Re: [RFC 0/4] Introduce VDUSE - vDPA Device in Userspace

[Jason Wang <jasowang@redhat.com>]

On 2020/10/19 下午10:56, Xie Yongji wrote:
> This series introduces a framework, which can be used to implement
> vDPA Devices in a userspace program. To implement it, the work
> consist of two parts: control path emulating and data path offloading.
>
> In the control path, the VDUSE driver will make use of message
> mechnism to forward the actions (get/set features, get/st status,
> get/set config space and set virtqueue states) from virtio-vdpa
> driver to userspace. Userspace can use read()/write() to
> receive/reply to those control messages.
>
> In the data path, the VDUSE driver implements a MMU-based
> on-chip IOMMU driver which supports both direct mapping and
> indirect mapping with bounce buffer. Then userspace can access
> those iova space via mmap(). Besides, eventfd mechnism is used to
> trigger interrupts and forward virtqueue kicks.


This is pretty interesting!

For vhost-vdpa, it should work, but for virtio-vdpa, I think we should 
carefully deal with the IOMMU/DMA ops stuffs.

I notice that neither dma_map nor set_map is implemented in 
vduse_vdpa_config_ops, this means you want to let vhost-vDPA to deal 
with IOMMU domains stuffs.  Any reason for doing that?

The reason for the questions are:

1) You've implemented a on-chip IOMMU driver but don't expose it to 
generic IOMMU layer (or generic IOMMU layer may need some extension to 
support this)
2) We will probably remove the IOMMU domain management in vhost-vDPA, 
and move it to the device(parent).

So if it's possible, please implement either set_map() or 
dma_map()/dma_unmap(), this may align with our future goal and may speed 
up the development.

Btw, it would be helpful to give even more details on how the on-chip 
IOMMU driver in implemented.


>
> The details and our user case is shown below:
>
> ------------------------     -----------------------------------------------------------
> |                  APP |     |                          QEMU                           |
> |       ---------      |     | --------------------    -------------------+<-->+------ |
> |       |dev/vdx|      |     | | device emulation |    | virtio dataplane |    | BDS | |
> ------------+-----------     -----------+-----------------------+-----------------+-----
>              |                           |                       |                 |
>              |                           | emulating             | offloading      |
> ------------+---------------------------+-----------------------+-----------------+------
> |    | block device |           |  vduse driver |        |  vdpa device |    | TCP/IP | |
> |    -------+--------           --------+--------        +------+-------     -----+---- |
> |           |                           |                |      |                 |     |
> |           |                           |                |      |                 |     |
> | ----------+----------       ----------+-----------     |      |                 |     |
> | | virtio-blk driver |       | virtio-vdpa driver |     |      |                 |     |
> | ----------+----------       ----------+-----------     |      |                 |     |
> |           |                           |                |      |                 |     |
> |           |                           ------------------      |                 |     |
> |           -----------------------------------------------------              ---+---  |
> ------------------------------------------------------------------------------ | NIC |---
>                                                                                 ---+---
>                                                                                    |
>                                                                           ---------+---------
>                                                                           | Remote Storages |
>                                                                           -------------------


The figure is not very clear to me in the following points:

1) if the device emulation and virtio dataplane is all implemented in 
QEMU, what's the point of doing this? I thought the device should be a 
remove process?
2) it would be better to draw a vDPA bus somewhere to help people to 
understand the architecture
3) for the "offloading" I guess it should be done virtio vhost-vDPA, so 
it's better to draw a vhost-vDPA block there


> We make use of it to implement a block device connecting to
> our distributed storage, which can be used in containers and
> bare metal. Compared with qemu-nbd solution, this solution has
> higher performance, and we can have an unified technology stack
> in VM and containers for remote storages.
>
> To test it with a host disk (e.g. /dev/sdx):
>
>    $ qemu-storage-daemon \
>        --chardev socket,id=charmonitor,path=/tmp/qmp.sock,server,nowait \
>        --monitor chardev=charmonitor \
>        --blockdev driver=host_device,cache.direct=on,aio=native,filename=/dev/sdx,node-name=disk0 \
>        --export vduse-blk,id=test,node-name=disk0,writable=on,vduse-id=1,num-queues=16,queue-size=128
>
> The qemu-storage-daemon can be found at https://github.com/bytedance/qemu/tree/vduse
>
> Future work:
>    - Improve performance (e.g. zero copy implementation in datapath)
>    - Config interrupt support
>    - Userspace library (find a way to reuse device emulation code in qemu/rust-vmm)


Right, a library will be very useful.

Thanks


>
> Xie Yongji (4):
>    mm: export zap_page_range() for driver use
>    vduse: Introduce VDUSE - vDPA Device in Userspace
>    vduse: grab the module's references until there is no vduse device
>    vduse: Add memory shrinker to reclaim bounce pages
>
>   drivers/vdpa/Kconfig                 |    8 +
>   drivers/vdpa/Makefile                |    1 +
>   drivers/vdpa/vdpa_user/Makefile      |    5 +
>   drivers/vdpa/vdpa_user/eventfd.c     |  221 ++++++
>   drivers/vdpa/vdpa_user/eventfd.h     |   48 ++
>   drivers/vdpa/vdpa_user/iova_domain.c |  488 ++++++++++++
>   drivers/vdpa/vdpa_user/iova_domain.h |  104 +++
>   drivers/vdpa/vdpa_user/vduse.h       |   66 ++
>   drivers/vdpa/vdpa_user/vduse_dev.c   | 1081 ++++++++++++++++++++++++++
>   include/uapi/linux/vduse.h           |   85 ++
>   mm/memory.c                          |    1 +
>   11 files changed, 2108 insertions(+)
>   create mode 100644 drivers/vdpa/vdpa_user/Makefile
>   create mode 100644 drivers/vdpa/vdpa_user/eventfd.c
>   create mode 100644 drivers/vdpa/vdpa_user/eventfd.h
>   create mode 100644 drivers/vdpa/vdpa_user/iova_domain.c
>   create mode 100644 drivers/vdpa/vdpa_user/iova_domain.h
>   create mode 100644 drivers/vdpa/vdpa_user/vduse.h
>   create mode 100644 drivers/vdpa/vdpa_user/vduse_dev.c
>   create mode 100644 include/uapi/linux/vduse.h
>

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization