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From: Yongji Xie <xieyongji@bytedance.com>
To: Jason Wang <jasowang@redhat.com>
Cc: Parav Pandit <parav@nvidia.com>,
	"virtualization@lists.linux-foundation.org" 
	<virtualization@lists.linux-foundation.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Eli Cohen <elic@nvidia.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [External] Re: [PATCH 0/7] Introduce vdpa management tool
Date: Wed, 2 Dec 2020 17:27:13 +0800
Message-ID: <CACycT3uifi3ckbixEX1sCsU0jVRb74ONrbKS2SoMVHmq+pgLgg@mail.gmail.com> (raw)
In-Reply-To: <3d91bf80-1a35-9f79-dbca-596358acc0a7@redhat.com>

On Wed, Dec 2, 2020 at 1:51 PM Jason Wang <jasowang@redhat.com> wrote:
>
>
> On 2020/12/2 下午12:53, Parav Pandit wrote:
> >
> >> From: Yongji Xie <xieyongji@bytedance.com>
> >> Sent: Wednesday, December 2, 2020 9:00 AM
> >>
> >> On Tue, Dec 1, 2020 at 11:59 PM Parav Pandit <parav@nvidia.com> wrote:
> >>>
> >>>
> >>>> From: Yongji Xie <xieyongji@bytedance.com>
> >>>> Sent: Tuesday, December 1, 2020 7:49 PM
> >>>>
> >>>> On Tue, Dec 1, 2020 at 7:32 PM Parav Pandit <parav@nvidia.com> wrote:
> >>>>>
> >>>>>
> >>>>>> From: Yongji Xie <xieyongji@bytedance.com>
> >>>>>> Sent: Tuesday, December 1, 2020 3:26 PM
> >>>>>>
> >>>>>> On Tue, Dec 1, 2020 at 2:25 PM Jason Wang <jasowang@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.
> > "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.
> >
> > 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?
>
>
> I think it can work.
>
> Another thing I wonder it that, do we consider more than one VDUSE
> parentdev(or management dev)? This allows us to have separated devices
> implemented via different processes.
>
> If yes, VDUSE ioctl needs to be extended to register/unregister parentdev.
>

Yes, we need to extend the ioctl to support that. Now we only have one
parentdev represented by /dev/vduse.

Thanks,
Yongji

  parent reply index

Thread overview: 79+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-12  6:39 Parav Pandit
2020-11-12  6:39 ` [PATCH 1/7] vdpa: Add missing comment for virtqueue count Parav Pandit
2020-11-12  6:40 ` [PATCH 2/7] vdpa: Use simpler version of ida allocation Parav Pandit
2020-11-12  6:40 ` [PATCH 3/7] vdpa: Extend routine to accept vdpa device name Parav Pandit
2020-11-12  6:40 ` [PATCH 4/7] vdpa: Define vdpa parent device, ops and a netlink interface Parav Pandit
2020-11-12  6:40 ` [PATCH 5/7] vdpa: Enable a user to add and delete a vdpa device Parav Pandit
2020-11-12  6:40 ` [PATCH 6/7] vdpa: Enable user to query vdpa device info Parav Pandit
2020-11-12  6:40 ` [PATCH 7/7] vdpa/vdpa_sim: Enable user to create vdpasim net devices Parav Pandit
2020-11-16  9:41 ` [PATCH 0/7] Introduce vdpa management tool Stefan Hajnoczi
2020-11-17 19:41   ` Parav Pandit
2020-11-16 22:23 ` Jakub Kicinski
2020-11-17 19:51   ` Parav Pandit
2020-12-16  9:13     ` Michael S. Tsirkin
     [not found]       ` <20201216080610.08541f44@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
2020-12-16 16:54         ` Parav Pandit
2020-12-16 19:57           ` Michael S. Tsirkin
2020-12-17 12:13             ` Parav Pandit
2020-11-27  3:53 ` Jason Wang
     [not found]   ` <CACycT3sYScObb9nN3g7L3cesjE7sCZWxZ5_5R1usGU9ePZEeqA@mail.gmail.com>
2020-11-30  3:36     ` [External] " Jason Wang
2020-11-30  7:07       ` Yongji Xie
2020-12-01  6:25         ` Jason Wang
2020-12-01  9:55           ` Yongji Xie
2020-12-01 11:32             ` Parav Pandit
2020-12-01 14:18               ` Yongji Xie
2020-12-01 15:58                 ` Parav Pandit
2020-12-02  3:29                   ` Yongji Xie
2020-12-02  4:53                     ` Parav Pandit
2020-12-02  5:51                       ` Jason Wang
2020-12-02  6:24                         ` Parav Pandit
2020-12-02  7:55                           ` Jason Wang
2020-12-02  9:27                         ` Yongji Xie [this message]
2020-12-02  9:21                       ` Yongji Xie
2020-12-02 11:13                         ` Parav Pandit
2020-12-02 13:18                           ` Yongji Xie
2020-12-02  5:48             ` Jason Wang
2020-12-08 22:47   ` David Ahern
2021-01-19  4:21     ` Parav Pandit
2020-12-16  9:16 ` Michael S. Tsirkin
2021-01-04  3:31 ` [PATCH linux-next v2 " Parav Pandit
2021-01-04  3:31   ` [PATCH linux-next v2 1/7] vdpa_sim_net: Make mac address array static Parav Pandit
2021-01-04  7:00     ` Jason Wang
2021-01-04  3:31   ` [PATCH linux-next v2 2/7] vdpa_sim_net: Add module param to disable default vdpa net device Parav Pandit
2021-01-04  3:31   ` [PATCH linux-next v2 3/7] vdpa: Extend routine to accept vdpa device name Parav Pandit
2021-01-04  3:31   ` [PATCH linux-next v2 4/7] vdpa: Define vdpa mgmt device, ops and a netlink interface Parav Pandit
2021-01-04  7:03     ` Jason Wang
2021-01-04  7:24       ` Parav Pandit
2021-01-05  4:10         ` Jason Wang
2021-01-05  6:33           ` Parav Pandit
2021-01-05  8:36             ` Jason Wang
2021-01-04  3:31   ` [PATCH linux-next v2 5/7] vdpa: Enable a user to add and delete a vdpa device Parav Pandit
2021-01-04  3:31   ` [PATCH linux-next v2 6/7] vdpa: Enable user to query vdpa device info Parav Pandit
2021-01-04  3:31   ` [PATCH linux-next v2 7/7] vdpa_sim_net: Add support for user supported devices Parav Pandit
2021-01-04  7:05     ` Jason Wang
2021-01-04  7:21       ` Parav Pandit
2021-01-05  4:06         ` Jason Wang
2021-01-05  6:22           ` Parav Pandit
2021-01-05 10:31 ` [PATCH linux-next v3 0/6] Introduce vdpa management tool Parav Pandit
2021-01-05 10:31   ` [PATCH linux-next v3 1/6] vdpa_sim_net: Make mac address array static Parav Pandit
2021-01-07 13:45     ` Stefano Garzarella
2021-01-05 10:31   ` [PATCH linux-next v3 2/6] vdpa: Extend routine to accept vdpa device name Parav Pandit
2021-01-05 10:32   ` [PATCH linux-next v3 3/6] vdpa: Define vdpa mgmt device, ops and a netlink interface Parav Pandit
2021-01-05 10:32   ` [PATCH linux-next v3 4/6] vdpa: Enable a user to add and delete a vdpa device Parav Pandit
2021-01-05 10:32   ` [PATCH linux-next v3 5/6] vdpa: Enable user to query vdpa device info Parav Pandit
2021-01-05 10:32   ` [PATCH linux-next v3 6/6] vdpa_sim_net: Add support for user supported devices Parav Pandit
2021-01-05 11:48     ` Michael S. Tsirkin
2021-01-05 12:02       ` Parav Pandit
2021-01-05 12:14         ` Michael S. Tsirkin
2021-01-05 12:30           ` Parav Pandit
2021-01-05 13:23             ` Michael S. Tsirkin
2021-01-07  3:48               ` Parav Pandit
2021-01-12  4:14                 ` Parav Pandit
2021-01-14  4:17                 ` Jason Wang
2021-01-14  7:58                   ` Parav Pandit
2021-01-15  5:38                     ` Jason Wang
2021-01-15  6:27                       ` Parav Pandit
2021-01-19 11:09                         ` Jason Wang
2021-01-20  3:21                           ` Parav Pandit
2021-01-20  3:46                             ` Parav Pandit
2021-01-18 18:03                       ` Parav Pandit
2021-01-20  7:53                         ` Michael S. Tsirkin

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