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Date: Wed, 14 Apr 2021 15:54:51 +0800
From: Yongji Xie <xieyongji@...edance.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Jason Wang <jasowang@...hat.com>,
Stefan Hajnoczi <stefanha@...hat.com>,
Stefano Garzarella <sgarzare@...hat.com>,
Parav Pandit <parav@...dia.com>,
Christoph Hellwig <hch@...radead.org>,
Christian Brauner <christian.brauner@...onical.com>,
Randy Dunlap <rdunlap@...radead.org>,
Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
Jonathan Corbet <corbet@....net>,
Mika Penttilä <mika.penttila@...tfour.com>,
Dan Carpenter <dan.carpenter@...cle.com>,
virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Re: [PATCH v6 00/10] Introduce VDUSE - vDPA Device in Userspace
On Wed, Apr 14, 2021 at 3:35 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Wed, Mar 31, 2021 at 04:05:09PM +0800, 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. And in vhost-vdpa case, the dma
> > buffer is reside in a userspace memory region which can be shared to the
> > VDUSE userspace processs via transferring the shmfd.
> >
> > The details and our user case is shown below:
> >
> > ------------------------ ------------------------- ----------------------------------------------
> > | Container | | QEMU(VM) | | VDUSE daemon |
> > | --------- | | ------------------- | | ------------------------- ---------------- |
> > | |dev/vdx| | | |/dev/vhost-vdpa-x| | | | vDPA device emulation | | block driver | |
> > ------------+----------- -----------+------------ -------------+----------------------+---------
> > | | | |
> > | | | |
> > ------------+---------------------------+----------------------------+----------------------+---------
> > | | block device | | vhost device | | vduse driver | | TCP/IP | |
> > | -------+-------- --------+-------- -------+-------- -----+---- |
> > | | | | | |
> > | ----------+---------- ----------+----------- -------+------- | |
> > | | virtio-blk driver | | vhost-vdpa driver | | vdpa device | | |
> > | ----------+---------- ----------+----------- -------+------- | |
> > | | virtio bus | | | |
> > | --------+----+----------- | | | |
> > | | | | | |
> > | ----------+---------- | | | |
> > | | virtio-blk device | | | | |
> > | ----------+---------- | | | |
> > | | | | | |
> > | -----------+----------- | | | |
> > | | virtio-vdpa driver | | | | |
> > | -----------+----------- | | | |
> > | | | | vdpa bus | |
> > | -----------+----------------------+---------------------------+------------ | |
> > | ---+--- |
> > -----------------------------------------------------------------------------------------| NIC |------
> > ---+---
> > |
> > ---------+---------
> > | Remote Storages |
> > -------------------
>
> This all looks quite similar to vhost-user-block except that one
> does not need any kernel support at all.
>
> So I am still scratching my head about its advantages over
> vhost-user-block.
>
It plays the same role as vhost-user-block in VM user cases.
>
> > We make use of it to implement a block device connecting to
> > our distributed storage, which can be used both in containers and
> > VMs. Thus, we can have an unified technology stack in this two cases.
>
> Maybe the container part is the answer. How does that stack look?
>
Yes, it enables containers to reuse virtio software stack. We can have
one daemon that provides service to both containers and virtual
machines.
Thanks，
Yongji
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