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From: Yongji Xie <xieyongji@bytedance.com>
To: Parav Pandit <parav@nvidia.com>
Cc: Jason Wang <jasowang@redhat.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 17:21:54 +0800
Message-ID: <CACycT3uV8e61kVF6Q8zE5VVK_Okp03e=WNRcUffdkFeeFpfKDQ@mail.gmail.com> (raw)
In-Reply-To: <BY5PR12MB4322446CDB07B3CC5603F7D1DCF30@BY5PR12MB4322.namprd12.prod.outlook.com>

On Wed, Dec 2, 2020 at 12:53 PM Parav Pandit <parav@nvidia.com> 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.

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

  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
2020-12-02  9:21                       ` Yongji Xie [this message]
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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