On Wed, Dec 2, 2020 at 12:53 PM Parav Pandit <pa...@nvidia.com> wrote: > > > > > From: Yongji Xie <xieyon...@bytedance.com> > > Sent: Wednesday, December 2, 2020 9:00 AM > > > > On Tue, Dec 1, 2020 at 11:59 PM Parav Pandit <pa...@nvidia.com> wrote: > > > > > > > > > > > > > From: Yongji Xie <xieyon...@bytedance.com> > > > > Sent: Tuesday, December 1, 2020 7:49 PM > > > > > > > > On Tue, Dec 1, 2020 at 7:32 PM Parav Pandit <pa...@nvidia.com> wrote: > > > > > > > > > > > > > > > > > > > > > From: Yongji Xie <xieyon...@bytedance.com> > > > > > > Sent: Tuesday, December 1, 2020 3:26 PM > > > > > > > > > > > > On Tue, Dec 1, 2020 at 2:25 PM Jason Wang <jasow...@redhat.com> > > > > wrote: > > > > > > > > > > > > > > > > > > > > > On 2020/11/30 下午3:07, Yongji Xie wrote: > > > > > > > >>> Thanks for adding me, Jason! > > > > > > > >>> > > > > > > > >>> Now I'm working on a v2 patchset for VDUSE (vDPA Device in > > > > > > > >>> Userspace) [1]. This tool is very useful for the vduse device. > > > > > > > >>> So I'm considering integrating this into my v2 patchset. > > > > > > > >>> But there is one problem： > > > > > > > >>> > > > > > > > >>> In this tool, vdpa device config action and enable action > > > > > > > >>> are combined into one netlink msg: VDPA_CMD_DEV_NEW. But > > > > > > > >>> in > > > > vduse > > > > > > > >>> case, it needs to be splitted because a chardev should be > > > > > > > >>> created and opened by a userspace process before we enable > > > > > > > >>> the vdpa device (call vdpa_register_device()). > > > > > > > >>> > > > > > > > >>> So I'd like to know whether it's possible (or have some > > > > > > > >>> plans) to add two new netlink msgs something like: > > > > > > > >>> VDPA_CMD_DEV_ENABLE > > > > > > and > > > > > > > >>> VDPA_CMD_DEV_DISABLE to make the config path more flexible. > > > > > > > >>> > > > > > > > >> Actually, we've discussed such intermediate step in some > > > > > > > >> early discussion. It looks to me VDUSE could be one of the > > > > > > > >> users of > > this. > > > > > > > >> > > > > > > > >> Or I wonder whether we can switch to use anonymous > > > > > > > >> inode(fd) for VDUSE then fetching it via an VDUSE_GET_DEVICE_FD > > ioctl? > > > > > > > >> > > > > > > > > Yes, we can. Actually the current implementation in VDUSE is > > > > > > > > like this. But seems like this is still a intermediate step. > > > > > > > > The fd should be binded to a name or something else which > > > > > > > > need to be configured before. > > > > > > > > > > > > > > > > > > > > > The name could be specified via the netlink. It looks to me > > > > > > > the real issue is that until the device is connected with a > > > > > > > userspace, it can't be used. So we also need to fail the > > > > > > > enabling if it doesn't > > > > opened. > > > > > > > > > > > > > > > > > > > Yes, that's true. So you mean we can firstly try to fetch the fd > > > > > > binded to a name/vduse_id via an VDUSE_GET_DEVICE_FD, then use > > > > > > the name/vduse_id as a attribute to create vdpa device? It looks > > > > > > fine to > > me. > > > > > > > > > > I probably do not well understand. I tried reading patch [1] and > > > > > few things > > > > do not look correct as below. > > > > > Creating the vdpa device on the bus device and destroying the > > > > > device from > > > > the workqueue seems unnecessary and racy. > > > > > > > > > > It seems vduse driver needs > > > > > This is something should be done as part of the vdpa dev add > > > > > command, > > > > instead of connecting two sides separately and ensuring race free > > > > access to it. > > > > > > > > > > So VDUSE_DEV_START and VDUSE_DEV_STOP should possibly be avoided. > > > > > > > > > > > > > Yes, we can avoid these two ioctls with the help of the management tool. > > > > > > > > > $ vdpa dev add parentdev vduse_mgmtdev type net name foo2 > > > > > > > > > > When above command is executed it creates necessary vdpa device > > > > > foo2 > > > > on the bus. > > > > > When user binds foo2 device with the vduse driver, in the probe(), > > > > > it > > > > creates respective char device to access it from user space. > > > > > > > I see. So vduse cannot work with any existing vdpa devices like ifc, mlx5 > > > or > > netdevsim. > > > It has its own implementation similar to fuse with its own backend of > > > choice. > > > More below. > > > > > > > But vduse driver is not a vdpa bus driver. It works like vdpasim > > > > driver, but offloads the data plane and control plane to a user space > > > > process. > > > > > > In that case to draw parallel lines, > > > > > > 1. netdevsim: > > > (a) create resources in kernel sw > > > (b) datapath simulates in kernel > > > > > > 2. ifc + mlx5 vdpa dev: > > > (a) creates resource in hw > > > (b) data path is in hw > > > > > > 3. vduse: > > > (a) creates resources in userspace sw > > > (b) data path is in user space. > > > hence creates data path resources for user space. > > > So char device is created, removed as result of vdpa device creation. > > > > > > For example, > > > $ vdpa dev add parentdev vduse_mgmtdev type net name foo2 > > > > > > Above command will create char device for user space. > > > > > > Similar command for ifc/mlx5 would have created similar channel for rest > > > of > > the config commands in hw. > > > vduse channel = char device, eventfd etc. > > > ifc/mlx5 hw channel = bar, irq, command interface etc Netdev sim > > > channel = sw direct calls > > > > > > Does it make sense? > > > > In my understanding, to make vdpa work, we need a backend (datapath > > resources) and a frontend (a vdpa device attached to a vdpa bus). In the > > above > > example, it looks like we use the command "vdpa dev add ..." > > to create a backend, so do we need another command to create a frontend? > > > For block device there is certainly some backend to process the IOs. > Sometimes backend to be setup first, before its front end is exposed.
Yes, the backend need to be setup firstly, this is vendor device specific, not vdpa specific. > "vdpa dev add" is the front end command who connects to the backend > (implicitly) for network device. > > vhost->vdpa_block_device->backend_io_processor (usr,hw,kernel). > > And it needs a way to connect to backend when explicitly specified during > creation time. > Something like, > $ vdpa dev add parentdev vdpa_vduse type block name foo3 handle <uuid> > In above example some vendor device specific unique handle is passed based on > backend setup in hardware/user space. > Yes, we can work like this. After we setup a backend through an anonymous inode(fd) from /dev/vduse, we can get a unique handle. Then use it to create a frontend which will connect to the specific backend. > In below 3 examples, vdpa block simulator is connecting to backend block or > file. > > $ vdpa dev add parentdev vdpa_blocksim type block name foo4 blockdev /dev/zero > > $ vdpa dev add parentdev vdpa_blocksim type block name foo5 blockdev > /dev/sda2 size=100M offset=10M > > $ vdpa dev add parentdev vdpa_block filebackend_sim type block name foo6 file > /root/file_backend.txt > > Or may be backend connects to the created vdpa device is bound to the driver. > Can vduse attach to the created vdpa block device through the char device and > establish the channel to receive IOs, and to setup the block config space? > How to create the vdpa block device? If we use the command "vdpa dev add..", the command will hang there until a vduse process attaches to the vdpa block device. Thanks, Yongji
