linux-kernel - Re: [PATCH net-next v8 07/13] net: pse-pd: Add support for budget evaluation strategies

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Message-ID: <aAD2RN_PV79rpf1Q@pengutronix.de>
Date: Thu, 17 Apr 2025 14:38:28 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Kory Maincent <kory.maincent@...tlin.com>
Cc: Andrew Lunn <andrew@...n.ch>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Donald Hunter <donald.hunter@...il.com>,
	Rob Herring <robh@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>,
	Simon Horman <horms@...nel.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	netdev@...r.kernel.org, linux-doc@...r.kernel.org,
	Kyle Swenson <kyle.swenson@....tech>,
	Dent Project <dentproject@...uxfoundation.org>,
	kernel@...gutronix.de,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v8 07/13] net: pse-pd: Add support for budget
 evaluation strategies

On Wed, Apr 16, 2025 at 03:44:22PM +0200, Kory Maincent wrote:
> From: Kory Maincent (Dent Project) <kory.maincent@...tlin.com>
> 
> This patch introduces the ability to configure the PSE PI budget evaluation
> strategies. Budget evaluation strategies is utilized by PSE controllers to
> determine which ports to turn off first in scenarios such as power budget
> exceedance.
> 
> The pis_prio_max value is used to define the maximum priority level
> supported by the controller. Both the current priority and the maximum
> priority are exposed to the user through the pse_ethtool_get_status call.
> 
> This patch add support for two mode of budget evaluation strategies.
> 1. Static Method:
> 
>    This method involves distributing power based on PD classification.
>    It’s straightforward and stable, the PSE core keeping track of the
>    budget and subtracting the power requested by each PD’s class.
> 
>    Advantages: Every PD gets its promised power at any time, which
>    guarantees reliability.
> 
>    Disadvantages: PD classification steps are large, meaning devices
>    request much more power than they actually need. As a result, the power
>    supply may only operate at, say, 50% capacity, which is inefficient and
>    wastes money.
> 
>    Priority max value is matching the number of PSE PIs within the PSE.
> 
> 2. Dynamic Method:
> 
>    To address the inefficiencies of the static method, vendors like
>    Microchip have introduced dynamic power budgeting, as seen in the
>    PD692x0 firmware. This method monitors the current consumption per port
>    and subtracts it from the available power budget. When the budget is
>    exceeded, lower-priority ports are shut down.
> 
>    Advantages: This method optimizes resource utilization, saving costs.
> 
>    Disadvantages: Low-priority devices may experience instability.
> 
>    Priority max value is set by the PSE controller driver.
> 
> For now, budget evaluation methods are not configurable and cannot be
> mixed. They are hardcoded in the PSE driver itself, as no current PSE
> controller supports both methods.
> 
> Signed-off-by: Kory Maincent (Dent Project) <kory.maincent@...tlin.com>

Reviewed-by: Oleksij Rempel <o.rempel@...gutronix.de>

Thank you!

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