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

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Date:	Mon, 16 Aug 2010 13:35:44 +0800
From:	LionSky <loverunning2@...il.com>
To:	netdev@...r.kernel.org
Cc:	jie.yang@...eros.com, weiliang lin <loverunning2@...il.com>
Subject: [Power Efficiency Proposal] Low Power on Media Disconnect

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
Disconnect.

Is it right? Welcome any comments.

Thanks
-Lionsky

View attachment "patch.atl1c.rt.txt" of type "text/plain" (3854 bytes)