Re: [Qemu-devel] [PATCH v3 23/23] docs: Update pvrdma device documentation

[Yuval Shaia <yuval.shaia@oracle.com>]

On Sat, Nov 17, 2018 at 02:34:18PM +0200, Marcel Apfelbaum wrote:
> 
> 
> On 11/13/18 9:13 AM, Yuval Shaia wrote:
> > Interface with the device is changed with the addition of support for
> > MAD packets.
> > Adjust documentation accordingly.
> > 
> > While there fix a minor mistake which may lead to think that there is a
> > relation between using RXE on host and the compatibility with bare-metal
> > peers.
> > 
> > Signed-off-by: Yuval Shaia <yuval.shaia@oracle.com>
> > ---
> >   docs/pvrdma.txt | 103 +++++++++++++++++++++++++++++++++++++++---------
> >   1 file changed, 84 insertions(+), 19 deletions(-)
> > 
> > diff --git a/docs/pvrdma.txt b/docs/pvrdma.txt
> > index 5599318159..9e8d1674b7 100644
> > --- a/docs/pvrdma.txt
> > +++ b/docs/pvrdma.txt
> > @@ -9,8 +9,9 @@ It works with its Linux Kernel driver AS IS, no need for any special guest
> >   modifications.
> >   While it complies with the VMware device, it can also communicate with bare
> > -metal RDMA-enabled machines and does not require an RDMA HCA in the host, it
> > -can work with Soft-RoCE (rxe).
> > +metal RDMA-enabled machines as peers.
> > +
> > +It does not require an RDMA HCA in the host, it can work with Soft-RoCE (rxe).
> >   It does not require the whole guest RAM to be pinned allowing memory
> >   over-commit and, even if not implemented yet, migration support will be
> > @@ -78,29 +79,93 @@ the required RDMA libraries.
> >   3. Usage
> >   ========
> > +
> > +
> > +3.1 VM Memory settings
> > +======================
> >   Currently the device is working only with memory backed RAM
> >   and it must be mark as "shared":
> >      -m 1G \
> >      -object memory-backend-ram,id=mb1,size=1G,share \
> >      -numa node,memdev=mb1 \
> > -The pvrdma device is composed of two functions:
> > - - Function 0 is a vmxnet Ethernet Device which is redundant in Guest
> > -   but is required to pass the ibdevice GID using its MAC.
> > -   Examples:
> > -     For an rxe backend using eth0 interface it will use its mac:
> > -       -device vmxnet3,addr=<slot>.0,multifunction=on,mac=<eth0 MAC>
> > -     For an SRIOV VF, we take the Ethernet Interface exposed by it:
> > -       -device vmxnet3,multifunction=on,mac=<RoCE eth MAC>
> > - - Function 1 is the actual device:
> > -       -device pvrdma,addr=<slot>.1,backend-dev=<ibdevice>,backend-gid-idx=<gid>,backend-port=<port>
> > -   where the ibdevice can be rxe or RDMA VF (e.g. mlx5_4)
> > - Note: Pay special attention that the GID at backend-gid-idx matches vmxnet's MAC.
> > - The rules of conversion are part of the RoCE spec, but since manual conversion
> > - is not required, spotting problems is not hard:
> > -    Example: GID: fe80:0000:0000:0000:7efe:90ff:fecb:743a
> > -             MAC: 7c:fe:90:cb:74:3a
> > -    Note the difference between the first byte of the MAC and the GID.
> > +
> > +3.2 MAD Multiplexer
> > +===================
> > +MAD Multiplexer is a service that exposes MAD-like interface for VMs in
> > +order to overcome the limitation where only single entity can register with
> > +MAD layer to send and receive RDMA-CM MAD packets.
> > +
> > +To build rdmacm-mux run
> > +# make rdmacm-mux
> > +
> > +The program accepts 3 command line arguments and exposes a UNIX socket to
> > +be used to relay control and data messages to and from the service.
> > +-s unix-socket-path   Path to unix socket to listen on
> > +                      (default /var/run/rdmacm-mux)
> > +-d rdma-device-name   Name of RDMA device to register with
> > +                      (default rxe0)
> > +-p rdma-device-port   Port number of RDMA device to register with
> > +                      (default 1)
> > +The final UNIX socket file name is a concatenation of the 3 arguments so
> > +for example for device name mlx5_0 and port 2 the file
> > +/var/run/rdmacm-mux-mlx5_0-2 will be created.
> > +
> > +Please refer to contrib/rdmacm-mux for more details.
> > +
> > +
> > +3.3 PCI devices settings
> > +========================
> > +RoCE device exposes two functions - Ethernet and RDMA.
> > +To support it, pvrdma device is composed of two PCI functions, an Ethernet
> > +device of type vmxnet3 on PCI slot 0 and a pvrdma device on PCI slot 1. The
> > +Ethernet function can be used for other Ethernet purposes such as IP.
> > +
> > +
> > +3.4 Device parameters
> > +=====================
> > +- netdev: Specifies the Ethernet device on host. For Soft-RoCE (rxe) this
> > +  would be the Ethernet device used to create it. For any other physical
> > +  RoCE device this would be the netdev name of the device.
> 
> I didn't understand, can you please elaborate? We need the ibdev,
> this is clear, but what is the "ethernet device on host", how do
> we get it and how it is used?

netdev is used to maintain port's GID table.

Adding GID entry is by assigning new IPv6 address to the corresponding
Ethernet function, opposite is the same, i.e. removing an IPv6 address from
the Ethernet function will delete the corresponding GID from the GID table.

I wish there would be a way to extract netdev from a given ibdev (by means
of an API) but since there isn't - we must have it as a parameter.

> 
> Thanks,
> Marcel
> 
> > +- ibdev: The IB device name on host for example rxe0, mlx5_0 etc.
> > +- mad-chardev: The name of the MAD multiplexer char device.
> > +- ibport: In case of multi-port device (such as Mellanox's HCA) this
> > +  specify the port to use. If not set 1 will be used.
> > +- dev-caps-max-mr-size: The maximum size of MR.
> > +- dev-caps-max-qp: Maximum number of QPs.
> > +- dev-caps-max-sge: Maximum number of SGE elements in WR.
> > +- dev-caps-max-cq: Maximum number of CQs.
> > +- dev-caps-max-mr: Maximum number of MRs.
> > +- dev-caps-max-pd: Maximum number of PDs.
> > +- dev-caps-max-ah: Maximum number of AHs.
> > +
> > +Notes:
> > +- The first 3 parameters are mandatory settings, the rest have their
> > +  defaults.
> > +- The last 8 parameters (the ones that prefixed by dev-caps) defines the top
> > +  limits but the final values are adjusted by the backend device limitations.
> > +
> > +3.5 Example
> > +===========
> > +Define bridge device with vmxnet3 network backend:
> > +<interface type='bridge'>
> > +  <mac address='56:b4:44:e9:62:dc'/>
> > +  <source bridge='bridge1'/>
> > +  <model type='vmxnet3'/>
> > +  <address type='pci' domain='0x0000' bus='0x00' slot='0x10' function='0x0' multifunction='on'/>
> > +</interface>
> > +
> > +Define pvrdma device:
> > +<qemu:commandline>
> > +  <qemu:arg value='-object'/>
> > +  <qemu:arg value='memory-backend-ram,id=mb1,size=1G,share'/>
> > +  <qemu:arg value='-numa'/>
> > +  <qemu:arg value='node,memdev=mb1'/>
> > +  <qemu:arg value='-chardev'/>
> > +  <qemu:arg value='socket,path=/var/run/rdmacm-mux-rxe0-1,id=mads'/>
> > +  <qemu:arg value='-device'/>
> > +  <qemu:arg value='pvrdma,addr=10.1,ibdev=rxe0,netdev=bridge0,mad-chardev=mads'/>
> > +</qemu:commandline>
>