netdev - Re: [RFC PATCH net-next 0/2] devlink: Add port stats

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Date:   Thu, 7 Apr 2022 20:16:38 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Michael Guralnik <michaelgur@...dia.com>
Cc:     <netdev@...r.kernel.org>, <jiri@...dia.com>, <ariela@...dia.com>,
        <maorg@...dia.com>, <saeedm@...dia.com>, <moshe@...dia.com>
Subject: Re: [RFC PATCH net-next 0/2] devlink: Add port stats

On Thu, 7 Apr 2022 11:40:48 +0300 Michael Guralnik wrote:
> This patch set adds port statistics to the devlink port object.
> It allows device drivers to dynamically attach and detach counters from a
> devlink port object.

The challenge in defining APIs for stats is not in how to wrap a free
form string in a netlink message but how do define values that have
clear semantics and are of value to the user.

Start from that, discuss what you have with the customer who requested
the feature. Then think about the API.

I have said this multiple times to multiple people on your team.

> The approach of adding object-attached statistics is already supported for trap
> with traffic statistics and for the dev object with reload statistics.

That's an entirely false comparison.

> For the port object, this will allow the device driver to expose and dynamicly
> control a set of metrics related to the port.
> Currently we add support only for counters, but later API extensions can be made
> to support histograms or configurable counters.
> 
> The statistics are exposed to the user with the port get command.
> 
> Example:
> # devlink -s port show
> pci/0000:00:0b.0/65535: type eth netdev eth1 flavour physical port 0 splittable false
>   stats:
>     counter1 235
>     counter2 18