtio-vdpa/virtio-pci doesn't support
that now. All virtqueues have the same maximum size.

I see struct vpda_config_ops only supports a per-device max vq size:
u16 (*get_vq_num_max)(struct vdpa_device *vdev);

virtio-pci supports per-virtqueue sizes because the struct
virtio_pci_common_cfg->queue_size register is per-queue (controlled by
queue_select).

Oh, yes. I miss queue_select.

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I guess this is a question for Jason: will vdpa will keep this limitation?
If yes, then VDUSE can stick to it too without running into problems in
the future.

I think it's better to extend the get_vq_num_max() per virtqueue.

Currently, vDPA assumes the parent to have a global max size. This seems
to work on most of the parents but not vp-vDPA (which could be backed by
QEMU, in that case cvq's size is smaller).

Fortunately, we haven't enabled had cvq support in the userspace now.

I can post the fixes.

OK. If so, it looks like we need to support the per-vq configuration.
I wonder if it's better to use something like: VDUSE_CREATE_DEVICE ->
VDUSE_SETUP_VQ -> VDUSE_SETUP_VQ -> ... -> VDUSE_ENABLE_DEVICE to do
initialization rather than only use VDUSE_CREATE_DEVICE.

This should be fine.

Thanks

Thanks,
Yongji