Re: [RFC v2 00/13] Introduce VDUSE - vDPA Device in Userspace

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On Wed, Dec 23, 2020 at 2:38 PM Jason Wang <jasowang@xxxxxxxxxx> wrote:
>
>
> On 2020/12/22 下午10:52, Xie Yongji wrote:
> > This series introduces a framework, which can be used to implement
> > vDPA Devices in a userspace program. The work consist of two parts:
> > control path forwarding and data path offloading.
> >
> > In the control path, the VDUSE driver will make use of message
> > mechnism to forward the config operation from vdpa bus driver
> > to userspace. Userspace can use read()/write() to receive/reply
> > those control messages.
> >
> > In the data path, the core is mapping dma buffer into VDUSE
> > daemon's address space, which can be implemented in different ways
> > depending on the vdpa bus to which the vDPA device is attached.
> >
> > In virtio-vdpa case, we implements a MMU-based on-chip IOMMU driver with
> > bounce-buffering mechanism to achieve that.
>
>
> Rethink about the bounce buffer stuffs. I wonder instead of using kernel
> pages with mmap(), how about just use userspace pages like what vhost did?
>
> It means we need a worker to do bouncing but we don't need to care about
> annoying stuffs like page reclaiming?
>

Now the I/O bouncing is done in the streaming DMA mapping routines
which can be called from interrupt context. If we put this into a
kworker, that means we need to synchronize with a kworker in an
interrupt context. I think it can't work.

Thanks,
Yongji




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