Re: [dpdk-dev] [PATCH v2] common/mlx5: add provider query port support to glue library

[Slava Ovsiienko <viacheslavo@nvidia.com>]

Hi, David

Thank you for the review and comments.
What do you think about the commit message like this?

common/mlx5: fix rdma-core v35 query port API support

The rdma-core mlx5 provider introduced the port attributes query
API since version v35.0 - the mlx5dv_query_port routine. In order
to support this change in the rdma-core the conditional compilation
flag HAVE_MLX5DV_DR_DEVX_PORT_V35 is introduced by the this patch.

In the OFED rdma-core version the new compatible mlx5dv_query_port
routine was introduced as well, replacing the existing proprietary
mlx5dv_query_devx_port routine. The proprietary routine was
controlled in PMD code with HAVE_MLX5DV_DR_DEVX_PORT conditional
flag.

Currently, the OFED rdma-core library contains both versions of
port query API. And this version is a transitional one, there are
the plans to remove the proprietary mlx5dv_query_devx_port routine
and the HAVE_MLX5DV_DR_DEVX_PORT flag in PMD will not work anymore.

We had one more dependency on this flag in the code (for the
mlx5dv_dr_action_create_dest_ib_port routine) and the patch
fixes mentioned dependency also, by introducing the new
dedicated conditional flag - HAVE_MLX5DV_DR_CREATE_DEST_IB_PORT.

The introduced port query API is related to getting kernel
metadata indices assigned to the vports of E-switch. Without
engaging the API the PMD makes the assumptions about the indices,
those might be incorrect for some configurations (for example -
LAG ones) and the E-switch feature might not operate correctly.

This patch is highly desirable to be provided in DPDK LTS releases
due to it covers the major compatibility issue.

(I will add cc: and fixes tag while sending the update)

With best regards,
Slava


> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Wednesday, June 23, 2021 16:52
> To: Slava Ovsiienko <viacheslavo@nvidia.com>
> Cc: dev <dev@dpdk.org>; Raslan Darawsheh <rasland@nvidia.com>; Matan
> Azrad <matan@nvidia.com>; NBU-Contact-Thomas Monjalon
> <thomas@monjalon.net>; dpdk stable <stable@dpdk.org>
> Subject: Re: [dpdk-dev] [PATCH v2] common/mlx5: add provider query port
> support to glue library
> 
> On Wed, Jun 23, 2021 at 1:27 PM Slava Ovsiienko <viacheslavo@nvidia.com>
> wrote:
> > > > This patch is highly desirable to be provided in DPDK LTS releases
> > > > due to it covers the major compatibility issue.
> > >
> > > This patch is a fix, yet nothing tells this story in the title.
> >
> > This patch is not a fix. Actually it covers the compatibility issue, not a bug.
> 
> I still think it counts as a fix in the sense that the mlx5 driver behavior
> changes to an undesired state if rdma-core gets updated.
> 
> It's not about preferring "fix" in the title.
> It is more accurate/descriptive to me.
> If you feel strongly against "fix", I won't insist.
> 
> Yet "add provider quer port support to glue library" is just black magic to
> most of us.
> 
> 
> > The Upstream rdma-core was evolved, its community adopted a slightly
> > different API version than was presented in the vendor version.
> > Our PMD should conform both versions and we provided this patch for
> DPDK.
> 
> Let's try differently.
> Place yourself as someone who does not know a thing about the mlx5 driver
> and rdma-core.
> How does such a person understand the impact of this patch?
> 
> I would state in the title that the mlx5 driver can now handle correctly rdma-
> core 35.
> Additionally, it could indicate which feature X is now behaving as intended.
> But if feature X is something internal to the mlx5 driver, it is worth skipping.
> 
> 
> 
> --
> David Marchand