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

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Date:	Mon, 16 Aug 2010 15:00:34 +0800
From:	LionSky <loverunning2@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, jie.yang@...eros.com
Subject: Re: [Power Efficiency Proposal] Low Power on Media Disconnect

Thanks Eric,
Yes, you are right. It is better to handle the ethernet device power
switch from a user policy daemon.
This is just a proposal about Low Power on Media Disconnect which
means when media, such as ethernet cable, is disconnected, the related
device should be placed in a low power state, such as D3hot.
Maybe we needs a smart implementation.

Thanks
-Lionsky

2010/8/16 Eric Dumazet <eric.dumazet@...il.com>:
> 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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