Re: [PATCH net-next 0/2] devlink: Add port function attribute to enable/disable roce

On Tue, 2021-02-02 at 18:14 -0800, Jakub Kicinski wrote:

On Mon, 1 Feb 2021 19:51:50 +0200 Yishai Hadas wrote:

quoted

Currently mlx5 PCI VF and SF are enabled by default for RoCE
functionality.

Currently a user does not have the ability to disable RoCE for a
PCI
VF/SF device before such device is enumerated by the driver.

User is also incapable to do such setting from smartnic scenario
for a
VF from the smartnic.

Current 'enable_roce' device knob is limited to do setting only at
driverinit time. By this time device is already created and
firmware has
already allocated necessary system memory for supporting RoCE.

When a RoCE is disabled for the PCI VF/SF device, it saves 1 Mbyte
of
system memory per function. Such saving is helpful when running on
low
memory embedded platform with many VFs or SFs.

Therefore, it is desired to empower user to disable RoCE
functionality
before a PCI SF/VF device is enumerated.

You say that the user on the VF/SF side wants to save memory, yet
the control knob is on the eswitch instance side, correct?

yes, user in this case is the admin, who controls the provisioned
network function SF/VFs.. by turning off this knob it allows to create
more of that resource in case the user/admin is limited by memory.

quoted

This is achieved by extending existing 'port function' object to
control
capabilities of a function. This enables users to control
capability of
the device before enumeration.

Examples when user prefers to disable RoCE for a VF when using
switchdev
mode:

$ devlink port show pci/0000:06:00.0/1
pci/0000:06:00.0/1: type eth netdev pf0vf0 flavour pcivf controller
0
pfnum 0 vfnum 0 external false splittable false
  function:
    hw_addr 00:00:00:00:00:00 roce on

$ devlink port function set pci/0000:06:00.0/1 roce off
  
$ devlink port show pci/0000:06:00.0/1
pci/0000:06:00.0/1: type eth netdev pf0vf0 flavour pcivf controller
0
pfnum 0 vfnum 0 external false splittable false
  function:
    hw_addr 00:00:00:00:00:00 roce off

FAQs:
-----
1. What does roce on/off do?
Ans: It disables RoCE capability of the function before its
enumerated,
so when driver reads the capability from the device firmware, it is
disabled.
At this point RDMA stack will not be able to create UD, QP1, RC,
XRC
type of QPs. When RoCE is disabled, the GID table of all ports of
the
device is disabled in the device and software stack.

2. How is the roce 'port function' option different from existing
devlink param?
Ans: RoCE attribute at the port function level disables the RoCE
capability at the specific function level; while enable_roce only
does
at the software level.

3. Why is this option for disabling only RoCE and not the whole
RDMA
device?
Ans: Because user still wants to use the RDMA device for non RoCE
commands in more memory efficient way.

What are those "non-RoCE commands" that user may want to use "in a
more
efficient way"?

RAW eth QP, i think you already know this one, it is a very thin layer
that doesn't require the whole rdma stack.