On 2020/8/18 下午5:32, Parav Pandit wrote:
Hi Jason,

From: Jason Wang <jasow...@redhat.com>
Sent: Tuesday, August 18, 2020 2:32 PM


On 2020/8/18 下午4:55, Daniel P. Berrangé wrote:
On Tue, Aug 18, 2020 at 11:24:30AM +0800, Jason Wang wrote:
On 2020/8/14 下午1:16, Yan Zhao wrote:
On Thu, Aug 13, 2020 at 12:24:50PM +0800, Jason Wang wrote:
On 2020/8/10 下午3:46, Yan Zhao wrote:
driver is it handled by?
It looks that the devlink is for network device specific, and in
devlink.h, it says
include/uapi/linux/devlink.h - Network physical device Netlink
interface,
Actually not, I think there used to have some discussion last year and the
conclusion is to remove this comment.

[...]

Yes, but it could be hard. E.g vDPA will chose to use devlink (there's a long 
debate on sysfs vs devlink). So if we go with sysfs, at least two APIs needs to 
be supported ...
We had internal discussion and proposal on this topic.
I wanted Eli Cohen to be back from vacation on Wed 8/19, but since this is 
active discussion right now, I will share the thoughts anyway.

Here are the initial round of thoughts and proposal.

User requirements:
---------------------------
1. User might want to create one or more vdpa devices per PCI PF/VF/SF.
2. User might want to create one or more vdpa devices of type net/blk or other 
type.
3. User needs to look and dump at the health of the queues for debug purpose.
4. During vdpa net device creation time, user may have to provide a MAC address 
and/or VLAN.
5. User should be able to set/query some of the attributes for 
debug/compatibility check
6. When user wants to create vdpa device, it needs to know which device 
supports creation.
7. User should be able to see the queue statistics of doorbells, wqes etc 
regardless of class type


Note that wqes is probably not something common in all of the vendors.



To address above requirements, there is a need of vendor agnostic tool, so that 
user can create/config/delete vdpa device(s) regardless of the vendor.

Hence,
We should have a tool that lets user do it.

Examples:
-------------
(a) List parent devices which supports creating vdpa devices.
It also shows which class types supported by this parent device.
In below command two parent devices support vdpa device creation.
First is PCI VF whose bdf is 03.00:5.
Second is PCI SF whose name is mlx5_sf.1

$ vdpa list pd


What did "pd" mean?


pci/0000:03.00:5
   class_supports
     net vdpa
virtbus/mlx5_sf.1


So creating mlx5_sf.1 is the charge of devlink?


   class_supports
     net

(b) Now add a vdpa device and show the device.
$ vdpa dev add pci/0000:03.00:5 type net


So if you want to create devices types other than vdpa on pci/0000:03.00:5 it needs some synchronization with devlink?


$ vdpa dev show
vdpa0@pci/0000:03.00:5 type net state inactive maxqueues 8 curqueues 4

(c) vdpa dev show features vdpa0
iommu platform
version 1

(d) dump vdpa statistics
$ vdpa dev stats show vdpa0
kickdoorbells 10
wqes 100

(e) Now delete a vdpa device previously created.
$ vdpa dev del vdpa0

Design overview:
-----------------------
1. Above example tool runs over netlink socket interface.
2. This enables users to return meaningful error strings in addition to code so 
that user can be more informed.
Often this is missing in ioctl()/configfs/sysfs interfaces.
3. This tool over netlink enables syscaller tests to be more usable like other 
subsystems to keep kernel robust
4. This provides vendor agnostic view of all vdpa capable parent and vdpa 
devices.

5. Each driver which supports vdpa device creation, registers the parent device 
along with supported classes.

FAQs:
--------
1. Why not using devlink?
Ans: Because as vdpa echo system grows, devlink will fall short of extending 
vdpa specific params, attributes, stats.


This should be fine but it's still not clear to me the difference between a vdpa netlink and a vdpa object in devlink.

Thanks



2. Why not use sysfs?
Ans:
(a) Because running syscaller infrastructure can run well over netlink sockets 
like it runs for several subsystem.
(b) it lacks the ability to return error messages. Doing via kernel log is just 
doesn't work.
(c) Why not using some ioctl()? It will reinvent the wheel of netlink that has 
TLV formats for several attributes.

3. Why not configs?
It follows same limitation as that of sysfs.

Low level design and driver APIS:
--------------------------------------------
Will post once we discuss this further.

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