netdev - Re: [Power Efficiency Proposal] Low Power on Media Disconnect

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Message-ID: <1281938880.2942.68.camel@edumazet-laptop>
Date:	Mon, 16 Aug 2010 08:08:00 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	LionSky <loverunning2@...il.com>
Cc:	netdev@...r.kernel.org, jie.yang@...eros.com
Subject: Re: [Power Efficiency Proposal] Low Power on Media Disconnect

Le lundi 16 août 2010 à 13:35 +0800, LionSky a écrit :
> It is a very typical scenario that users of laptop/Netbook experience
> Internet over wireless instead of ethernet.
> An obvious hint about that is user unplug-in the ethernet cable which
> implies that he does not want to use the ethernet. So for power
> efficiency, it is best to place ethernet adapter into a low power
> state, such as C3hot, when ethernet cable is disconnected.
> Battery life is very important for Laptop/Netbook. Currently, the
> power consumption of active idle on a typical Netbook is about 5-6
> Watt. If you placed the etherent adapter in C3hot state, about
> 0.5~1.0Watt power is saved which depneds on your H/W. This can prolong
> battery life about 10%~20% which is a quite big power saving.
> Now, Linux kernel supports runtime power management. It is not a hard
> work to enable this feature on each ethernet adapter driver.
> 
> Here I attached a simple and prototype implementation which is
> verified on a Netbook (ASUS E1005PE with Atheros AR8132 PCI-E Fast
> Ethernet Controller).
> 1. When ethernet cable is disconnected, driver places ethernet adapter
> into D3hot low power state. Just as CPU go to deep C-State.
> 2. When ethernet cable is connected again, driver places ethernet back
> in D0 power state.
> 
> To further improve the power behavior of Linux on laptop/Netbook, a
> proposal is that all ethernet drivers must support Low Power on Media

 ... should support ...

> Disconnect.
> 
> Is it right? Welcome any comments.
> 

I cannot say if this patch is right on the power side.
(Would it be better to handle the ethernet device power switch from a
user policy daemon, instead of forcing the policy from the driver ?)
I dont know the implications of Low Power on Media disconnect.
At least, let ethtool be able to switch on or off this automatic
behavior...

But your patch introduces a shared (static actually) variable, atl1c_d3.
Are you sure a single state is enough to handle several ethernet ports ?



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