netdev - Re: [Intel-wired-lan] [PATCH iwl-next v4 4/5] ice: Add tx_scheduling

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Date: Tue, 27 Feb 2024 14:05:45 +0100
From: Przemek Kitszel <przemyslaw.kitszel@...el.com>
To: Jiri Pirko <jiri@...nulli.us>, Jakub Kicinski <kuba@...nel.org>
CC: Mateusz Polchlopek <mateusz.polchlopek@...el.com>,
	<intel-wired-lan@...ts.osuosl.org>, <netdev@...r.kernel.org>,
	<horms@...nel.org>, Lukasz Czapnik <lukasz.czapnik@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v4 4/5] ice: Add
 tx_scheduling_layers devlink param

On 2/27/24 13:17, Jiri Pirko wrote:
> Tue, Feb 27, 2024 at 03:37:00AM CET, kuba@...nel.org wrote:
>> On Sun, 25 Feb 2024 08:18:00 +0100 Jiri Pirko wrote:
>>>> Do you recall any specific param that got rejected from mlx5?
>>>> Y'all were allowed to add the eq sizing params, which I think
>>>> is not going to be mlx5-only for long. Otherwise I only remember
>>>> cases where I'd try to push people to use the resource API, which
>>>> IMO is better for setting limits and delegating resources.
>>>
>>> I don't have anything solid in mind, I would have to look it up. But
>>> there is certainly quite big amount of uncertainties among my
>>> colleagues to jundge is some param would or would not be acceptable to
>>> you. That's why I believe it would save a lot of people time to write
>>> the policy down in details, with examples, etc. Could you please?
>>
>> How about this? (BTW took me half an hour to write, just in case
>> you're wondering)

Thank you!

>>
>> diff --git a/Documentation/networking/devlink/devlink-params.rst b/Documentation/networking/devlink/devlink-params.rst
>> index 4e01dc32bc08..f1eef6d065be 100644
>> --- a/Documentation/networking/devlink/devlink-params.rst
>> +++ b/Documentation/networking/devlink/devlink-params.rst
>> @@ -9,10 +9,12 @@ level device functionality. Since devlink can operate at the device-wide
>> level, it can be used to provide configuration that may affect multiple
>> ports on a single device.
>>
>> -This document describes a number of generic parameters that are supported
>> -across multiple drivers. Each driver is also free to add their own
>> -parameters. Each driver must document the specific parameters they support,
>> -whether generic or not.
>> +There are two categories of devlink parameters - generic parameters
>> +and device-specific quirks. Generic devlink parameters are configuration
>> +knobs which don't fit into any larger API, but are supported across multiple

re Jiri: Generic ones are described here.

>> +drivers. This document describes a number of generic parameters.
>> +Each driver can also add its own parameters, which are documented in driver
>> +specific files.
>>
>> Configuration modes
>> ===================
>> @@ -137,3 +139,32 @@ own name.
>>     * - ``event_eq_size``
>>       - u32
>>       - Control the size of asynchronous control events EQ.
>> +
>> +Adding new params
>> +=================
>> +
>> +Addition of new devlink params is carefully scrutinized upstream.
>> +More complete APIs (in devlink, ethtool, netdev etc.) are always preferred,
>> +devlink params should never be used in their place e.g. to allow easier
>> +delivery via out-of-tree modules, or to save development time.
>> +
>> +devlink parameters must always be thoroughly documented, both from technical
>> +perspective (to allow meaningful upstream review), and from user perspective
>> +(to allow users to make informed decisions).
>> +
>> +The requirements above should make it obvious that any "automatic" /
>> +"pass-through" registration of devlink parameters, based on strings
>> +read from the device, will not be accepted.
>> +
>> +There are two broad categories of devlink params which had been accepted
>> +in the past:
>> +
>> + - device-specific configuration knobs, which cannot be inferred from
>> +   other device configuration. Note that the author is expected to study
>> +   other drivers to make sure that the configuration is in fact unique
>> +   to the implementation.

What if it would not be unique, should they then proceed to add generic
(other word would be "common") param, and make the other driver/s use
it? Without deprecating the old method ofc.

What about knob being vendor specific, but given vendor has multiple,
very similar drivers? (ugh)

>> +
>> + - configuration which must be set at device initialization time.
>> +   Allowing user to enable features at runtime is always preferable
>> +   but in reality most devices allow certain features to be enabled/disabled
>> +   only by changing configuration stored in NVM.
> 
> Looks like most of the generic params does not fit either of these 2
> categories. Did you mean these 2 categories for driver specific?

If you mean the two paragraphs above (both started by "-"), this is for
vendor specific knobs, and reads fine.